Android KTX Part of Android Jetpack.
Android KTX is a set of Kotlin extensions that are included with Android Jetpack and other Android libraries. KTX extensions provide concise, idiomatic Kotlin to Jetpack, Android platform, and other APIs. To do so, these extensions leverage several Kotlin language features, including the following:
- Extension functions
- Extension properties
- Lambdas
- Named parameters
- Parameter default values
- Coroutines
As an example, when working with
SharedPreferences
, you must
create an editor
before you can make modifications to the preferences data. You must also apply
or commit those changes when you are finished editing, as shown in the following
example:
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 a
more concise approach by passing a block of code to execute after the editor is
created, letting the code execute, and then letting the SharedPreferences
API
apply 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 an
optional boolean
flag as its first argument that indicates whether to commit
or apply the changes. It also receives an action to perform on the
SharedPreferences
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 asynchronously
sharedPreferences.edit { putBoolean("key", value) }
// Commit a new value synchronously
sharedPreferences.edit(commit = true) { putBoolean("key", value) }
The caller can choose whether to commit or apply the changes. The action
lambda is itself an anonymous extension function on SharedPreferences.Editor
which 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 (or
inline) the compiled bytecode for the function each time the function is used.
This avoids the overhead of instantiating a new class for every action
each
time this function is called.
This pattern of passing code using lambdas, applying sensible defaults that can
be overridden, and adding these behaviors to existing APIs using inline
extension functions is typical of the enhancements provided by the Android KTX
library.
Use Android KTX in your project
To start using Android KTX, add the following dependency to your project's
build.gradle
file:
Groovy
repositories { google() }
Kotlin
repositories { google() }
AndroidX Modules
Android KTX is organized into modules, where each module contains one or more packages.
You must include a dependency for each module artifact in your app's
build.gradle
file. Remember to append the version number to the artifact.
You can find the latest version numbers in each artifact's corresponding section
in this topic.
Android KTX contains a single core module that provides Kotlin extensions for common framework APIs and several domain-specific extensions.
With the exception of the core module, all KTX module artifacts replace the
underlying Java dependency in your build.gradle
file. For example, you can
replace a androidx.fragment:fragment
dependency with
androidx.fragment:fragment-ktx
. This syntax helps to better manage
versioning and does not add additional dependency declaration requirements.
Core KTX
The Core KTX module provides extensions for common libraries that are part of
the Android framework. These libraries do not have Java-based dependencies that
you need to add to build.gradle
.
To include this module, add the following to your app's build.gradle
file:
Groovy
dependencies { implementation "androidx.core:core-ktx:1.13.1" }
Kotlin
dependencies { implementation("androidx.core:core-ktx:1.13.1") }
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's
memory-efficient collection libraries, including ArrayMap
, LongSparseArray
,
LruCache
, and others.
To use this module, add the following to your app's build.gradle
file:
Groovy
dependencies { implementation "androidx.collection:collection-ktx:1.4.4" }
Kotlin
dependencies { implementation("androidx.collection:collection-ktx:1.4.4") }
Collection extensions take advantage of Kotlin’s operator overloading to simplify things like collection concatenation, as shown in the following example:
// 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
The Fragment KTX module provides a number of extensions to simplify the fragment API.
To include this module, add the following to your app's build.gradle
file:
Groovy
dependencies { implementation "androidx.fragment:fragment-ktx:1.8.4" }
Kotlin
dependencies { implementation("androidx.fragment:fragment-ktx:1.8.4") }
With the Fragment KTX module, you can simplify fragment transactions with lambdas, 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
and
activityViewModels
property delegates:
// Get a reference to the ViewModel scoped to this Fragment
val viewModel by viewModels<MyViewModel>()
// Get a reference to the ViewModel scoped to its Activity
val viewModel by activityViewModels<MyViewModel>()
Lifecycle KTX
Lifecycle KTX defines a LifecycleScope
for each
Lifecycle
object. Any coroutine
launched in this scope is canceled when the Lifecycle
is destroyed. You can
access the CoroutineScope
of the Lifecycle
by using the
lifecycle.coroutineScope
or lifecycleOwner.lifecycleScope
properties.
To include this module, add the following to your app's build.gradle
file:
Groovy
dependencies { implementation "androidx.lifecycle:lifecycle-runtime-ktx:2.8.6" }
Kotlin
dependencies { implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.8.6") }
The following example demonstrates how to use lifecycleOwner.lifecycleScope
to
create 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. For
example, you might want to retrieve a user's preferences and serve them to your
UI. For these cases, LiveData KTX provides a liveData
builder function that
calls 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:
Groovy
dependencies { implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.8.6" }
Kotlin
dependencies { implementation("androidx.lifecycle:lifecycle-livedata-ktx:2.8.6") }
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
, see
Use Kotlin coroutines with Architecture components.
