Android KTX  |  Kotlin  |  Android Developers (2024)

Android KTX is a set of Kotlin extensions that are included with AndroidJetpack and other Android libraries. KTX extensions provide concise,idiomatic Kotlin to Jetpack, Android platform, and other APIs. To do so, theseextensions leverage several Kotlin language features, including the following:

• Extension functions
• Extension properties
• Lambdas
• Named parameters
• Parameter default values
• Coroutines

As an example, when working withSharedPreferences, you mustcreate an editorbefore you can make modifications to the preferences data. You must also applyor commit those changes when you are finished editing, as shown in the followingexample:

sharedPreferences .edit() // create an Editor .putBoolean("key", value) .apply() // write to disk asynchronously

Kotlin lambdas are a perfect fit for this use case. They allow you to take amore concise approach by passing a block of code to execute after the editor iscreated, letting the code execute, and then letting the SharedPreferences APIapply the changes atomically.

Here's an example of one of the Android KTX Core functions,SharedPreferences.edit,which adds an edit function to SharedPreferences. This function takes anoptional boolean flag as its first argument that indicates whether to commitor apply the changes. It also receives an action to perform on theSharedPreferences editor in the form of a lambda.

// SharedPreferences.edit extension function signature from Android KTX - Core// inline fun SharedPreferences.edit(// commit: Boolean = false,// action: SharedPreferences.Editor.() -> Unit)// Commit a new value asynchronouslysharedPreferences.edit { putBoolean("key", value) }// Commit a new value synchronouslysharedPreferences.edit(commit = true) { putBoolean("key", value) }

The caller can choose whether to commit or apply the changes. The actionlambda is itself an anonymous extension function on SharedPreferences.Editorwhich returns Unit, as indicated by its signature. This is why inside the block, you are able to perform the work directly on the SharedPreferences.Editor.

Finally, the SharedPreferences.edit() signature contains the inline keyword.This keyword tells the Kotlin compiler that it should copy and paste (orinline) the compiled bytecode for the function each time the function is used.This avoids the overhead of instantiating a new class for every action eachtime this function is called.

This pattern of passing code using lambdas, applying sensible defaults that canbe overridden, and adding these behaviors to existing APIs using inlineextension functions is typical of the enhancements provided by the Android KTXlibrary.

Use Android KTX in your project

To start using Android KTX, add the following dependency to your project'sbuild.gradle file:

repositories { google()}

repositories { google()}

AndroidX Modules

Android KTX is organized into modules, where each module contains one or morepackages.

You must include a dependency for each module artifact in your app'sbuild.gradle file. Remember to append the version number to the artifact.You can find the latest version numbers in each artifact's corresponding sectionin this topic.

Android KTX contains a single core module that provides Kotlinextensions for common framework APIs and several domain-specific extensions.

With the exception of the core module, all KTX module artifacts replace theunderlying Java dependency in your build.gradle file. For example, you canreplace a androidx.fragment:fragment dependency withandroidx.fragment:fragment-ktx. This syntax helps to better manageversioning and does not add additional dependency declaration requirements.

Core KTX

The Core KTX module provides extensions for common libraries that are part ofthe Android framework. These libraries do not have Java-based dependencies thatyou need to add to build.gradle.

To include this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.core:core-ktx:1.12.0"}

dependencies { implementation("androidx.core:core-ktx:1.12.0")}

Here's a list of the packages that are contained in the Core KTX module:

• androidx.core.animation
• androidx.core.content
• androidx.core.content.res
• androidx.core.database
• androidx.core.database.sqlite
• androidx.core.graphics
• androidx.core.graphics.drawable
• androidx.core.location
• androidx.core.net
• androidx.core.os
• androidx.core.text
• androidx.core.transition
• androidx.core.util
• androidx.core.view
• androidx.core.widget

Collection KTX

The Collection extensions contain utility functions for working with Android'smemory-efficient collection libraries, including ArrayMap, LongSparseArray,LruCache, and others.

To use this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.collection:collection-ktx:1.4.0"}

dependencies { implementation("androidx.collection:collection-ktx:1.4.0")}

Collection extensions take advantage of Kotlin’s operator overloading tosimplify things like collection concatenation, as shown in the followingexample:

// Combine 2 ArraySets into 1.val combinedArraySet = arraySetOf(1, 2, 3) + arraySetOf(4, 5, 6)// Combine with numbers to create a new sets.val newArraySet = combinedArraySet + 7 + 8

Fragment KTX

TheFragment KTX moduleprovides a number of extensions to simplify the fragment API.

