Select multiple values and ORDER BY using Kotlin Exposed SQL DSL

Issue

Im trying to make the next query making use of Kotlin SQL Exposed framework.

SELECT interation_id, group_id, max(version)
FROM interaction
GROUP BY group_id;

I have a table of interactions, and each interaction group can have multiple interactions, each one marked with a different version. I want to retrieve the Interaction ID of each group with their latest version

Using exposed my query looks something like:

UserTable
    .slice(UserTable.id, UserTable.version.max())
    .selectAll()
    .groupBy(UserTable.versionGroupID)
    .toList()

yet I get an error of UserTable.id must appear in the GROUP BY clause or be used in an aggregate function. But if i do this my group by will not return a single value for versionGroupId.

Extra input: An example of what i would like to reproduce would be from this table.

Interaction_id	group_id	version
0	1	0
1	2	0
2	2	1
3	2	2
4	1	1
5	1	2
6	2	3

I would like to get has a result Ids: 5 and 6. Those are the last version of each group ID.

Interaction_id	group_id	version
3	1	2
6	2	3

Anyone that have make use of kotlin Exposed SDK(or maybe is a SQL exposed trouble on my side) can give me a hand? Thanks!

Solution

You have to create a subquery to find the maximum version for each group in the InteractionTable and then joined this subquery with the original table to fetch the interaction_id for each group corresponding to the maximum version.

Try this

     val MaxVersionPerGroup = InteractionTable
    .slice(InteractionTable.versionGroupID, InteractionTable.version.max())
    .selectAll()
    .groupBy(InteractionTable.versionGroupID)
    .alias("MaxVersionPerGroup")

val maxVersionColumn = MaxVersionPerGroup[InteractionTable.version.max()]

val query = InteractionTable
    .join(MaxVersionPerGroup, JoinType.INNER, additionalConstraint = { 
        InteractionTable.versionGroupID eq MaxVersionPerGroup[InteractionTable.versionGroupID] and
        InteractionTable.version eq maxVersionColumn
    })
    .slice(InteractionTable.interation_id, InteractionTable.group_id, InteractionTable.version)
    .selectAll()

query.forEach { 
    println("Interaction ID: ${it[InteractionTable.interation_id]}, Group ID: ${it[InteractionTable.group_id]}, Version: ${it[InteractionTable.version]}")
}

Answered By - TSCAmerica.com

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Hilt Testing - Replace internal Hilt-Module in separate Android multi-module app

Issue

I have an Android app where the codebase is split into 2 different modules: App and Domain

Goal: I am attempting to use the Hilt provided testing functionality to replace a Domain internal dependency when creating App tests.

In Domain, I have an internal interface with an internal implementation, like below:

internal interface Database {
    fun add(value: String)
}

internal class DatabaseImpl @Inject constructor() : Database {
    override fun add(value: String) { ... }
}

The above guarantees that the Database can only be used inside Domain and cannot be accessed from elsewhere.

In Domain I have another interface (which is not internal), for use in App, with an internal implementation, like below:

interface LoginService {
    fun userLogin(username: String, password: String)
}

internal class LoginServiceImpl @Inject constructor(database: Database) {
    override fun userLogin(username: String, password: String) {
        // Does something with the Database in here
    }
}

In Domain I use Hilt to provide dependencies to App, like below:

@Module(includes = [InternalDomainModule::class]) // <- Important. Allows Hilt access to the dependencies provided by InternalDomainModule.
@InstallIn(SingletonComponent::class)
class DomainModule {
   ...
}

@Module
@InstallIn(SingletonComponent::class)
internal class InternalDomainModule {

    @Provides
    @Singleton
    fun provideDatabase() : Database = DatabaseImpl()

    @Provides
    @Singleton
    fun provideLoginService(database: Database) : LoginService = LoginServiceImpl(database)
}

This all works perfectly in isolating my implementations and only exposes a single interface outside of Domain.

However, when I need to provide fake implementations inside App using the Hilt guidelines, I am unable to replace the LoginService as I do not have access to InternalDomainModule (because it is internal to Domain only) and replacing DomainModule does not replace LoginService (as it is provided in another Hilt module, namely InternalDomainModule), like below:

@Module
@TestInstallIn(
    components = [SingletonComponent::class],
    replaces = [DomainModule::class] // [InternalDomainModule::class] is impossible as inaccessible in **App**
)
class FakeModule {

    @Provides
    @Singleton
    fun provideFakeLoginService() : LoginService = FakeLoginServiceImpl() <- Something fake
}

The above leads to only DomainModule being replaced, not InternalDomainModule, which leads to LoginService being provided twice, which makes Hilt unhappy.

Making things not internal to Domain fixes the issue, but defeats the purpose of having a multi-module Android app with clear separations.

Solution

Solution 1:

I would make the internal LoginService in some way different for Dagger than the public one. For example, add a qualifier to it:

@Module(includes = [InternalDomainModule::class])
@InstallIn(SingletonComponent::class)
class DomainModule {

    @Provides
    @Singleton
    fun provideLoginService(
        @Named("Internal") internalLoginService: LoginService
    ) : LoginService = internalLoginService
}

@Module
@InstallIn(SingletonComponent::class)
internal class InternalDomainModule {

    @Provides
    @Singleton
    fun provideDatabase() : Database = DatabaseImpl()

    @Provides
    @Singleton
    @Named("Internal")
    fun provideLoginService(database: Database) : LoginService = LoginServiceImpl(database)
}

This way, it won't be duplicated in tests.

Solution 2:

Even better, you could implement a LoginServiceFactory:

interface LoginServiceFactory {
    fun create(): LoginService
}

internal class LoginServiceFactoryImpl @Inject constructor(
    private val database: Database
) : LoginServiceFactory {
    override fun create(): LoginService =
        LoginServiceImpl(database)
}

Then your modules would look like this:

@Module(includes = [InternalDomainModule::class])
@InstallIn(SingletonComponent::class)
class DomainModule {

    @Provides
    @Singleton
    fun provideLoginService(loginServiceFactory: LoginServiceFactory) : LoginService =
        loginServiceFactory.create()
}

@Module
@InstallIn(SingletonComponent::class)
internal class InternalDomainModule {

    @Provides
    @Singleton
    fun provideDatabase() : Database = DatabaseImpl()

    @Provides
    @Singleton
    fun provideLoginServiceFactory(database: Database) : LoginServiceFactory =
        LoginServiceFactoryImpl(database)
}

Answered By - Slav

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Issue with empty queryProductDetailsAsync

Issue

I have an issue retrieving product details, I have setup in my google play console this way:

my google play config

And I have done the following:

myLog("MYAPP-TEST---1")
val purchasesUpdatedListener =
    PurchasesUpdatedListener { billingResult, purchases ->
        if (billingResult.responseCode ==
            BillingClient.BillingResponseCode.OK
            && purchases != null
        ) {
            for (purchase in purchases) {
                // Process the purchases
                myLog("MYAPP-TEST---")
            }
        } else if (billingResult.responseCode ==
            BillingClient.BillingResponseCode.USER_CANCELED
        ) {
            myLog("MYAPP-TEST---2")
            // Purchase cancelled by user
        } else {
            myLog("MYAPP-TEST---3")
            // Handle errors here
        }
    }

var billingClient = BillingClient.newBuilder(this)
    .setListener(purchasesUpdatedListener)
    .enablePendingPurchases()
    .build()

billingClient.startConnection(object : BillingClientStateListener {
    override fun onBillingSetupFinished(billingResult: BillingResult) {
        if (billingResult.responseCode == BillingClient.BillingResponseCode.OK) {
            // Connection successful
            myLog("MYAPP-TEST---SUCCESS")
        } else {
            // Connection failed
        }
    }

    override fun onBillingServiceDisconnected() {
        // Connection to billing service lost
        myLog("MYAPP-TEST---DISCONNECTED")
    }
})


val productList: ArrayList<Product> = ArrayList()
productList.add(
    Product.newBuilder()
        .setProductId("poroductid1")
        .setProductType(BillingClient.ProductType.SUBS)
        .build()
);
productList.add(
    Product.newBuilder()
        .setProductId("poroductid2")
        .setProductType(BillingClient.ProductType.SUBS)
        .build()
);
productList.add(
    Product.newBuilder()
        .setProductId("poroductid3")
        .setProductType(BillingClient.ProductType.SUBS)
        .build()
);
productList.add(
    Product.newBuilder()
        .setProductId("poroductid4")
        .setProductType(BillingClient.ProductType.SUBS)
        .build()
);

val queryProductDetailsParams =
    QueryProductDetailsParams.newBuilder()
        .setProductList(productList)
        .build()

processPurchases()

billingClient.queryProductDetailsAsync(queryProductDetailsParams) { billingResult,
                                                                     skuDetailsList ->
    if (skuDetailsList.isNotEmpty()) {
        for (productDet in skuDetailsList) {
            myLog("MYAPP-TEST----")
            myLog(productDet.name)
        }
        // Process list of matching products
    } else {

        myLog("MYAPP-TEST---No product matches found")
        // No product matches found
    }
    // Process the result
}

And I keep getting those debugs

2022-09-16 16:04:17.983 13457-13457/com.my.app D/MainActivity: MYAPP-TEST---1

2022-09-16 16:04:18.012 13457-13457/com.my.app D/MainActivity: MYAPP-TEST---No product matches found

2022-09-16 16:04:18.470 13457-13700/com.my.app D/MainActivity: MYAPP-TEST---SUCCESS

I also have publish my app so products should be "publicly" available (don't know if it is still needed, but I seen elsewhere it was).

