Kotlin Dagger 2 ContributesAndroidInjector 为模块提供活动

最小化样板文件的一种方法是创建一个通用ActivityModule，然后 for each Activity创建一个特定的小模块.

// Abstract class so you don't have to provide an instance
@Module
abstract class ActivityModule {

    // No need for ActivityScope: You're always binding to the same Activity, so
    // there's no reason to have Dagger save your Context instance in a Provider.
    @Binds @ActivityContext
    abstract fun providesContext(activity: Activity): Context

    // This doesn't *have* to be in a companion object, but that way
    // Android can do a static dispatch instead of a virtual method dispatch.
    // If you don't need that, just skip the constructor arguments and make these
    // normal methods and you'll be good to go.
    companion object {
        @Provides @ActivityContext
        fun providesLayoutInflater(activity: Activity): LayoutInflater = 
            activity.layoutInflater

        @Provides @ActivityContext
        fun providesResources(activity: Activity): Resources = activity.resources
    }
}

(在2.26之前的Dagger版本中，您可能需要在您的同伴对象上添加@Module，在您的@JvmStatic上添加@this previous revision中提供的方法.自2020年1月的Dagger 2.26以来，这些都不是必需的.谢谢arekolek！)

以及你的模块:

@Module
internal abstract class AppActivityModule {

    @Module
    internal interface WelcomeActivityModule {
      // The component that @ContributesAndroidInjector generates will bind
      // your WelcomeActivity, but not your Activity. So just connect the two,
      // and suddenly you'll have access via injections of Activity.
      @Binds fun bindWelcomeActivity(activity: WelcomeActivity) : Activity
    }

    @ContributesAndroidInjector(
        modules = [ActivityModule::class, WelcomeActivityModule::class])
    abstract fun contributeWelcomeActivityInjector(): WelcomeActivity
}

Note that though this works for Activity, Service, BroadcastReceiver, and others, you might not want to be so quick about it for Fragment. This is because dagger.android handles fragment hierarchies with parent fragments, so from within a child component you might have access to YourApplication, YourActivity, YourParentFragment, and YourChildFragment, and all of their components. If something in YourChildFragmentComponent depends on an unqualified Fragment, it would be ambiguous whether it really wants YourParentFragment or YourChildFragment. That said, this design does make sense for Activities and certain Fragments, so it makes sense to use it (cautiously).

@ActivityContext人在这里干什么？

@ActivityContext这里是您要定义的qualifier annotation，您可以使用它来区分Dagger和其他DI框架中相同类型的绑定，可能是@ApplicationContext Context对@ActivityContext Context.可以不使用它来try 它，但我强烈建议保留它，并避免绑定不合格的上下文:应用程序和活动上下文可能不同，尤其是在多屏幕或自动环境中，为了获得正确的资源和数据，您应该准确地了解您使用的内容.你可以以this one为例.