Navigation KTX
Each component of the Navigation library has its own KTX version that adapts the API to be more succinct and Kotlin-idiomatic.
To include these modules, add the following to your app's build.gradle
file:
Groovy
dependencies { implementation "androidx.navigation:navigation-runtime-ktx:2.8.2" implementation "androidx.navigation:navigation-fragment-ktx:2.8.2" implementation "androidx.navigation:navigation-ui-ktx:2.8.2" }
Kotlin
dependencies { implementation("androidx.navigation:navigation-runtime-ktx:2.8.2") implementation("androidx.navigation:navigation-fragment-ktx:2.8.2") implementation("androidx.navigation:navigation-ui-ktx:2.8.2") }
Use the extension functions and property delegation to access destination arguments 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
The Palette KTX module offers idiomatic Kotlin support for working with color palettes.
To use this module, add the following to your app's build.gradle
file:
Groovy
dependencies { implementation "androidx.palette:palette-ktx:1.0.0" }
Kotlin
dependencies { implementation("androidx.palette:palette-ktx:1.0.0") }
As an example, when working with a Palette
instance, you can retrieve the
selected
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 from
a ReactiveStreams
publisher.
To include this module, add the following to your app's build.gradle
file:
Groovy
dependencies { implementation "androidx.lifecycle:lifecycle-reactivestreams-ktx:2.8.6" }
Kotlin
dependencies { implementation("androidx.lifecycle:lifecycle-reactivestreams-ktx:2.8.6") }
As an example, assume a database with a small list of users. In your app, you
load the database into memory and then display user data in your UI. To achieve
this, you might use RxJava.
The Room
Jetpack component can retrieve
the user list as a Flowable
. In this scenario, you must also manage the Rx
publisher subscription across the life of your fragment or activity.
With LiveDataReactiveStreams
, however, you can benefit from RxJava and its
rich set of operators and work-scheduling capabilities while also working with
the 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:
Groovy
dependencies { implementation "androidx.room:room-ktx:2.6.1" }
Kotlin
dependencies { implementation("androidx.room:room-ktx:2.6.1") }
Here are a couple of examples where Room now uses coroutines. The first example
uses a suspend
function to return a list of User
objects, while the second
utilizes Kotlin's Flow
to asynchronously return the User
list. Note that when using Flow
, you're
also 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 of boilerplate code.
To use this module, add the following to your app's build.gradle
file:
Groovy
dependencies { implementation "androidx.sqlite:sqlite-ktx:2.4.0" }
Kotlin
dependencies { implementation("androidx.sqlite:sqlite-ktx:2.4.0") }
Here's an example of using the transaction
extension to perform a database
transaction:
db.transaction {
// insert data
}
ViewModel KTX
The ViewModel KTX library provides a viewModelScope()
function that makes it
easier to launch coroutines from your ViewModel
. The
CoroutineScope
is bound to Dispatchers.Main
and is automatically cancelled
when the ViewModel
is cleared. You can use viewModelScope()
instead of
creating a new scope for each ViewModel
.
To include this module, add the following to your app's build.gradle
file:
Groovy
dependencies { implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.8.6" }
Kotlin
dependencies { implementation("androidx.lifecycle:lifecycle-viewmodel-ktx:2.8.6") }
As an example, the following viewModelScope()
function launches a coroutine
that makes a network request in a background thread. The library handles all of
the 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:
Groovy
dependencies { implementation "androidx.work:work-runtime-ktx:2.9.1" }
Kotlin
dependencies { implementation("androidx.work:work-runtime-ktx:2.9.1") }
Instead of extending Worker
, you can now
extend CoroutineWorker
,
which has a slightly different API. For example, if you wanted to build a simple
CoroutineWorker
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
, see
Threading in CoroutineWorker.
WorkManager KTX also adds extension functions to Operations
and
ListenableFutures
to suspend the current coroutine.
Here's an example that suspends the
Operation
that's returned by
enqueue()
:
// 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 that enable you to write idiomatic Kotlin code when using Firebase in your app. For more information, see the following topics:
Google Maps Platform KTX
There are KTX extensions available for Google Maps Platform Android SDKs which allow you to take advantage of several Kotlin language features such as extension functions, named parameters and default arguments, destructuring declarations, and coroutines. For more information, see the following topics:
Play Core KTX
Play Core KTX adds support for Kotlin coroutines for one-shot requests and Flow
for monitoring status updates by adding extension functions to
SplitInstallManager
and AppUpdateManager
in the Play Core library.
To include this module, add the following to your app's build.gradle
file:
Groovy
dependencies { implementation "com.google.android.play:core-ktx:1.8.1" }
Kotlin
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 the Android KTX issue tracker.