So has you can see my product details request seams to be empty.

I am pretty new in kotlin / app developpement so I will probably need a lot of explaining.

Solution

Your setup succeeds after trying to retrieve the product list. You want to be sure that the setup succeeds before.

And this is what BillingClientStateListener is for.

First you should put all your products retrieval code in a separate function :

fun retrieveProducts() {
    val productList: ArrayList<Product> = ArrayList()
productList.add(
    Product.newBuilder()
        .setProductId("poroductid1")
        .setProductType(BillingClient.ProductType.SUBS)
        .build()
);
productList.add(
    Product.newBuilder()
        .setProductId("poroductid2")
        .setProductType(BillingClient.ProductType.SUBS)
        .build()
);
productList.add(
    Product.newBuilder()
        .setProductId("poroductid3")
        .setProductType(BillingClient.ProductType.SUBS)
        .build()
);
productList.add(
    Product.newBuilder()
        .setProductId("poroductid4")
        .setProductType(BillingClient.ProductType.SUBS)
        .build()
);

val queryProductDetailsParams =
    QueryProductDetailsParams.newBuilder()
        .setProductList(productList)
        .build()

billingClient.queryProductDetailsAsync(queryProductDetailsParams) { billingResult,
                                                                     skuDetailsList ->
    if (skuDetailsList.isNotEmpty()) {
        for (productDet in skuDetailsList) {
            myLog("MYAPP-TEST----")
            myLog(productDet.name)
        }
        // Process list of matching products
    } else {

        myLog("MYAPP-TEST---No product matches found")
        // No product matches found
    }
    // Process the result
}

Afterwards, call your function in the BillingClientStateListener onBillingSetupFinished function :

billingClient.startConnection(object : BillingClientStateListener {
    override fun onBillingSetupFinished(billingResult: BillingResult) {
        if (billingResult.responseCode == BillingClient.BillingResponseCode.OK) {
            // Connection successful
            myLog("MYAPP-TEST---SUCCESS")
            // This is where you can start retrieving your products
            retrieveProducts()
        } else {
            // Connection failed
        }
    }

    override fun onBillingServiceDisconnected() {
        // Connection to billing service lost
        myLog("MYAPP-TEST---DISCONNECTED")
    }
})

The problem you faced is due to asynchronous actions : both your client setup and your purchases retrieval are asynchronous, meaning that they aren't executed on the same thread that your basic code.

To be sure to do things in the good order, you have to use those listeners the Billing library provides you with !

First, you want to setup your billing service. When done, the onBillingSetupFinished callback is called. That's when you are sure you can go further !

This is a classical "problem" you will have to face in Android development, and the listeners system is a classical way of doing actions resulting from another action done in another thread than the main thread.

Answered By - Jeremy F

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Parse string date to millis in kotlin

Issue

I am using SDF to parse a string date to millis with below code

private fun dateToMilliseconds(dateValue: String): Long? {
val sdf = SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS")
val date: Date
try {
    date = sdf.parse(dateValue)!!
    return date.time
} catch (e: Exception) {
    e.printStackTrace()
}
return null
}

And the date is val pdt = "2024-01-17T20:14:29.819Z"

On running it in android I get the exception for unparseable date

java.text.ParseException: Unparseable date: "2024-01-17T20"

Solution

I used your code in IntellijIdea and Android Studio and it works properly. Make sure you imported below classes and not using other same name classes:

import java.text.SimpleDateFormat
import java.util.*

Answered By - Hossein Shahmohammadi

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Kotlin Generics with upper and lower bounds required

Issue

I come across a generics problem that I'm struggling with. I've distilled the code down to a simple example to show the problem, as follows

I have a simple hierarchy of types:

open class Fruit
class Apple : Fruit() {
    fun crunch(): String = "CRUNCH!"
}

class Orange : Fruit() {
    fun squish(): String = "SQUISH!"
}

and a corresponding hierarchy of consumers specific to those types, with a generic parent:

abstract class FruitConsumer<T : Fruit> {
    abstract fun consume(fruit: T)
}

class AppleConsumer : FruitConsumer<Apple>() {
    override fun consume(apple: Apple) {
        println("consuming apple ${apple.crunch()}")
    }
}

class OrangeConsumer : FruitConsumer<Orange>() {
    override fun consume(orange: Orange) {
        println("consuming orange ${orange.squish()}")
    }
}

I need to be able to process a list of fruit of unknown type using one of these 'consumers' and currently have this:

fun processFruit(fruitList: List<Fruit>) {
    fruitList.forEach {
        val processor = consumerFactory(it)
        processor.consume(it)
    }
}

fun <T : Fruit> consumerFactory(theFruit: T): FruitConsumer<T> {
    return when (theFruit) {
        is Apple -> AppleConsumer() as FruitConsumer<T>       <---- unchecked cast
        is Orange -> OrangeConsumer() as FruitConsumer<T>     <---- unchecked cast
        else -> throw RuntimeException()
    }
}

This reports unchecked casts for as FruitConsumer<T>, but removing these means I have to consider bounds. This then comes with its own problems, e.g.

If I define the return of the factory method as an 'out' type (making it a 'producer' to the kotlin compiler), I don't need the casts:

fun processFruit(fruitList: List<Fruit>) {
    fruitList.forEach {
        val processor = consumerFactory(it)
        processor.consume(it)         <--- ERROR HERE
    }
}

fun <T : Fruit> consumerFactory(theFruit: T): FruitConsumer<out Fruit> {
    return when (theFruit) {
        is Apple -> AppleConsumer()      <--- no cast
        is Orange -> OrangeConsumer()    <--- no cast
        else -> throw RuntimeException()
    }
}

but then since the return type from the factory is considered a producer, it can't consume anything.

If I change the bounds using the 'in' keyword (to make the return type a 'consumer' to the kotlin compiler), then I can't return the specific consumer types:

fun processFruit(fruitList: List<Fruit>) {
    fruitList.forEach {
        val processor = consumerFactory(it)
        processor.consume(it)      <------ This compiles fine now
    }
}

fun <T : Fruit> consumerFactory(theFruit: T): FruitConsumer<in Fruit> {
    return when (theFruit) {
        is Apple -> AppleConsumer()         <--- Error type mismatch
        is Orange -> OrangeConsumer()       <--- Error type mismatch
        else -> throw RuntimeException()
    }
}

Am I missing something obvious here? Is there an elegant solution to this without using unchecked casts?

Solution

This is achievable in a type-safe fashion by:

1. Completing the action on a Fruit without returning the respective FruitConsumer
2. Defining a method on Fruit for the functionality, or
3. Using a visitor pattern to locate the functionality in one place.

Completing the action without returning

Here, you can adjust your loop to:

fun processFruit(fruitList: List<Fruit>) {
    fruitList.forEach {
        consumeFruit(it)
    }
}

fun consumeFruit(theFruit: Fruit) {
    return when (theFruit) {
        is Apple -> AppleConsumer().consume(theFruit)
        is Orange -> OrangeConsumer().consume(theFruit)
        else -> throw RuntimeException()
    }
}

By not returning we have not given ourselves the burden of having two compatible objects together 'in the wild'; then we can write a program that compiles fine¹.

In addition, there are two other ways that are worthy of consideration in such a situation (although they are essentially using the same theme).

A method on Fruit

This is probably the most straightforward way, and is really classic OOP and the Hollywood principle². Programs normally simplify when you locate functionality for the same 'thing' in the same place.

Here, define:

abstract class Fruit {
    abstract fun beConsumed()
}

Then you can have on each Fruit:

class Apple : Fruit() {
    fun crunch(): String = "CRUNCH!"
    override fun beConsumed() {
        AppleConsumer().consume(this)
    }
}

class Orange : Fruit() {
    fun squish(): String = "SQUISH!"
    override fun beConsumed() {
        OrangeConsumer().consume(this)
    }
}

And your loop simply becomes:

fun processFruit(fruitList: List<Fruit>) {
    fruitList.forEach {
        it.beConsumed()
    }
}

Using a visitor pattern

It may not be possible for each Fruit to know how it is consumed, or it may be inappropriate for other reasons. Such situations could be when the FruitConsumer needs various dependencies³ or is in a different module.

