"An Anvil forges a Dagger. A Whetstone sharpens it. And when you're not planning on using your Dagger, you may keep it in something that rhymes with kilt." — Tiago Cunha.
Whetstone provides a simplified way to incorporate Dagger and Anvil into an Android application.
The goals of Whetstone are:
- To simplify Dagger-related infrastructure for Android apps.
- To create a standard set of components and scopes to ease setup, but allowing customizations.
- All generated code is in Kotlin, which can have significant benefits in a Kotlin only codebase
- Whetstone avoids KAPT completely for performance reasons by taking advantage of Anvil compiler.
- Whetstone is extensible by using the powers of Dagger and Anvil.
- Whetstone significantly reduces boiler plate.
- Whetstone doesn't do bytecode manipulation for complementing classes. Hilt does.
- Summarily, while philosophies are similar, whetstone is relatively easier to work with ;).
First you must apply whetstone plugin in the build.gradle file of any module that requires dependency injection:
plugins {
id("com.deliveryhero.whetstone").version("<latest version>")
}Or you can use the old way to apply a plugin:
// In root build.gradle.kts
buildscript {
repositories {
mavenCentral()
}
dependencies {
classpath("com.deliveryhero.whetstone:whetstone-gradle-plugin:${latest_version}")
}
}
// In individual modules
apply(plugin = "com.deliveryhero.whetstone")This automatically configures Dagger and Anvil, and also adds the necessary whetstone dependencies for you.
To use whetstone, you must initialize it in your Application class.
@ContributesAppInjector(generateAppComponent = true)
class MyApplication : Application(), ApplicationComponentOwner {
override val applicationComponent by lazy {
GeneratedApplicationComponent.create(this)
}
}Note: For more sophisticated use cases, the generated app component might not be sufficient for you. In such scenario, you can disable automatic generation of app component, and create your own instead. An example may look like this:
@Singleton // Optional. Can be omitted if you never use this annotation
@SingleIn(ApplicationScope::class)
@MergeComponent(ApplicationScope::class)
interface MyApplicationComponent : ApplicationComponent {
@Component.Factory
interface Factory {
fun create(
@BindsInstance application: Application, // this is necessary for whetstone to set things up properly
// ...
): MyApplicationComponent
}
}After that, you can easily inject into any Android class (see below).
Unlike traditional Dagger, you do not need to define or instantiate Dagger components directly. Instead, we offer predefined components that are generated for you. Whetstone comes with a built-in set of components (and corresponding scope annotations) that are automatically integrated to the Android Framework. As expected, a binding in a child component can have dependencies on any binding in an ancestor component.
Component lifetimes are generally bounded by the creation and destruction of a corresponding instance of an important event. The table below lists the scope annotation and bounded lifetime for each component.
| Component | Scope | Created At | Destroyed At |
|---|---|---|---|
| ApplicationComponent | @ApplicationScope | Application#onCreate | Application#onTerminate |
| ActivityComponent | @ActivityScope | Activity#onCreate | Activity#onDestroy |
| FragmentComponent | @FragmentScope | FragmentFactory#instantiate | Fragment#onDestroy |
| ViewModelComponent | @ViewModelScope | ViewModelProvider.Factory#create | ViewModel#onCleared |
| ViewComponent | @ViewScope | View#init | View#finalize |
Applications support field/method injection with Whetstone. Constructor injection is not supported here because the instantiation of applications is completely managed by the system
@ContributesAppInjector
class MyApplication : Application(), ApplicationComponentOwner {
override val applicationComponent by lazy {
TODO("Create application component.")
