I did not Import the Recycler View AndroidX Library, yet, I am using it. Why and How is it working?

Question

build.gradle(app)

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.example.todolistapp"
        minSdkVersion 16
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    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:$kotlin_version"

    implementation 'androidx.appcompat:appcompat:1.0.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'

    // Room
    def room_version = "2.0.0"
    implementation "androidx.room:room-runtime:$room_version"
    kapt "androidx.room:room-compiler:$room_version"

    // ViewModel and LiveData
    def lifecycle_version = "2.0.0"
    implementation "androidx.lifecycle:lifecycle-extensions:$lifecycle_version"
    kapt "androidx.lifecycle:lifecycle-compiler:$lifecycle_version"

    // For Floating Action Button
    implementation 'com.google.android.material:material:1.0.0'
}

as you can see from my dependencies, I did not import the recycled view Androidx library.

androidx.recyclerview:recyclerview:1.0.0

but as shown below, I can comfortably use it in my layout (activity_main.xml) and MainActivity code.

<?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"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerViewTasks"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clipToPadding="false"
        android:paddingBottom="80dp"/>

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="16dp"
        android:tint="@android:color/white"
        app:srcCompat="@android:drawable/ic_input_add"/>
</FrameLayout>

MainActivity.kt

import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity(), TaskAdapter.TaskViewCliskListener {

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

        recyclerViewTasks.layoutManager = LinearLayoutManager(this)
}

What is responsible for this behavior?

Answer 1

As per the dependencies of the com.google.android.material:material:1.0.0:

androidx.recyclerview:recyclerview:1.0.0

This means that the Material library takes a transitive dependency on RecyclerView already and you don't need to manually include it yourself.