Then the visitor pattern nicely still allows a type-safe approach. First we need to require Fruits to accept visitors:

abstract class Fruit {
    abstract fun accept(visitor: FruitVisitor)
}

interface FruitVisitor {
    fun visit(apple: Apple)
    fun visit(orange: Orange)
}

We define our accept methods in the usual way:

class Apple : Fruit() {
    fun crunch(): String = "CRUNCH!"
    override fun accept(visitor: FruitVisitor) = visitor.visit(this)
}

class Orange : Fruit() {
    fun squish(): String = "SQUISH!"
    override fun accept(visitor: FruitVisitor) = visitor.visit(this)
}

Then a visitor is given the knowledge of how to consume the different Fruit types:

class FruitConsumerVisitor : FruitVisitor {
    override fun visit(apple: Apple) {
        AppleConsumer().consume(apple)
    }

    override fun visit(orange: Orange) {
        OrangeConsumer().consume(orange)
    }
}

And finally we update our loop:

fun processFruit(fruitList: List<Fruit>) {
    val fruitVisitor = FruitConsumerVisitor()
    fruitList.forEach {
        it.accept(fruitVisitor)
    }
}

To wrap it up, I've put this solution on a Kotlin playground with a main method so we can see it in action:

fun main() {
    processFruit(listOf(Apple(), Orange(), Apple()))
}

// Prints:
// consuming apple CRUNCH!
// consuming orange SQUISH!
// consuming apple CRUNCH!

---

¹For completeness, you might consider improving this further by making Fruit a sealed class to avoid the else in the when. If this is not possible, then one of the other methods is more appropriate as the compiler will not allow you to extend the Fruit family without prescribing how the new fruit is consumed.

²"Don't call us, we'll call you"

³Although that could be overcome by passing in the dependencies needed to construct any FruitConsumer instance in the beConsumed method.

Answered By - Simon Jacobs

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Navigation with Arguments with Jetpack Compose

Issue

I've been troubleshooting this issue for couple of days now about navigating with args in jetpack compose. I feel like I'm missing something simple, really simple that I can't figure out somehow. I tried making sure I'm coding it correctly but to no avail I still get the error.

So the error: Navigation destination that matches request NavDeepLinkRequest{ uri=android-app://androidx.navigation/second_screen/Item Six } cannot be found in the navigation graph NavGraph(0x0) startDestination={Destination(0x442b361f) route=home_screen}

I feel like I'm done everything correct but still cant get through this error. Or there is something simple that I'm missing.

My NavHost:

interface NavigationDestination{
    val route: String
}

@Composable
fun MainNavHost(
){
    val navController = rememberNavController()
    NavHost(
        navController = navController,
        startDestination = HomeScreenNavigation.route,
    ){
        composable(HomeScreenNavigation.route){
            HomeScreen(onItemClick = {nameString->
                    navController.navigate("${SecondNavigationDestination.route}/${nameString}")
                        {
                            launchSingleTop = true
                        }
            })
        }
        composable(
            route = SecondNavigationDestination.routeWithArg,
            arguments = listOf(navArgument(SecondNavigationDestination.nameArg)
            {type = NavType.StringType})
        ){
            SecondScreen()
        }
    }
}

My Screens

First Screen:

object HomeScreenNavigation: NavigationDestination{
    override val route = "home_screen"
}

@Composable
fun HomeScreen(
    modifier: Modifier = Modifier,
    onItemClick: (String) -> Unit
){
    ItemList(
        itemList = LocalData.itemList,
        onItemClick = onItemClick
    )
}

@Composable
fun ItemList(
    itemList: List<ItemModel>,
    onItemClick: (String) -> Unit,
    modifier: Modifier = Modifier
){
    LazyColumn(
        verticalArrangement = Arrangement.spacedBy(9.dp)
    ){
        items(
            items = itemList,
            key = {it.id}
        ){
            Item(
                item = it,
                onItemClick = onItemClick
            )
        }
    }
}

@Composable
fun Item(
    item: ItemModel,
    modifier: Modifier = Modifier,
    onItemClick: (String) -> Unit
){
    Row(
        modifier = modifier
            .fillMaxWidth()
            .padding(9.dp)
            .clickable { onItemClick(item.name) },
        horizontalArrangement = Arrangement.Center,
        verticalAlignment = Alignment.Top
    ){
    Text(
        text = item.name
    )
    }
}

/////////////////////////////////////////////////////// Second Screen:

object SecondNavigationDestination: NavigationDestination{
    override val route = "second_screen"
    const val nameArg = "nameArg"
    val routeWithArg = "${route}/$nameArg"
}

@Composable
fun SecondScreen(
){
    val viewModel: MainViewModel = viewModel()
    Box(
    contentAlignment = Alignment.Center
    ){
        Text(
            viewModel.id
        )
    }
}

///////////////////////////////////////////////// ViewModel:

class MainViewModel(
    savedStateHandle: SavedStateHandle
): ViewModel(){
    val id: String = savedStateHandle[SecondNavigationDestination.nameArg] ?: "empty"
}

Solution

Change this

val routeWithArg = "${route}/$nameArg"

to this

val routeWithArg = "${route}/{$nameArg}"

For more info: docs

Answered By - Javlon

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How to make an edittext inside NestedScrollView have height = "parent"

Issue

I want the Edittext to have a height equal to the full height of the NestedScrollView, but I don't know how to do it

        <androidx.core.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintTop_toBottomOf="@id/et_title"
        app:layout_constraintBottom_toBottomOf="parent">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">
            <LinearLayout
                android:id="@+id/ll_contain_rv"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:layout_constraintTop_toBottomOf="@id/et_title"
                android:orientation="vertical"
                android:visibility="gone">

                <androidx.recyclerview.widget.RecyclerView
                    android:id="@+id/rv_checklist"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
                    android:orientation="vertical"
                    android:visibility="visible"/>

                <LinearLayout
                    android:id="@+id/ll_add_checklist"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal"
                    android:background="?attr/selectableItemBackground"
                    android:paddingEnd="@dimen/_80sdp"
                    android:alpha="0.7">

                    <androidx.appcompat.widget.AppCompatImageView
                        android:id="@+id/iv_add"
                        android:layout_width="@dimen/_30sdp"
                        android:layout_height="@dimen/_30sdp"
                        android:padding="@dimen/_5sdp"
                        android:scaleType="fitCenter"
                        app:tint="@color/black"
                        android:src="@drawable/ic_add"/>

                    <androidx.appcompat.widget.AppCompatTextView
                        android:id="@+id/tv_add"
                        android:layout_width="wrap_content"
                        android:layout_height="match_parent"
                        android:layout_marginStart="@dimen/_5sdp"
                        style="@style/AppTheme.TextView.Content_Note"
                        android:gravity="center_vertical"
                        android:text="@string/text_add_item"/>

                </LinearLayout>
            </LinearLayout>
            <com.sophimp.are.RichEditText
                android:id="@+id/et_content"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:background="@android:color/transparent"
                android:layout_marginTop="@dimen/_5sdp"
                android:hint="@string/text_notes_here"
                android:inputType="textMultiLine|textNoSuggestions"
                style="@style/AppTheme.TextView.Content_Note"
                android:gravity="top"
                android:lineSpacingExtra="4dp"
                android:visibility="visible"/>

        </LinearLayout>
    </androidx.core.widget.NestedScrollView>

This is an image of the NestedScrollView's scope[enter image description here][1]

This is an image of the scope of Edittext[enter image description here][2] [1]: https://i.stack.imgur.com/Ca674.png [2]: https://i.stack.imgur.com/3TG3N.png

I want the Edittext to take up the remaining height of the NestedScrollView

Solution

I found the way, just in NestedScrollView set "android:fillViewport="true"" and in Edittext set " android:layout_height="match_parent""

Answered By - DucK

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INTELLIJ IDEA Build Output Error : Cannot access 'java.io.Serializable' which is a supertype of 'kotlin.String'

Issue

I recently installed Intellj Idea Community Edition for learning Kotlin: since I'm a Beginner I write some basic code which is as follows:

 fun main() {
        val x = readln().toString();
    
        println(x);
    }

I don't know if there are some spelling mistakes, and yeah I hit the run button to let the build process start during the compilation, the build output showed this message:

Kotlin: Cannot access 'java.io.Serializable' which is a supertype of 'kotlin.String'. Check your module classpath for missing or conflicting dependencies[enter image description here]

This is my project Structure modules snapshot:

and this is my project libraries: and my project setting :

I'm expecting to get this problem solved thanks in advance

Solution

ok, I think you have set java development Kit for you project so that the IDE can access all of the classes and tools that are needed to run your project correctly.

simply walk through these steps: File > Project Structure > Project Setting > Project > SDK > Edit button > here you have to locate your JDK main folder

Answered By - Bilal Bilal

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Unresolved reference: ExpandLess

Issue

Iam complete new to Kotlin and to Jetpack Compose i have made the Jetpack Compose basics (CodeAlong) and at the end it keeps saying Unresolved reference Expandless ore Unresolved reference: ExpandMore. Can someone help me find the Right thing?!

