Android Kotlin Progress Bar become unresolved reference

Issue

I am new at using Kotlin in Android Studio and I tried to learn on how to use the progress bar by following a simple tutorial on youtube. However, for some reason the "progressBar" on progressBar.max in MainActivity.kt is defined as unresolved reference although my code is identical with the guy in the video.

This is activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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=".MainActivity">

    <ProgressBar
        android:id="@+id/progressBar"
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_width="335dp"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:scaleY="10" />

</RelativeLayout>

This is MainActivity.kt

package com.example.game1

import android.animation.ObjectAnimator
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

       progressBar.max=10

        val currentProgress = 6

        ObjectAnimator.ofInt(progressBar, propertyName: "progress", currentProgress)
        .setDuration(2000)
            .start()
    }
}

Solution

Seems like you've watched a tutorial where somebody used Kotlin synthetics to access Views from the code. They are deprecated now and I suggest you use either Muhammad Ahmed solution or View Binding

In module's build.gradle locate this piece of code:

android {
    compileSdk 31
    ...
}

Now add the view binding build feature, it should look like this:

android {
    compileSdk 31

    buildFeatures {
        viewBinding = true
    }
   
   ...

}

After you make the changes, a blue bar at the top should appear. Sync your project and now it supports view binding.

Your MainActivity.kt should look like this:

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding  // name of your layout in camelcase

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

        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        binding.progressBar.max = 10
    }
}

How do you access Views with the view binding? Use camelcase. For example, if you have TextView with id "tv_list_description" it can be accessed in the code like this:

binding.tvListDescription.text = "Sample text"

Answered By - Corec