Synthetic of kotlin extensions does not work when I import Android-ktx in gradle

Question

I'm trying to test some android jetpack features in my project, I already have the navigation working. When I tried to import android-ktx and migrate my dependencies to androidx I managed to synchronize the gradle successfully, but I lost access to my button through synthetic.

Anyone have any idea what it can be?

My Gradle:

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.qmakercorp.qmaker"
        minSdkVersion 22
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.support.test.runner.AndroidJUnitRunner"
    }

    androidExtensions {
        experimental = true
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.2.71"
    implementation 'androidx.appcompat:appcompat:1.0.0'
    implementation 'com.google.android.material:material:1.0.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'

//    implementation 'com.android.support:appcompat-v7:28.0.0'
//    implementation 'com.android.support:design:28.0.0'
//    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
//    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
//    implementation 'com.android.support:support-v4:28.0.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.1.0-beta01'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.0-beta01'

    implementation "android.arch.navigation:navigation-fragment-ktx:1.0.0-alpha06"
    implementation "android.arch.navigation:navigation-ui-ktx:1.0.0-alpha06"
    androidTestImplementation 'androidx.test:rules:1.1.0-beta01' 

    implementation 'androidx.core:core-ktx:1.0.0'

My Fragment:

Answer 1

In your app build.gradle file you imported androidx.legacy:legacy-support-v4:1.0.0 and clicked Sync Now . After that you had error saying Manifest merger failed : Attribute bla bla ... and commented com.android.support:support-v4:28.0.0 but there wasn't shown Sync Now and you didn't sync your project with gradle files. That's way you still able to use android.support.v4.app.Fragment from LoginFragment . Suggestion: click Sync Project with Gradle Files button and replace import android.support.v4.app.Fragment with import androidx.fragment.app.Fragment .