I searched a bit but my Knowledge isn't big enough to find an answerenter image description here

Solution

There might be an import for Icons.Filled missing. Please try to change your code to:

imageVector = if (expanded) Icons.Filled.ExpandLess else Icons.Filled.ExpandMore

If that does not resolve your issue, check the dependencies in your module's build.gradle file and try to add the following line:

implementation "androidx.compose.material:material-icons-extended:1.5.4"

If Android Studio asks to to synchronize the Gradle files, click okay.

Answered By - BenjyTec

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Jetpack compose preview crashes with hiltViewModel<>()

Issue

I use compose version 1.1.0-beta03 and hilt-navigation-compose:1.0.0-beta01. this is my Composable code:

fun EngagementBotChart(modifier: Modifier = Modifier) {
    val newHomeViewModel = hiltViewModel<HomeViewModel>()
    AndroidView(
        modifier = modifier.fillMaxSize(),
        factory = { context ->
            
        },
        update = { view ->
            
        }
    )
}

it works fine when I build the project but this is what occurs in compose preview:

java.lang.NoSuchMethodException: ir.inbo.app.home.viewmodel.HomeViewModel.<init>()
    at java.base/java.lang.Class.getConstructor0(Class.java:3349)
    at java.base/java.lang.Class.newInstance(Class.java:556)
    at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:219)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
    at androidx.lifecycle.viewmodel.compose.ViewModelKt.get(ViewModel.kt:87)
    at androidx.lifecycle.viewmodel.compose.ViewModelKt.viewModel(ViewModel.kt:72)
    at ir.inbo.app.home.ui.HomeComponentsKt.EngagementBotChart(HomeComponents.kt:281)
    at ir.inbo.app.home.ui.ComposableSingletons$HomeComponentsKt$lambda-1$1$1$4$invoke$$inlined$ConstraintLayout$2.invoke(ConstraintLayout.kt:2424)
    at ir.inbo.app.home.ui.ComposableSingletons$HomeComponentsKt$lambda-1$1$1$4$invoke$$inlined$ConstraintLayout$2.invoke(ConstraintLayout.kt:101)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.ui.layout.LayoutKt.MultiMeasureLayout(Layout.kt:562)
    at ir.inbo.app.home.ui.ComposableSingletons$HomeComponentsKt$lambda-1$1$1$4.invoke(HomeComponents.kt:255)
    at ir.inbo.app.home.ui.ComposableSingletons$HomeComponentsKt$lambda-1$1$1$4.invoke(HomeComponents.kt:86)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:116)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at ir.inbo.app.home.ui.HomeComponentsKt.HomeBoxComponent(HomeComponents.kt:267)
    at ir.inbo.app.home.ui.ComposableSingletons$HomeComponentsKt$lambda-1$1$invoke$$inlined$ConstraintLayout$2.invoke(ConstraintLayout.kt:2413)
    at ir.inbo.app.home.ui.ComposableSingletons$HomeComponentsKt$lambda-1$1$invoke$$inlined$ConstraintLayout$2.invoke(ConstraintLayout.kt:101)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.ui.layout.LayoutKt.MultiMeasureLayout(Layout.kt:562)
    at ir.inbo.app.home.ui.ComposableSingletons$HomeComponentsKt$lambda-1$1.invoke(HomeComponents.kt:255)
    at ir.inbo.app.home.ui.ComposableSingletons$HomeComponentsKt$lambda-1$1.invoke(HomeComponents.kt:34)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.material.MaterialTheme_androidKt.PlatformMaterialTheme(MaterialTheme.android.kt:23)
    at androidx.compose.material.MaterialThemeKt$MaterialTheme$1$1.invoke(MaterialTheme.kt:82)
    at androidx.compose.material.MaterialThemeKt$MaterialTheme$1$1.invoke(MaterialTheme.kt:81)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.runtime.CompositionLocalKt.CompositionLocalProvider(CompositionLocal.kt:228)
    at androidx.compose.material.TextKt.ProvideTextStyle(Text.kt:265)
    at androidx.compose.material.MaterialThemeKt$MaterialTheme$1.invoke(MaterialTheme.kt:81)
    at androidx.compose.material.MaterialThemeKt$MaterialTheme$1.invoke(MaterialTheme.kt:80)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.runtime.CompositionLocalKt.CompositionLocalProvider(CompositionLocal.kt:228)
    at androidx.compose.material.MaterialThemeKt.MaterialTheme(MaterialTheme.kt:72)
    at ir.inbo.app.theme.ThemeKt.InboTheme(Theme.kt:54)
    at ir.inbo.app.home.ui.HomeComponentsKt.HomeGrid(HomeComponents.kt:34)
    at ir.inbo.app.home.ui.HomeComponentsKt.HomeGridPreview(HomeComponents.kt:232)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at androidx.compose.ui.tooling.CommonPreviewUtils.invokeComposableMethod(CommonPreviewUtils.kt:150)
    at androidx.compose.ui.tooling.CommonPreviewUtils.invokeComposableViaReflection$ui_tooling_release(CommonPreviewUtils.kt:189)
    at androidx.compose.ui.tooling.ComposeViewAdapter$init$3$1$composable$1.invoke(ComposeViewAdapter.kt:578)
    at androidx.compose.ui.tooling.ComposeViewAdapter$init$3$1$composable$1.invoke(ComposeViewAdapter.kt:576)
    at androidx.compose.ui.tooling.ComposeViewAdapter$init$3$1.invoke(ComposeViewAdapter.kt:615)
    at androidx.compose.ui.tooling.ComposeViewAdapter$init$3$1.invoke(ComposeViewAdapter.kt:571)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.runtime.CompositionLocalKt.CompositionLocalProvider(CompositionLocal.kt:228)
    at androidx.compose.ui.tooling.InspectableKt.Inspectable(Inspectable.kt:61)
    at androidx.compose.ui.tooling.ComposeViewAdapter$WrapPreview$1.invoke(ComposeViewAdapter.kt:520)
    at androidx.compose.ui.tooling.ComposeViewAdapter$WrapPreview$1.invoke(ComposeViewAdapter.kt:519)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.runtime.CompositionLocalKt.CompositionLocalProvider(CompositionLocal.kt:228)
    at androidx.compose.ui.tooling.ComposeViewAdapter.WrapPreview(ComposeViewAdapter.kt:515)
    at androidx.compose.ui.tooling.ComposeViewAdapter.access$WrapPreview(ComposeViewAdapter.kt:121)
    at androidx.compose.ui.tooling.ComposeViewAdapter$init$3.invoke(ComposeViewAdapter.kt:571)
    at androidx.compose.ui.tooling.ComposeViewAdapter$init$3.invoke(ComposeViewAdapter.kt:568)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.ui.platform.ComposeView.Content(ComposeView.android.kt:410)
    at androidx.compose.ui.platform.AbstractComposeView$ensureCompositionCreated$1.invoke(ComposeView.android.kt:252)
    at androidx.compose.ui.platform.AbstractComposeView$ensureCompositionCreated$1.invoke(ComposeView.android.kt:251)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.runtime.CompositionLocalKt.CompositionLocalProvider(CompositionLocal.kt:228)
    at androidx.compose.ui.platform.CompositionLocalsKt.ProvideCommonCompositionLocals(CompositionLocals.kt:166)
    at androidx.compose.ui.platform.AndroidCompositionLocals_androidKt$ProvideAndroidCompositionLocals$3.invoke(AndroidCompositionLocals.android.kt:123)
    at androidx.compose.ui.platform.AndroidCompositionLocals_androidKt$ProvideAndroidCompositionLocals$3.invoke(AndroidCompositionLocals.android.kt:122)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.runtime.CompositionLocalKt.CompositionLocalProvider(CompositionLocal.kt:228)
    at androidx.compose.ui.platform.AndroidCompositionLocals_androidKt.ProvideAndroidCompositionLocals(AndroidCompositionLocals.android.kt:114)
    at androidx.compose.ui.platform.WrappedComposition$setContent$1$1$3.invoke(Wrapper.android.kt:157)
    at androidx.compose.ui.platform.WrappedComposition$setContent$1$1$3.invoke(Wrapper.android.kt:156)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.runtime.CompositionLocalKt.CompositionLocalProvider(CompositionLocal.kt:228)
    at androidx.compose.ui.platform.WrappedComposition$setContent$1$1.invoke(Wrapper.android.kt:156)
    at androidx.compose.ui.platform.WrappedComposition$setContent$1$1.invoke(Wrapper.android.kt:140)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:107)
    at androidx.compose.runtime.internal.ComposableLambdaImpl.invoke(ComposableLambda.jvm.kt:34)
    at androidx.compose.runtime.ComposerKt.invokeComposable(Composer.kt:3337)
    at androidx.compose.runtime.ComposerImpl$doCompose$2$5.invoke(Composer.kt:2582)
    at androidx.compose.runtime.ComposerImpl$doCompose$2$5.invoke(Composer.kt:2571)
    at androidx.compose.runtime.SnapshotStateKt__DerivedStateKt.observeDerivedStateRecalculations(DerivedState.kt:234)
    at androidx.compose.runtime.SnapshotStateKt.observeDerivedStateRecalculations(Unknown Source)
    at androidx.compose.runtime.ComposerImpl.doCompose(Composer.kt:2571)
    at androidx.compose.runtime.ComposerImpl.composeContent$runtime_release(Composer.kt:2522)
    at androidx.compose.runtime.CompositionImpl.composeContent(Composition.kt:478)
    at androidx.compose.runtime.Recomposer.composeInitial$runtime_release(Recomposer.kt:748)
    at androidx.compose.runtime.CompositionImpl.setContent(Composition.kt:433)
    at androidx.compose.ui.platform.WrappedComposition$setContent$1.invoke(Wrapper.android.kt:140)
    at androidx.compose.ui.platform.WrappedComposition$setContent$1.invoke(Wrapper.android.kt:131)
    at androidx.compose.ui.platform.AndroidComposeView.setOnViewTreeOwnersAvailable(AndroidComposeView.android.kt:897)
    at androidx.compose.ui.platform.WrappedComposition.setContent(Wrapper.android.kt:131)
    at androidx.compose.ui.platform.WrappedComposition.onStateChanged(Wrapper.android.kt:182)
    at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:354)
    at androidx.lifecycle.LifecycleRegistry.addObserver(LifecycleRegistry.java:196)
    at androidx.compose.ui.platform.WrappedComposition$setContent$1.invoke(Wrapper.android.kt:138)
    at androidx.compose.ui.platform.WrappedComposition$setContent$1.invoke(Wrapper.android.kt:131)
    at androidx.compose.ui.platform.AndroidComposeView.onAttachedToWindow(AndroidComposeView.android.kt:984)
    at android.view.View.dispatchAttachedToWindow(View.java:20479)
    at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:3489)
    at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:3496)
    at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:3496)
    at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:3496)
    at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:3496)
    at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:3496)
    at android.view.AttachInfo_Accessor.setAttachInfo(AttachInfo_Accessor.java:44)
    at com.android.layoutlib.bridge.impl.RenderSessionImpl.inflate(RenderSessionImpl.java:360)
    at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:431)
    at com.android.tools.idea.layoutlib.LayoutLibrary.createSession(LayoutLibrary.java:141)
    at com.android.tools.idea.rendering.RenderTask.createRenderSession(RenderTask.java:714)
    at com.android.tools.idea.rendering.RenderTask.lambda$inflate$7(RenderTask.java:870)
    at com.android.tools.idea.rendering.RenderExecutor$runAsyncActionWithTimeout$2.run(RenderExecutor.kt:187)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:834)