To include this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.fragment:fragment-ktx:1.6.2"}

dependencies { implementation("androidx.fragment:fragment-ktx:1.6.2")}

With the Fragment KTX module, you can simplify fragment transactions withlambdas, for example:

fragmentManager().commit { addToBackStack("...") setCustomAnimations( R.anim.enter_anim, R.anim.exit_anim) add(fragment, "...")}

You can also bind to a ViewModel in one line by using the viewModels andactivityViewModels property delegates:

// Get a reference to the ViewModel scoped to this Fragmentval viewModel by viewModels<MyViewModel>()// Get a reference to the ViewModel scoped to its Activityval viewModel by activityViewModels<MyViewModel>()

Lifecycle KTX

Lifecycle KTX defines a LifecycleScope for eachLifecycle object. Any coroutinelaunched in this scope is canceled when the Lifecycle is destroyed. You canaccess the CoroutineScope of the Lifecycle by using thelifecycle.coroutineScope or lifecycleOwner.lifecycleScope properties.

To include this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.lifecycle:lifecycle-runtime-ktx:2.7.0"}

dependencies { implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.7.0")}

The following example demonstrates how to use lifecycleOwner.lifecycleScope tocreate precomputed text asynchronously:

class MyFragment: Fragment() { override fun onViewCreated(view: View, savedInstanceState: Bundle?) { super.onViewCreated(view, savedInstanceState) viewLifecycleOwner.lifecycleScope.launch { val params = TextViewCompat.getTextMetricsParams(textView) val precomputedText = withContext(Dispatchers.Default) { PrecomputedTextCompat.create(longTextContent, params) } TextViewCompat.setPrecomputedText(textView, precomputedText) } }}

LiveData KTX

When using LiveData, you might need to calculate values asynchronously. Forexample, you might want to retrieve a user's preferences and serve them to yourUI. For these cases, LiveData KTX provides a liveData builder function thatcalls a suspend function and serves the result as a LiveData object.

To include this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.7.0"}

dependencies { implementation("androidx.lifecycle:lifecycle-livedata-ktx:2.7.0")}

In the following example, loadUser() is a suspend function declared elsewhere.You can use the liveData builder function to call loadUser() asynchronously,and then use emit() to emit the result:

val user: LiveData<User> = liveData { val data = database.loadUser() // loadUser is a suspend function. emit(data)}

For more information on using coroutines with LiveData, seeUse Kotlin coroutines with Architecture components.

Navigation KTX

Each component of the Navigation library has its own KTX version that adapts theAPI to be more succinct and Kotlin-idiomatic.

To include these modules, add the following to your app's build.gradle file:

dependencies { implementation "androidx.navigation:navigation-runtime-ktx:2.7.7" implementation "androidx.navigation:navigation-fragment-ktx:2.7.7" implementation "androidx.navigation:navigation-ui-ktx:2.7.7"}

dependencies { implementation("androidx.navigation:navigation-runtime-ktx:2.7.7") implementation("androidx.navigation:navigation-fragment-ktx:2.7.7") implementation("androidx.navigation:navigation-ui-ktx:2.7.7")}

Use the extension functions and property delegation to access destinationarguments and navigate to destinations, as shown in the following example:

class MyDestination : Fragment() { // Type-safe arguments are accessed from the bundle. val args by navArgs<MyDestinationArgs>() ... override fun onViewCreated(view: View, savedInstanceState: Bundle?) { view.findViewById<Button>(R.id.next) .setOnClickListener { // Fragment extension added to retrieve a NavController from // any destination. findNavController().navigate(R.id.action_to_next_destination) } } ...}

Palette KTX

ThePalette KTX moduleoffers idiomatic Kotlin support for working with color palettes.

To use this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.palette:palette-ktx:1.0.0"}

dependencies { implementation("androidx.palette:palette-ktx:1.0.0")}

As an example, when working with a Palette instance, you can retrieve theselected swatch for a given target by using the get operator ([ ]):

val palette = Palette.from(bitmap).generate()val swatch = palette[target]

Reactive Streams KTX

Reactive Streams KTX module lets you create an observable LiveData stream froma ReactiveStreams publisher.

To include this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.lifecycle:lifecycle-reactivestreams-ktx:2.7.0"}

dependencies { implementation("androidx.lifecycle:lifecycle-reactivestreams-ktx:2.7.0")}

As an example, assume a database with a small list of users. In your app, youload the database into memory and then display user data in your UI. To achievethis, you might use RxJava.The Room Jetpack component can retrievethe user list as a Flowable. In this scenario, you must also manage the Rxpublisher subscription across the life of your fragment or activity.

With LiveDataReactiveStreams, however, you can benefit from RxJava and itsrich set of operators and work-scheduling capabilities while also working withthe simplicity of LiveData, as shown in the following example:

val fun getUsersLiveData() : LiveData<List<User>> { val users: Flowable<List<User>> = dao.findUsers() return LiveDataReactiveStreams.fromPublisher(users)}

Room KTX

Room extensions add coroutines support for database transactions.

