after upgrading, my project could not find resource file R but still running app showing no error. how to solve

Issue

I am facing a peculiar problem. i have upgraded my project from 23 api to 28. after upgrading, from my activity there showing cannot resolve R but while i run its building apk successfully and app running well without any showing any error. 2 more UI name also not recognizing in "setContentView" i have check that UIs no problem there. how to check for more specifically for UI error if exist.

apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    buildToolsVersion "28.0.3"
    defaultConfig {

        minSdkVersion 18
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        multiDexEnabled true
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    configurations.all {
        resolutionStrategy.force 'com.google.code.findbugs:jsr305:3.0.1'
    }
    configurations {
        compile.exclude group: "org.apache.httpcomponents", module: "httpclient"
        all*.exclude group: 'xpp3', module: 'xpp3'
    }
    packagingOptions {
        exclude 'META-INF/LICENSE'
        exclude 'META-INF/LICENSE-FIREBASE.txt'
        exclude 'META-INF/NOTICE'
    }
    repositories {
        jcenter()
        maven { url "https://dl.bintray.com/hani-momanii/maven" }
    }

    aaptOptions {
        cruncherEnabled = false
    }

    lintOptions {
        checkReleaseBuilds false
        //If you want to continue even if errors found use following line
        abortOnError false
    }

}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    androidTestImplementation('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })


    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support:design:28.0.0'
    implementation 'com.google.android.gms:play-services-auth:16.0.0'
    implementation 'com.github.delight-im:Android-AdvancedWebView:v3.0.0'
    implementation 'com.google.gdata:core:1.47.1'
    implementation 'com.android.support:support-v4:28.0.0'
    implementation 'com.android.support:support-v13:28.0.0'
    implementation 'com.android.support:recyclerview-v7:28.0.0'
    implementation 'com.google.android.gms:play-services-nearby:16.0.0'
    implementation 'com.google.android.gms:play-services-location:16.0.0'
    implementation 'com.google.android.gms:play-services-places:16.0.0'
    implementation 'com.google.android.gms:play-services-maps:16.0.0'
    implementation 'com.squareup.picasso:picasso:2.5.2'
    implementation 'com.google.code.gson:gson:2.8.5'
    implementation 'com.github.markomilos:paginate:0.5.1'
    implementation 'com.github.lovetuzitong:MultiImageSelector:1.2'
    implementation 'com.github.bumptech.glide:glide:4.9.0'
    implementation 'com.iarcuschin:simpleratingbar:0.1.5'
    implementation 'com.droidninja:filepicker:2.1.1'
    implementation 'com.google.android:flexbox:1.0.0'
    implementation 'com.felipecsl.asymmetricgridview:library:2.0.1'

    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'

}
apply plugin: 'com.google.gms.google-services'

build.gradle:

buildscript {
    repositories {
        jcenter()
        maven {
            url 'https://maven.google.com/'
            name 'Google'
        }
        google()

    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.3.2'
        classpath 'com.google.gms:google-services:4.2.0'

    }
}

allprojects {
    repositories {
        jcenter()
        mavenCentral()
        maven { url "https://jitpack.io" }
        maven {
            url 'https://maven.google.com/'
            name 'Google'
        }
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

can anyone please help me.

Solution

There are a few reasons for this problem and also a few solutions:

First thing to try is to Invalidate caches and restart, usually it's just an Android Studio caching problem

If that doesn't work you might have a Gradle/Android Studio version problem. Usually when you upgrade your compile SDK, also the gradle version needs to be updated, but Android Studio complains with the error you are getting (already happened to me). Also update your Android Studio to the latest stable version (my guess goes to this solution to your problem)

Answered By - Ricardo