when I delete the hiltviewModel code everything work fine! I try it with different versions of compose and I can't solve this problem!

Solution

After some searching and reviewing of google sample codes here is the way you must follow to prevent the preview crashes:

Have a root composable for your screen and initial view model there, collect your data from viewModel as state (in case your data is flow) then pass data to content composable

@Composable
fun HomeScreen(
    navController: NavController
){
    val viewModel = hiltViewModel<HomeViewModel>()
    val someData by viewModel.someData.collectAsState()
}

@Composable
fun HomeScreenContent(
    someData: Type = defaultvalue
){
   //your UI codes
}

in preview use, HomeScreenContent instead of HomeScreen, and your problem will be solved!

thanks to @PhilipDukhov that helped in the comments

Answered By - Mobin Yardim

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The project is using an incompatible version (AGP 8.2.1) of the Android Gradle plugin. Latest supported version is AGP 8.2.0-alpha14

Issue

I'm encountering an issue with Android Gradle Plugin (AGP) version in my project. Currently, I am using AGP 8.2.1, but its seems to be incompatible. The error message says that the latest supported version is AGP 8.2.0-alpha14.

[Error] Incompatible AGP Version: The project is using AGP 8.2.1, but the latest supported version is AGP 8.2.0-alpha14.

Tried syncing gradle

Solution

Solved by downgrading gradle version in the libs.versions.toml file, in my case, I downgraded it to "8.1.0".

Thanks.

Answered By - Oyindamola Gideon Olarewaju

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IntellIJ IDEA Kotlin - Expecting an element

Issue

I am new to Kotlin and am now struggling with unit testing my code.

I am trying to mock the restTemplate that uses an array in the exchange method. I found that the correct way to do that would be

ArgumentMatchers.<ParameterizedTypeReference<Array<DataDto>>>any()

however compiler throws an error saying Expecting an element and doesn't allow me to qualify the type for any(). Is there any setting for IDEA to fix this compiler error?

I use Java 17 as the SDK, but I tried it Kotlin SDK 1.6.10 as well.

Solution

type arguments go after the function name (and before the ()), not before so you need to use

ArgumentMatchers.any<ParameterizedTypeReference<Array<DataDto>>>()

Answered By - Ivo

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Android app sometimes recreates the entire Activity on launch

Issue

I'm currently working on a small project that uses DataStore<Preferences> to save some data. At seemingly random times, when I would uninstall and reinstall the app, I would get the exception: java.lang.IllegalStateException: There are multiple DataStores active for the same file

This is the relevant code:

class MainActivity : ComponentActivity() {

    private lateinit var appControllerSettings: AppControllerSettings

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        lifecycleScope.launch {
            appControllerSettings = AppControllerSettings.getInstance(this@MainActivity)
        }
    }
}

class AppControllerSettings private constructor(context: Context) {

    companion object {
        private val USERS_KEY = stringSetPreferencesKey("users")
        private val mutex = Mutex()
        private var instance: AppControllerSettings? = null

        /**
         * Return the singleton instance of [AppControllerSettings]
         * */
        suspend fun getInstance(context: Context): AppControllerSettings {
            return instance ?: mutex.withLock {
                instance ?: AppControllerSettings(context).apply {
                    try {
                        val preferences = withContext(Dispatchers.IO) {
                            preferencesStore.data.first()
                        }
                        val userIds: Set<String>? = preferences[USERS_KEY]
                        if (userIds != null) {
                            users.addAll(userIds)
                        }
                    } catch (ioe: IOException) {
                        debugError("failed to read app controller settings from preferences store", ioe)
                    }

                    instance = this
                }
            }
        }
    }

    private val preferencesStore = createPreferencesStoreFromFile(context, "app_controller_settings")
    private val users: MutableSet<String> = mutableSetOf()

    suspend fun addUserToSignInHistory(user: User): Result<Unit> {
        return runCatching {
            withContext(Dispatchers.IO) {
                preferencesStore.edit { preferences ->
                    users.add(user.id)
                    preferences[USERS_KEY] = users
                }
            }
        }
    }

    fun hasUserPreviouslySignedIn(user: User): Boolean {
        return users.contains(user.id)
    }
}

I have tested the code and getInstance returns the same instance every time it is called in code, but the exception still occurs. After adding some logging statements I saw the difference between when there is a crash and when there is no crash:

Working

MainActivity class initialized
MainActivity object instance created
onCreate
AppControllerSettings.getInstance is called
AppControllerSettings class initialized
instance = null
PreferenceDataStoreFactory.create app_controller_settings
AppControllerSettings object instance created
onStart
onResume

Crashes

MainActivity class initialized
MainActivity object instance created
onCreate
AppControllerSettings.getInstance is called
AppControllerSettings class initialized
instance = null
PreferenceDataStoreFactory.create app_controller_settings
AppControllerSettings object instance created
onStart
onResume
onPause
onStop
onDestroy
MainActivity object instance created
onCreate
AppControllerSettings.getInstance is called
instance = null
onStart
onResume
PreferenceDataStoreFactory.create app_controller_settings
AppControllerSettings object instance created
java.lang.IllegalStateException: There are multiple DataStores active for the same file

I have a couple of questions about this:

1. Why is the activity sometimes being created and destroyed and created again? No screen rotation is taking place. I have gone through the process of simply installing and uninstalling the app from ADB and Android Studio over and over again, and this behavior occurs about 1 in 4 times. A few minutes before I started to write this question, the MainActivity class itself was being reinitialized, not just a new object instance created, but that behavior has now suddenly stopped.
2. Even if a new MainActivity object is being created, how is the static field instance inside of AppControllerSettings being reset to null? It's a separate class in the same file.

