Following on from an official site of the Dagger, Hilt is built on top of the popular Dependency Injection (DI) library Dagger to provides a standard way to incorporate Dagger dependency injection into an Android application.

˚Following从的官方网站匕首，刀柄是建立在流行的依赖注入的顶部(DI)库匕首提供了一个标准的方法，将匕首依赖注入到一个Android应用程序。

The goals of Hilt are:

Hilt的目标是：

- To simplify Dagger-related infrastructure for Android apps.- To create a standard set of components and scopes to ease setup, readability/understanding, and code sharing between apps.- To provide an easy way to provision different bindings to various build types (e.g. testing, debug, or release).

-为Android应用程序简化与Dagger相关的基础结构。-创建一组标准的组件和范围以简化应用程序之间的设置，可读性/理解和代码共享。例如测试，调试或发布)。

If you are unfamiliar with Dagger, please checkout a series which I think it is very detailed and easiest to understand to start with Dagger.

如果您不熟悉Dagger，请查看一系列我认为非常详细且最容易理解的Dagger系列。

• Dagger 2. Part I. Basic principles, graph dependencies, scopes.

  Dagger 2.第一部分。基本原理，图形依赖关系，范围。

Until now, we have had many introductions and tutorials to setup, migrate,… to use Hilt.

到现在为止，我们已经有许多介绍和教程来进行设置，迁移……以使用Hilt。

• Dependency injection with Hilt.

  Hilt的依赖注入。

• Migrating your Dagger app to Hilt.

  将您的Dagger应用迁移到Hilt 。

But we have very few articles on how to work with Hilt in the Dynamic Feature world.

但是，在动态功能世界中，关于如何使用Hilt的文章很少。

In this post, we will see the Hilt configuration way in a project use the dynamic feature module (DFM) and how to deal with @ViewModelInject to inject SavedStateHandle into a ViewModel in DFM.

在本文中，我们将看到项目中使用动态功能模块( DFM )的Hilt配置方式，以及如何处理@ViewModelInject将SavedStateHandle注入DFM中的ViewModel中。

Nowaday in the Android’s products developement, the choice of modularization architecture (multi-module) to get many advantages is obvious. Applying DI for that architecture to manage instances by each scope is also obvious. If your multi-module project is composed of regular Gradle modules, then you can use Dagger by in the usual way. However, if your project is composed of multi DFM module then everything will be different.

如今，在Android产品的开发中，获得许多优势的模块化架构(多模块)的选择显而易见。 将DI应用于该体系结构以按每个作用域管理实例也很明显。 如果您的多模块项目由常规Gradle模块组成，则可以按常规方式使用Dagger。 但是，如果您的项目是由多个DFM模块组成的，那么一切都会有所不同。

In DFM, the way that modules usually depend on each other is inverted. Therefore, Hilt cannot process annotations in feature modules. You must use Dagger to perform dependency injection in your DFM.

在DFM中，模块通常相互依赖的方式是相反的。 因此，Hilt无法处理功能模块中的注释。 您必须使用Dagger在DFM中执行依赖项注入。

DI in DFM is still a complex technique, partly because it is abstract. Before Hilt was born, one of the most Dagger implementations in DFM is:

DFM中的DI仍然是一项复杂的技术，部分是因为它是抽象的。 在Hilt出生之前，DFM中最Dagger的实现之一是：

• Gapo Dashboard

  Gapo资讯主页

Now, Hilt has arrived to reduce more Java/Kotlin boilerplate and it is the future.

现在，Hilt已经到来以减少更多Java / Kotlin样板，这是未来。

It is time to play Hilt together.

是时候一起玩Hilt了。

1.使用3个模块创建一个新项目：应用，核心(库模块)和功能(功能模块)。 (1. Create a new project with 3 modules: app, core (Library Module) and feature (Feature Module).)

App depends on Core. Feature depends on App and Core.

应用取决于Core。 功能取决于App和Core。

2.添加依赖项。 (2. Adding dependencies.)

• First, add the hilt-android-gradle-plugin plugin to your project's root build.gradle file:

  首先，将hilt-android-gradle-plugin插件添加到项目的根build.gradle文件中：

buildscript {    ...    dependencies {        ...

    }}

• Then, apply the Gradle plugin and add these dependencies in your modules’ .../build.gradle file:

  然后，应用Gradle插件，并将这些依赖项添加到模块的.../build.gradle文件中：

...apply plugin: 'kotlin-kapt'apply plugin: 'dagger.hilt.android.plugin' // not needed for feature moduleandroid {    ...}dependencies {

    implementation 'androidx.hilt:hilt-common:1.0.0-alpha02'    implementation 'androidx.hilt:hilt-lifecycle-viewmodel:1.0.0-alpha02'    kapt 'androidx.hilt:hilt-compiler:1.0.0-alpha02'}

3.编码 (3. Coding)

• In app module:

  在应用程序模块中：

@HiltAndroidApp
class MyApplication : Application() {@Inject@UserModelSingletonQualifierlateinit var singletonUserModel: UserModeloverride fun onCreate() {super.onCreate()  singletonUserModel.value += "MyApplication"}
}

• In core module

  在核心模块中

@Module
@InstallIn(ApplicationComponent::class)
object CoreModule {@Provides@Singleton@UserModelSingletonQualifierfun provideUserModel() = UserModel(value = "Singleton")
}

Let run app, everything is fine. Code is really very concise.