To use this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.room:room-ktx:2.6.1"}

dependencies { implementation("androidx.room:room-ktx:2.6.1")}

Here are a couple of examples where Room now uses coroutines. The first exampleuses a suspend function to return a list of User objects, while the secondutilizes Kotlin's Flowto asynchronously return the User list. Note that when using Flow, you'realso notified of any changes in the tables you're querying.

@Query("SELECT * FROM Users")suspend fun getUsers(): List<User>@Query("SELECT * FROM Users")fun getUsers(): Flow<List<User>>

SQLite KTX

SQLite extensions wrap SQL-related code in transactions, eliminating a lot ofboilerplate code.

To use this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.sqlite:sqlite-ktx:2.4.0"}

dependencies { implementation("androidx.sqlite:sqlite-ktx:2.4.0")}

Here's an example of using the transaction extension to perform a databasetransaction:

db.transaction { // insert data}

ViewModel KTX

The ViewModel KTX library provides a viewModelScope() function that makes iteasier to launch coroutines from your ViewModel. TheCoroutineScope is bound to Dispatchers.Main and is automatically cancelledwhen the ViewModel is cleared. You can use viewModelScope() instead ofcreating a new scope for each ViewModel.

To include this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.7.0"}

dependencies { implementation("androidx.lifecycle:lifecycle-viewmodel-ktx:2.7.0")}

As an example, the following viewModelScope() function launches a coroutinethat makes a network request in a background thread. The library handles all ofthe setup and corresponding scope clearing:

class MainViewModel : ViewModel() { // Make a network request without blocking the UI thread private fun makeNetworkRequest() { // launch a coroutine in viewModelScope viewModelScope.launch { remoteApi.slowFetch() ... } } // No need to override onCleared()}

WorkManager KTX

WorkManager KTX provides first-class support for coroutines.

To include this module, add the following to your app's build.gradle file:

dependencies { implementation "androidx.work:work-runtime-ktx:2.9.0"}

dependencies { implementation("androidx.work:work-runtime-ktx:2.9.0")}

Instead of extending Worker, you can nowextend CoroutineWorker,which has a slightly different API. For example, if you wanted to build a simpleCoroutineWorker to perform some network operations, you can do the following:

class CoroutineDownloadWorker(context: Context, params: WorkerParameters) : CoroutineWorker(context, params) { override suspend fun doWork(): Result = coroutineScope { val jobs = (0 until 100).map { async { downloadSynchronously("https://www.google.com") } } // awaitAll will throw an exception if a download fails, which // CoroutineWorker will treat as a failure jobs.awaitAll() Result.success() }}

For more information on using CoroutineWorker, seeThreading in CoroutineWorker.

WorkManager KTX also adds extension functions to Operations andListenableFutures to suspend the current coroutine.

Here's an example that suspends theOperation that's returned byenqueue():

// Inside of a coroutine...// Run async operation and suspend until completed.WorkManager.getInstance() .beginWith(longWorkRequest) .enqueue().await()// Resume after work completes...

Other KTX modules

You can also include additional KTX modules that exist outside of AndroidX.

Firebase KTX

Some of the Firebase SDKs for Android have Kotlin extension libraries thatenable you to write idiomatic Kotlin code when using Firebase in your app. Formore information, see the following topics:

• Firebase Android SDK
• Firebase Common Kotlin Extensions

Google Maps Platform KTX

There are KTX extensions available for Google Maps Platform Android SDKs whichallow you to take advantage of several Kotlin language features such as extensionfunctions, named parameters and default arguments, destructuring declarations,and coroutines. For more information, see the following topics:

• Maps Android KTX
• Places Android KTX

Play Core KTX

Play Core KTX adds support for Kotlin coroutines for one-shot requests and Flowfor monitoring status updates by adding extension functions toSplitInstallManager and AppUpdateManager in the Play Core library.

To include this module, add the following to your app's build.gradle file:

dependencies { implementation "com.google.android.play:core-ktx:1.8.1"}

dependencies { implementation("com.google.android.play:core-ktx:1.8.1")}

Here's an example of a status-monitoring Flow:

// Inside of a coroutine...// Request in-app update status updates.manager.requestUpdateFlow().collect { updateResult -> when (updateResult) { is AppUpdateResult.Available -> TODO() is AppUpdateResult.InProgress -> TODO() is AppUpdateResult.Downloaded -> TODO() AppUpdateResult.NotAvailable -> TODO() }}

More information

To learn more about Android KTX, see the DevBytes video.

To report an issue or suggest a feature, use theAndroid KTX issue tracker.