EDIT

This seems to at least answer question 2: https://discuss.kotlinlang.org/t/singleton-with-object-declarations-gets-garbage-collected/4786/5 The AppControllerSettings class is only initialized when it's first used and is then a candidate for garbage collection if no reference is held to it anywhere than the MainActivity which is disposed of. The only solution seems to be to initialize AppControllerSettings in a custom Application class.

Solution

I never figured out why at some times my activity is being created, destroyed and created again while simply launching the app with no other changes, but I ended up resolving my problem via the singleton pattern.

As Android doesn't give you any mechanism by which to close a DataStore, once a DataStore is opened for a given file it remains open for the lifetime of the application.

The solution was to create a DataStoreManager like this:

import android.content.Context
import androidx.datastore.core.DataStore
import androidx.datastore.preferences.core.PreferenceDataStoreFactory
import androidx.datastore.preferences.core.Preferences
import androidx.datastore.preferences.preferencesDataStoreFile

interface DataStoreManager {

    companion object {

        private val LOCK = Any()

        private var instance: DataStoreManager? = null

        fun getInstance(context: Context): DataStoreManager {
            return instance ?: synchronized(LOCK) {
                if (instance == null) {
                    instance = DataStoreManagerImpl(context)
                }
                instance!!
            }
        }
    }

    fun datastore(name: String): DataStore<Preferences>
}

private class DataStoreManagerImpl(private val context: Context) : DataStoreManager {

    private val datastores = mutableMapOf<String, DataStore<Preferences>>()

    override fun datastore(name: String): DataStore<Preferences> {
        return datastores.computeIfAbsent(name) {
            PreferenceDataStoreFactory.create {
                context.preferencesDataStoreFile(name)
                
            }
        }
    }
}

and pass that into my AppControllerSettings like so:

class AppControllerSettings private constructor(dataStoreManager: DataStoreManager) {

    companion object {

        private val USERS_KEY = stringSetPreferencesKey("users")

        private val mutex = Mutex()

        private var instance: AppControllerSettings? = null

        /**
         * Return the singleton instance of [AppControllerSettings]
         * */
        suspend fun getInstance(dataStoreManager: DataStoreManager): AppControllerSettings {
            return instance ?: mutex.withLock {
                instance ?: AppControllerSettings(dataStoreManager).apply {
                    try {
                        val preferences = withContext(Dispatchers.IO) {
                            preferencesStore.data.first()
                        }
                        val userIds: Set<String>? = preferences[USERS_KEY]
                        if (userIds != null) {
                            users.addAll(userIds)
                        }
                    } catch (ioe: IOException) {
                        debugError("failed to read app controller settings from preferences store", ioe)
                    }

                    instance = this
                }
            }
        }
    }

    private val preferencesStore = dataStoreManager.datastore("app_controller")
    private val users: MutableSet<String> = mutableSetOf()

    suspend fun addUserToSignInHistory(user: User): Result<Unit> {
        return runCatching {
            withContext(Dispatchers.IO) {
                preferencesStore.edit { preferences ->
                    users.add(user.id)
                    preferences[USERS_KEY] = users
                }
            }
        }
    }

    fun hasUserPreviouslySignedIn(user: User): Boolean {
        return users.contains(user.id)
    }
}

This way dataStoreManager.datastore(String) can be called many times, but only way DataStore will ever be created for a given name. Obvious in retrospect.

Answered By - Adam

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Micronaut is slow for the first request after startup, after that its not

Issue

I have a doubt regarding micronaut with kotlin, I created a simple api with two routes, one is for hello world and another one is for returning the received query params, when I hit any request to the web service for the first time after startup it takes around 100-200ms, but any requests after the first one takes around 10 ms. Also, request for any invalid endpoints too behaves the same, first invalid endpoint will have a spike in response time but the successive requests for unique invalid endpoints won't take long time. I have already searched it on the internet, but couldn't find useful reference. Your help would be highly appreciated :)

Video link

// micronaut controller
package com.example.controller

import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpResponse
import io.micronaut.http.MediaType
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Produces

@Controller("/api")
class HelloController {

    @Get
    @Produces(MediaType.TEXT_PLAIN)
    fun hello() = "Hello world"

    @Get("/params")
    fun getHttpParams(request: HttpRequest<*>): HttpResponse<*> {
        val params = request.parameters.asMap()
        return HttpResponse.ok(params)
    }

}

I built it using gradle shadowJar task and ran using the below command.

./gradlew optimizedJitJarAll
java -jar myapp-0.1-all-optimized.jar

1. first request after server startup to any route takes 200ms after that every route takes around 10 ms, same with 404 routes
2. I can confirm, no caching is involved here. I tested it with browser developer tools and rest api clients, every result is the same.

Solution

This is probably because of either JIT compilation, classloading and initialization, and other JVM warmup-related things such as internal optimizations and adjustments, which particularly happen during the first few requests.

These things improve performance for subsequent requests but can cause performance issues at first.

There's a general way to solve this, using something called Crac.

Answered By - Johan

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'getView' overrides nothing

Issue

I am new about android studio. I tried to use ArrayAdapter. But when i complete my codes, it says "'getView' overrides nothing".I getting this error in "return teksatirview code. this is my arrayadapter class:

package com.example.burcrehberi
import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ArrayAdapter
import kotlinx.android.synthetic.main.teksatir.view.*


class BurcArrayAdapter(
var gelencontext: Context,
resource: Int,
textViewResourceId: Int,
var burcAdlari: Array<String>,
var burcTarih: Array<String>,
var burcResimleri: Array<Int>
) : ArrayAdapter<String>(gelencontext, resource, textViewResourceId, burcAdlari) {

override fun getView(position: Int, convertView: View?, parent: ViewGroup?): View? {

    var teksatirview = convertView

    if (teksatirview == null) {

        var inflater = LayoutInflater.from(gelencontext)
        teksatirview = inflater.inflate(R.layout.teksatir, parent, false)


    }

    var burcImageView = teksatirview?.imgburcsembol
    var burcisim = teksatirview?.tvburcadi
    var burctarih = teksatirview?.tvburctarih

    burcImageView?.setImageResource(burcResimleri[position])
    burcisim?.setText(burcAdlari[position])
    burctarih?.setText(burcTarih[position])

    return teksatirview
}

}

Solution

Your problem in parent: ViewGroup?. According to signature it must be non-null type. But it's nullable in your signature, so it's completely different function in kotlin. Just change to:

 override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {

And return type View? to View too.

Answered By - Dmitrii Nechepurenko

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How do I make Gradle 8+ compile Groovy code before Kotlin code? and mix them in one project?

Issue

Using a very recent version of gradle (8.5) I want to compile Groovy code before Kotlin code. This will enable me to gradually migrate the entire project from Groovy to Kotlin using a top-down approach. (i.e., migrate one controller to Kotlin while the underlying dependencies remain in Groovy).

The Kotlin gradle plugin seems to update the task requirements, forcing the Kotlin compilation to happen first.

• Kotlin plugin wants to happen after the compileJava
• Groovy plugin wants to perform compileJava first Thus, I can't do a compileGroovy without it triggering a compileKotlin which prevents my goal from above.

TaskTree ouptut:

:compileGroovy
\--- :compileJava
     \--- :compileKotlin
          \--- :checkKotlinGradlePluginConfigurationErrors

plugins used in build.gradle:

plugins {
    id 'groovy'
    id 'application'
    id 'org.jetbrains.kotlin.jvm' version '2.0.0-Beta2'
    id "com.dorongold.task-tree" version "2.1.1"
    id 'idea'
}

Steps to reproduce:

1. place a Groovy class file in src/main/groovy (i.e., Author)
2. place a Kotlin class file in src/main/kotlin that depends on that Groovy class. (i.e., Book)

Additional research notes:

• The solution provided for an earlier Gradle version is no longer working: Gradle 6+ : compile groovy before kotlin (there is an error message about 'classpath' as unknown property for compileKotlin)
• Here is another one that does not work: Compile Groovy and Kotlin?
• And yet another approach that no longer works: Gradle Kotlin Dsl Build for a Kotlin Gradle Plugin, which depends on a Groovy Class in the same Project

Solution

The base idea of the documentation at https://docs.gradle.org/current/userguide/building_java_projects.html#sub:compile_deps_jvm_lang and thus the solution in Gradle 6+ : compile groovy before kotlin you posted stays the same.