}
@Inject
lateinit var dependency: MyDependency
fun onCreate() {
Whetstone.inject(this)
super.onCreate()
}
}Similar to applications, activities only support field/method injection
@ContributesActivityInjector
class MainActivity : AppCompatActivity() {
@Inject
lateinit var dependency: MyDependency
// Get the contributed ViewModel
// We automatically handle process death and saved state handle wiring
private val viewModel by injectedViewModel<MyViewModel>()
override fun onCreate(savedInstanceState: Bundle?) {
Whetstone.inject(this)
super.onCreate(savedInstanceState)
}
}Services should be generally avoided when possible. For most cases, work manager can be a great alternative and is highly recommended. See the workmanager section for more details about how to use it with Whetstone
@ContributesServiceInjector
class MyService : Service() {
@Inject
lateinit var dependency: MyDependency
override fun onCreate() {
Whetstone.inject(this)
super.onCreate()
}
}Disclaimer: View injection should be avoided by all means. This provision is considered legacy and may be completely removed in a later version of Whetstone.
@ContributesViewInjector
class MyView @JvmOverloads constructor(
context: Context,
attrs: AttributeSet? = null,
) : View(context, attrs) {
@Inject
lateinit var dependency: MainDependency
init {
if (!isInEditMode) {
Whetstone.inject(this)
}
}
}Fragments support only construction injection, exclusively. This is possible because we are able to hook into the system to influence exactly how fragments should be created. To achieve this, the activity hosting the fragment must install Whetstone's fragment factory.
class MyActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
Whetstone.inject(this)
super.onCreate(savedInstanceState)
}
}Then you're able to use the injected fragments with as many constructor arguments as necessary, as long as all these dependencies can be satisfied by dependency injection.
@ContributesFragment
class MyFragment @Inject constructor(
private val dependency: MyDependency,
private val anotherDependency: AnotherDependency,
): Fragment() {
// Get the contributed ViewModel
// We automatically handle process death and saved state handle wiring
private val viewModel by injectedViewModel<MyViewModel>()
private val activityViewModel by injectedActivityViewModel<ActivityViewModel>()
}Note that all injected fragments must be created via the fragment manager. For example:
val myFragment = fragmentManager.instantiate<MyFragment>()For fragments that don't require any external dependencies, the simple no-arg constructor can still be used, and we gracefully fallback to the default behavior
Important: A Fragment should NEVER be scoped. The Android Framework controls the Lifecycle of ALL Fragments.
Like fragments, view models also support full constructor injection
@ContributesViewModel
class MyViewModel @Inject constructor(
private val savedStateHandle: SavedStateHandle,
): ViewModel()Important: A ViewModel should NEVER be scoped. The Android Framework controls the Lifecycle of ALL ViewModels.
Workmanager integration is an extra add-on, and must be enabled explicitly in your build.gradle file before use:
whetstone {
addOns.workManager.set(true)
}This will automatically install Whetstone's worker factory (replacing the default factory), so that you can immediately start taking advantage of injected workers
@ContributesWorker
class UploadWorker @Inject constructor(
@ForScope(WorkerScope::class) context: Context,
workerParameters: WorkerParameters,
private val dependency: MyDependency,
): Worker(appContext, workerParameters)To disable automatic initialization, you can remove the initializer from your AndroidManifest.xml
<provider
android:name="androidx.startup.InitializationProvider"
android:authorities="${applicationId}.androidx-startup"
android:exported="false"
tools:node="merge">
<meta-data
android:name="com.deliveryhero.whetstone.worker.WhetstoneWorkerInitializer"
android:value="androidx.startup"
tools:node="remove" />
</provider>However, you must make sure to install Whetstone's worker factory before the first call to WorkManager#getInstance to avoid breaking the integration. Whetstone provides an injectable WorkerFactory that can be used to configure the work manager. For example, you can update your application class to implement work manager's Configuration.Provider and supply Whetstone's WorkerFactory to the configuration builder
See the official documentation for more details
Compose integration is an extra add-on, and must be enabled explicitly in your build.gradle file before use:
whetstone {
addOns.compose.set(true)
}Currently, this artefact only exposes APIs for injecting ViewModels that have been contributed to Whetstone
@Composable
fun MyScreen(viewModel: MyViewModel = injectedViewModel()) {
// injectedViewModel takes care of providing the VM instance directly to this function
}Copyright 2021 Delivery Hero, GmbH.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