让我们运行应用程序，一切都很好。 代码真的非常简洁。

Then do the same thing for FeatureActivity in feature module, we will get a exception because Hilt cannot process annotations in feature modules.

然后对功能模块中的FeatureActivity做同样的事情，我们将得到一个例外，因为Hilt无法处理功能模块中的注释。

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.kienht.dagger.hilt.dfm/com.kienht.dagger.hilt.feature.Feature2Activity}: java.lang.ClassCastException: com.kienht.dagger.hilt.dfm.DaggerMyApplication_HiltComponents_SingletonC$ActivityRetainedCImpl$ActivityCImpl cannot be cast to com.kienht.dagger.hilt.feature.FeatureActivity_GeneratedInjector

We also can find this issue in Dagger repository.

我们也可以在Dagger存储库中找到此问题。

To resolve this issue we need to manual providing dependencies.

要解决此问题，我们需要手动提供依赖项。

• In core module:

  在核心模块中：

We need to expose dependencies for feature module depend on them. And also create a custom SavedStateViewModelFactory to inject anything into ViewModel.

我们需要公开功能模块所依赖的依赖关系。 并且还创建一个自定义SavedStateViewModelFactory，以将任何内容注入ViewModel中。

@Module
@InstallIn(ActivityComponent::class)
object ActivityViewModelModule {@Providesfun provideSavedStateViewModelFactory(application: Application,activity: Activity,viewModelFactories: @JvmSuppressWildcards Map<String, Provider<ViewModelAssistedFactory<out ViewModel>>>,): DFMSavedStateViewModelFactory {val owner = activity as SavedStateRegistryOwnerval defaultArgs = activity.intent?.extrasval delegate = SavedStateViewModelFactory(application, owner, defaultArgs)return DFMSavedStateViewModelFactory(owner, defaultArgs, delegate, viewModelFactories)}
}

• In feature module

  在功能模块中

class FeatureActivity : AppCompatActivity(R.layout.feature_activity) {@Inject@UserModelSingletonQualifierlateinit var singletonUserModel: UserModel@Injectlateinit var savedStateViewModelFactory: DFMSavedStateViewModelFactoryprivate val featureActivityViewModel by viewModels<FeatureActivityViewModel> { savedStateViewModelFactory }override fun onCreate(savedInstanceState: Bundle?) {inject()super.onCreate(savedInstanceState)Timber.e("singleton userModel = $singletonUserModel")singletonUserModel.value += " => FeatureActivity"Timber.e("userModel = ${featureActivityViewModel.userModel}")}
}

We have done. Hilt is so easy to use. I would like to emphasize again, Hilt is future.

我们做完了。 刀柄非常易于使用。 我想再次强调一下，希尔特是未来。

There are some things to note:

有一些注意事项：

1. Any feature modules need to shared objects in Application scope have to depend on ModuleDependencies. For example, the CoreModuleDependencies, we can expose any objects which are provided through Modules are installed in ApplicationComponent. Then every object needed to inject will be injected from EntryPoint.

   需要在应用程序范围内共享对象的任何功能模块都必须依赖ModuleDependencies 。 例如，对于CoreModuleDependencies ，我们可以公开通过ApplicationComponent中安装的模块提供的任何对象。 然后将从EntryPoint注入需要注入的每个对象。

2. FeatureActivityModule includes the FeatureActivityViewModel_HiltModule which is generated through processing @ViewModelInject annotation by Hilt to provide a FeatureActivityViewModel instance.

   FeatureActivityModule包含FeatureActivityViewModel_HiltModule ，它是通过Hilt处理@ViewModelInject批注以提供FeatureActivityViewModel实例而生成的。

3. To retrieve a ViewModel instance in feature module we needed a custom ViewModelFactory and a ViewModelStoreOwner. DFMSavedStateViewModelFactory take responsibility for creating and injection and especially for SavedStateHandle. ViewModelStoreOwner depends on determined scope (activity, fragment or navigation graph).

   要在功能模块中检索ViewModel实例，我们需要一个自定义的ViewModelFactory和一个ViewModelStoreOwner。 DFMSavedStateViewModelFactory负责创建和注入，尤其是SavedStateHandle 。 ViewModelStoreOwner取决于确定的范围(活动，片段或导航图)。

More details about dealing Hilt in Fragment to use the shared ViewModel in activity scope or navigation graph scope will be described in this repository. Thanks for reading!

在此存储库中将描述有关在Fragment中处理Hilt以在活动范围或导航图范围中使用共享ViewModel的更多详细信息。 谢谢阅读！