You remove the groovy => java dependency and add a kotlin => groovy dependency.

That the linked answer does not literally work has nothing to do with Gradle 6 vs. Gradle 8.

Your problem is Kotlin Gradle Plugin <1.8 vs. >=1.8 as in 1.8 the deprecated classpath property was finally made an error and later removed, in favor of libraries.

So here the version of the configuration that works with your version as Kotlin DSL snippet:

tasks.compileGroovy {
    classpath = sourceSets.main.get().compileClasspath
}

tasks.compileKotlin {
    libraries.from(sourceSets.main.get().groovy.classesDirectory)
}

Answered By - Vampire

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how to enable @Preview for kotlin desktop compose demo project?

Issue

I downloaded the demo project to study kotlin compose.

I try to add @Preview on a @Composable fun, but get warn that: Unresolved reference: Preview

I add implementation("androidx.compose.ui:ui-tooling-preview:1.1.1") in kotlin.sourceSets.named("CommonMain").dependencies in build.gradlw.kts:

        named("commonMain") {
            dependencies {
                api(compose.runtime)
                api(compose.foundation)
                api(compose.material)
                api(compose.materialIconsExtended)
                implementation("androidx.compose.ui:ui-tooling-preview:1.1.1")
            }
        }

But still get Unresolved reference: Preview error.

I use IDEA 2021.3.3, Build #IU-213.7172.25, built on March 16, 2022.

Solution

You need to import androidx.compose.desktop.ui.tooling.preview.Preview to preview in desktop.

Go to Settings > Plugins > search in the marketplace for Compose Multiplatform IDE Support and Install this plugin.

After that, you can use Preview annotation and it will import the correct lib.

Answered By - Roman

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Read mesibo local db using Room Library

Issue

I'm using device explorer and find mesibo local database written using SQLite

It's possible to access that file using Room library rather than using mesibo SDK?, I want to make advance query and use livedata, coroutines etc, to reduce code complexity

Solution

While it is technically possible to access mesibo database directly, this is not the recommended or supported operation for a few reasons:

• Although the mesibo database structure is open, it is meant for mesibo's internal use only and subject to change without notice in future mesibo versions. Any code written to directly access the database would be prone to breaking with mesibo updates.

• Direct database access bypasses the mesibo SDK and cache, as well as the SDK's mechanisms for managing data consistency, synchronization, etc. This could lead to issues like data corruption.

If you have a specific need that the SDK does not address, please email us a feature request. We're happy to look into supporting your use case.

Answered By - mesibo

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notifyDataSetChanged on fragment does not work

Issue

I'm building an app, I have a chat I moved into a fragment. it worked before and now it doesn't. I understand it's a known problem but still I couldn't solve the issue. When I'm debugging I can see that I'm getting the messages from firebase and the list at the adapter is not empty but after notifyDataSetChanged I see that onBindViewHolder or the holders are never being called. I tried from UiThread and from the callback but I still doesn't see the messages

chat fragment xml:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".fragments.saloon.ChatFragment">

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/recyclerview_chat"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:visibility="visible"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />


</FrameLayout>

activity xml:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorPrimary"
    tools:context=".activities.SaloonMobileScreenActivity">

    <com.google.android.material.tabs.TabLayout
        android:id="@+id/tabBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="parent"
        app:tabIndicatorColor="@color/colorSecondary"
        app:tabSelectedTextColor="@color/colorSecondary"
        app:tabTextAppearance="@style/TabLayoutTextFont"
        app:tabTextColor="@color/colorPrimaryLight">

        <!--        android:id="@+id/tabChat"-->
        <com.google.android.material.tabs.TabItem
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/chat" />

        <!--        android:id="@+id/tabUsers"-->
        <com.google.android.material.tabs.TabItem
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/users" />

    </com.google.android.material.tabs.TabLayout>

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="3dp"
        app:layout_behavior="com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior"
        app:layout_constrainedHeight="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tabBar"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintVertical_bias="1.0">

    </androidx.viewpager2.widget.ViewPager2>

</androidx.constraintlayout.widget.ConstraintLayout>

In the Activity I have:

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivitySaloonMobileScreenBinding.inflate(layoutInflater)
        setContentView(binding!!.root)

        setTabs()
        
    }

    private fun setTabs() {
        pagerAdapter = FragmentPagerAdapter(this)
        pagerAdapter.addFragment(ChatFragment(saloonOwnerUid!!, saloonName!!), resources.getString(R.string.chat))
        pagerAdapter.addFragment(UsersFragment(), resources.getString(R.string.users))
        binding!!.viewPager.adapter = pagerAdapter
        binding!!.viewPager.currentItem = 0
        TabLayoutMediator(binding!!.tabBar, binding!!.viewPager) { tab, position ->
            tab.text = pagerAdapter.getTabTitle(position)
        }.attach()
    }

And in the fragment code I tried:

    private val onDataChangeCb : (ArrayList<MessageModel>) -> Unit = { msgList ->
        messages!!.clear()
        messages!!.addAll(msgList)
        (context as SaloonMobileScreenActivity).runOnUiThread {
            msgAdapter!!.updateAdapter(msgList)
        }
        msgAdapter!!.notifyDataSetChanged()
        binding!!.recyclerviewChat.smoothScrollToPosition(msgAdapter!!.itemCount)
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        messages = ArrayList()
        binding = FragmentChatBinding.inflate(layoutInflater)
        BaseBillboActivity.getDbManager().addChatListener(onDataChangeCb, saloonOwnerUid, saloonName)
        msgAdapter = MessagesAdapter(requireActivity(), messages!!, senderUid)
        binding!!.recyclerviewChat.layoutManager = LinearLayoutManager(context)
        binding!!.recyclerviewChat.adapter = msgAdapter
        return inflater.inflate(R.layout.fragment_chat, container, false)
    }

Solution

Issue might be caused by the order of operations in the onCreateView do this instead and return binding.root

override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        messages = ArrayList()
        binding = FragmentChatBinding.inflate(layoutInflater)

    // Set up the RecyclerView after inflating the Layout
      binding!!.recyclerviewChat.layoutManager = LinearLayoutManager(context)
      msgAdapter = MessagesAdapter(requireActivity(), messages!!, senderUid)
      binding!!.recyclerviewChat.adapter = msgAdapter

      BaseBillboActivity.getDbManager().addChatListener(onDataChangeCb, 
      saloonOwnerUid, saloonName)
       return binding.root
}

Answered By - Saloni Tyagi

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is it okay? to have same name of parameter and variable in function call in kotlin

Issue

i have query that is it fine to use to use named parameter which having name parameter and the variable name same in a function call

for example

fun fun1( to:string ){
//body}

fun fun2( ){
to = "xyz"
fun1( to = to)
}

calling fun1 which have a parameter name "to" and passing variable "to" is it okay to do so . In either of case can someone also explain how the compiler will resolve this

Solution

In Kotlin, property or variable assignment can only happen if the variable/property name and = are at the beginning of a line of code (or the first code in the scope { } of a lambda or defined function), not in the middle of an expression or list of function arguments.

Since the compiler sees to = inside the argument list of a function call, it resolves it as a named argument rather than a variable assignment, so the to of to = is interpreted as a function parameter name.

Answered By - Tenfour04

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Memory leak in kotlin due to Closures?

Issue

I have a basic understanding of memory management in Kotlin i.e. local variables are stored in the stack and are managed by the OS and the objects are created on the heap and JVM manages them. Moreover, objects are passed as copy of reference and primitive types are passed as copy in functions.

In the below code, I have created a TextEditOperation function that creates an EditText programmatically and sets its properties using an instruction object and added a TextWatcher to it and at last added the edittext view to parent relative layout.

public fun TextEditOperation (pInstructionSetIndex: Int, pInstructionIndex: Int): View? 
{
    val instruction: InstructionKernelAndroid
    val context: Context?
    val activity: Activity
    val textedit: EditText
    val parent_view: RelativeLayout

    // fetch the instruction
    instruction = InstructionSetMgr.uAndroidOSInstructionSetList[pInstructionSetIndex][pInstructionIndex]

    // get activity's Context
    context = ProcessStates.GetMainActivityContext ()

    // cast activity's context to activity to use it's method
    activity = context as Activity

    // get parent view
    parent_view = activity.findViewById (instruction.GetParentID ()) as RelativeLayout

    // create view
    textedit = EditText (context)

    // set view properties

    textedit.id = instruction.GetElementID ()
    textedit.hint = instruction.GetHintText ()
    textedit.layoutParams = RelativeLayout.LayoutParams (
        instruction.GetWidth (),
        instruction.GetHeight ()
    )
    textedit.x = instruction.GetX ()
    textedit.y = instruction.GetY ()
    textedit.setBackgroundColor (Color.parseColor (instruction.GetBackgroundColor ()))
    textedit.setTextColor (Color.parseColor (instruction.GetTextColor ()))
    
    // create and add a TextWatcher to the EditText

        val text_watcher: TextWatcher

    text_watcher = object : TextWatcher {
    
        override fun beforeTextChanged (s: CharSequence, start: Int, count: Int, after: Int)
        {
            
        }
    
        override fun onTextChanged (s: CharSequence, start: Int, before: Int, count: Int) 
        {
            TextChanged (pInstructionSetIndex + 1, textedit.length (), textedit.id)
        }
    
        override fun afterTextChanged (s: Editable)
        {
            
        }
    } 
    // add the textwatcher
    textedit.addTextChangedListener (text_watcher)
    
    // add view to parent view
    parent_view.addView (textedit);

    return textedit;  
}

Now, what I understand is if the text_watcher object wouldn't have been there, then for line

textedit = EditText (context)

EditText(context) object would have been created on the heap(managed by JVM) and variable textedit (managed by OS) refering the object would have been on stack. So the textedit variable would have been cleared from the stack memory by the OS once the function scope ends.

However, now as I am using the textedit variable inside the OnTextChanged function of the text_watcher:

override fun onTextChanged (s: CharSequence, start: Int, before: Int, count: Int) 
{
     TextChanged (pInstructionSetIndex + 1, textedit.length (), textedit.id)
}

And the onTextChanged function will get called much after the TextEditOperation's function scope has ended still How I'm able to access the length and id of the EditText using textedit variable which should have been removed by the OS by now?

Is it because of closures in kotlin, than I'm able to access the varible that's present in the outer scope and hence it not getting free by the OS thus being a memory leak, if yes how to fix it or is there any other reason behind it?

Solution

Disclaimer: This answer focuses on Kotlin when targeting the JVM. The general concepts should be applicable to other platforms, but the specifics are likely to differ.

---

Closures & Variable Capturing

When a closure makes use of a variable from the enclosing scope, that closure "captures" the value of the variable at the time the closure is created.

In Kotlin, this is implemented by implicitly adding a class property to the class generated for the closure object. The property is initialized with the value of the captured variable during instantiation of the closure. Within the closure's scope, any time it looks like you are using the captured variable you are actually using the property. All this is done for you by the compiler behind the scenes.

So, using textedit inside your TextWatcher implementation is perfectly okay.

• The value of that variable is captured when the TextWatcher is created, not when the variable is first "used" in the implementation.

• All references to textedit within the scope of the TextWatcher implementation are actually referencing a hidden, implicitly defined property of said implementation. Meaning there is no attempt to access a local variable after it has been popped off the stack.

Note that when a closure references a class property of its enclosing class, the closure actually captures the instance of the enclosing class (i.e., this) instead of the value of the property directly. Also, unlike Java, Kotlin is capable of capturing mutable local variables (i.e., var), which it accomplishes by using a hidden "wrapper class" that wraps the actual value, then captures that wrapper object instead.

Conceptual Example

Here is some code demonstrating the concept of what the compiler is doing. This is not necessarily exactly how variable capturing is implemented, but it should hopefully help with understanding the idea.

If you have something like this:

interface Printer {
    fun print()
}

fun createPrinter(): Printer {
    val message = "Hello, World" // local variable
    return object : Printer {
        override fun print() = println(message)
    }
}

After compilation, it would be as if you wrote the following:

interface Printer {
    fun print()
}

fun createPrinter() : Printer {
    val message = "Hello, World" // local variable
    class AnonymousPrinterImpl(
        private val message: String // class property
    ): Printer {
        // Here, 'message' is referring to the class property,
        // not the local variable.
        override fun print() = println(message)
    }
    return AnonymousPrinterImpl(message)
}

If you want to see what the compiler actually generates then you can inspect the Java byte-code via the javap tool. Note that the implementation for an anonymous object is different than for a functional interface or lambda expression, but the end result is the same: A class property is implicitly added to the closure's class.

---

Memory Management

In Kotlin, heap memory is managed by a garbage collector. At a high level, the way a garbage collector works is by periodically traversing the current object graph, starting at designated root objects. Any object that cannot be reached from those root objects is eligible for garbage collection. In languages with a garbage collector, a "memory leak" occurs when an object remains strongly referenced after the program no longer needs it. The strong reference prevents the unneeded object from being collected by the garbage collector.

You seem to be worried the TextWatcher is erroneously keeping the TextEdit object in memory after your function returns. But you are returning the TextEdit object from the function and adding it to some "parent view". Both those things strongly indicate the TextEdit object is still needed by your program after the function returns.

Additionally, the only strong reference to the TextWatcher after your function returns is by the TextEdit. In this case, it is not the TextWatcher keeping the TextEdit in memory, but rather the other way around. When the TextEdit becomes eligible for garbage collection, so will the TextWatcher. The circular reference between the two does not change that. 

In short, there is no memory leak in your code; or at least not one caused by the TextWatcher based on what you have shown us.

Answered By - Slaw

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Kotlin Ternary Conditional Operator

Issue

What is the equivalent of this expression in Kotlin?

a ? b : c

This is not valid code in Kotlin.

Solution

In Kotlin, if statements are expressions. So the following code is equivalent:

if (a) b else c

The distinction between expression and statement is important here. In Java/C#/JavaScript, if forms a statement, meaning that it does not resolve to a value. More concretely, you can't assign it to a variable.

// Valid Kotlin, but invalid Java/C#/JavaScript
var v = if (a) b else c

If you're coming from a language where if is a statement, this might seem unnatural but that feeling should soon subside.

Answered By - Drew Noakes

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Using Eclipse for Kotlin programming does not work correctly

Issue

as a Java programmer, I have recently decided to learn Kotlin and have encountered a problem with Eclipse and Kotlin. Both Eclipse and the plugins were all updated to the latest version.

Here's the situation in Eclipse.

Code that works totally fine:

fun main(args: Array<String>) {
  
  println("Starting program...")
  var a = 10
  var b = 5
  
  println("Variables \"a\" and \"b\" initialized, printing variables:")
  println(a)
  println(b)
  println("Program ended.")
}

Output: Starting program... Variables initialized, printing variables: 10 5 Program ended.

Code that does not work at all, note that I changed the values of a and b (important):

fun main(args: Array<String>) {

  println("Starting program...")
  var a = 20
  var b = 10

  println("Variables \"a\" and \"b\" initialized, adding both together...")
  
  //adding a and b together
  var c = a+b  //**Error occurs for a fraction of a second**: ERROR: Cannot access 'java.io.Serializable' which is a supertype of 'kotlin.Int'. Check your module classpath for missing or conflicting dependencies

  println("Printing sum of \"a\" and \"b\": ")
  println(c)
  println("Program ended.")
  
}

Output: Same output as from the last successful run

I needed to record what Eclipse was doing, just so that I can read the error message when the footage was paused.

After that, I checked the classpath (as the error message suggested) and no dependencies were missing.

Here's one rather strange observation that I made. Restarting Eclipse and running the same "erroneous" code results in the output from the last successful run (before restarting Eclipse), in this case it was Starting program... Variables initialized, printing variables: 10 5 Program ended.

What I tried

1. searched StackOverFlow for an existing/similar topic
2. checked if the latest Kotlin compiler was installed (it is)
3. compiled the "erroneous" .kt file manually via command prompt (it worked fine, so I guess it's a problem with Eclipse)
4. configured the build path and moved the Kotlin libraries from class path to module path, which resulted in Eclipse not being able to run the program at all (ClassNotFoundException)
5. deleted the Kotlin library from the build path completely, this resulted in working code, but only without basic arithmetic operations with the integer values
6. restarted Eclipse again and noticed that the Kotlin libraries were back in the class path, without changing it myself
7. deliberately tried to switch perspectives to Java and back to Kotlin, error persists
8. tried to run the program in vs code, it worked there...
9. reinstalled Eclipse and the Kotlin plugins, didn't work

What's my question(s)

Does someone know what causes this strange behaviour or has experienced something similar? And if so, is there something that I could try which worked for you, or is there something that I haved missed out on?

Thank you for reading

Thank you very much for reading!

Solution

Digging deeper into the matter here, I finally found a solution that is over 3 years old, but still works out: cannot access 'java.io.Serializable'

Answered By - Frontalschaden

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