Dagger 2 注入 Android 应用程序上下文

Question

我正在使用 Dagger 2 并且可以正常工作，但是我现在需要访问 Android 应用程序上下文。

我不清楚如何注入和访问上下文。我尝试按以下方式执行此操作：

@Module
public class MainActivityModule {    
    private final Context context;
    
    MainActivityModule(Context context) {
        this.context = context;
    }

    @Provides @Singleton
    Context provideContext() {
        return context;
    }
}

但是这会导致以下异常：

java.lang.RuntimeException：无法创建应用程序：java.lang.IllegalStateException：必须设置 mainActivityModule

如果我检查 Dagger 生成的代码，这里会引发此异常：

public Graph build() {  
    if (mainActivityModule == null) {
        throw new IllegalStateException("mainActivityModule must be set");
    }
    return new DaggerGraph(this);
}

我不确定这是否是注入上下文的正确方法 - 任何帮助将不胜感激。

Answer 1

未正确构建应用程序组件，需要传入应用程序。这个 Dagger 2 示例完美地展示了如何做到这一点：https://github.com/google/dagger/tree/master/examples/android-simple/src/main/java/com/example/dagger/simple

更新：
工作链接：https://github.com/yongjhih/dagger2-sample/tree/master/examples/android-simple/src/main/java/com/example/dagger/simple

Answer 2

@Module
public class MainActivityModule {    
    private final Context context;

    public MainActivityModule (Context context) {
        this.context = context;
    }

    @Provides //scope is not necessary for parameters stored within the module
    public Context context() {
        return context;
    }
}

@Component(modules={MainActivityModule.class})
@Singleton
public interface MainActivityComponent {
    Context context();

    void inject(MainActivity mainActivity);
}

然后

MainActivityComponent mainActivityComponent = DaggerMainActivityComponent.builder()
    .mainActivityModule(new MainActivityModule(MainActivity.this))
    .build();

Answer 3

我花了一段时间才找到合适的解决方案，因此认为这可能会为其他人节省一些时间，据我所知，这是当前 Dagger 版本 (2.22.1) 的首选解决方案。

在以下示例中，我需要Application 的Context 来创建RoomDatabase（发生在StoreModule）。

如果您发现任何错误或错误，请告诉我，以便我也学习:)

组件：

// We only need to scope with @Singleton because in StoreModule we use @Singleton
// you should use the scope you actually need
// read more here https://google.github.io/dagger/api/latest/dagger/Component.html
@Singleton
@Component(modules = { AndroidInjectionModule.class, AppModule.class, StoreModule.class })
public interface AwareAppComponent extends AndroidInjector<App> {

    // This tells Dagger to create a factory which allows passing 
    // in the App (see usage in App implementation below)
    @Component.Factory
    interface Factory extends AndroidInjector.Factory<App> {
    }
}

应用模块：

@Module
public abstract class AppModule {
    // This tell Dagger to use App instance when required to inject Application
    // see more details here: https://google.github.io/dagger/api/2.22.1/dagger/Binds.html
    @Binds
    abstract Application application(App app);
}

存储模块：

@Module
public class StoreModule {
    private static final String DB_NAME = "aware_db";

    // App will be injected here by Dagger
    // Dagger knows that App instance will fit here based on the @Binds in the AppModule    
    @Singleton
    @Provides
    public AppDatabase provideAppDatabase(Application awareApp) {
        return Room
                .databaseBuilder(awareApp.getApplicationContext(), AppDatabase.class, DB_NAME)
                .build();
    }
}

应用：

public class App extends Application implements HasActivityInjector {

    @Inject
    DispatchingAndroidInjector<Activity> dispatchingAndroidInjector;

    @Override
    public void onCreate() {
        super.onCreate();

        // Using the generated factory we can pass the App to the create(...) method
        DaggerAwareAppComponent.factory().create(this).inject(this);
    }

    @Override
    public AndroidInjector<Activity> activityInjector() {
        return dispatchingAndroidInjector;
    }
}

Answer 4

我读过这篇文章，很有帮助。

https://medium.com/tompee/android-dependency-injection-using-dagger-2-530aa21961b4

示例代码。

更新：我从 AppComponent.kt 中删除了这些行，因为不是必需的

fun context(): Context
fun applicationContext(): Application

AppComponent.kt

   @Singleton
    @Component(
        modules = [
            NetworkModule::class,
            AppModule::class
        ]
    )
    interface AppComponent {
        fun inject(viewModel: LoginUserViewModel)
    }

AppModule.kt

@Module
class AppModule(private val application: Application) {

    @Provides
    @Singleton
    fun providesApplication(): Application = application

    @Provides
    @Singleton
    fun providesApplicationContext(): Context = application

    @Singleton
    @Provides
    fun providesNetworkConnectivityHelper(): NetworkConnectivityHelper{
        return NetworkConnectivityHelper(application.applicationContext)
    }
}

NetworkConnectivityHelper.kt

并且只添加了@Inject构造函数来传递Context

class NetworkConnectivityHelper @Inject constructor(context: Context) {

    private val connectivityManager =
        context.getSystemService(CONNECTIVITY_SERVICE) as ConnectivityManager

    @Suppress("DEPRECATION")
    fun isNetworkAvailable(): Boolean {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            val nc = connectivityManager.getNetworkCapabilities(connectivityManager.activeNetwork)

            nc != null
                    && nc.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)
                    && nc.hasCapability(NetworkCapabilities.NET_CAPABILITY_VALIDATED)
        }

        val networkInfo = connectivityManager.activeNetworkInfo
        return networkInfo != null && networkInfo.isConnected
    }
}

应用类.kt

class App : Application() {

    lateinit var appComponent: AppComponent

    override fun onCreate() {
        super.onCreate()
        this.appComponent = this.initDagger()
    }

    private fun initDagger() = DaggerAppComponent.builder()
        .appModule(AppModule(this))
        .build()
}

最后在我的活动中我注入了我的助手

 @Inject lateinit var networkConnectivity: NetworkConnectivityHelper

还有耶！它对我有用。

Answer 5

也许我们可以注入如下所示的上下文：

应用程序组件

@Component(
    modules = [
        (ApplicationModule::class),
        (AndroidSupportInjectionModule::class),
        (UiBindingModule::class)
    ]
)
interface ApplicationComponent : AndroidInjector<AndroidApplication> {

    override fun inject(application: AndroidApplication)

    @Component.Builder
    interface Builder {

        @BindsInstance
        fun application(application: AndroidApplication): Builder

        @BindsInstance
        fun context(context: Context): Builder

        fun build(): ApplicationComponent
    }
}

自定义应用扩展匕首应用

class AndroidApplication : DaggerApplication() {

    override fun applicationInjector(): AndroidInjector<out DaggerApplication> {
        return DaggerApplicationComponent.builder().application(this).context(this).build()
    }
}

应用模块示例

@Module
abstract class ApplicationModule {

    /**
     * Binds a background thread executor, which executes threads from a thread pool
     * @param jobExecutor
     * @return
     */
    @Binds
    internal abstract fun provideThreadExecutor(jobExecutor: JobExecutor): ThreadExecutor

    /**
     * Binds main ui looper thread
     * @param uiThread
     * @return
     */
    @Binds
    internal abstract fun providePostExecutionThread(uiThread: UIThread): PostExecutionThread

}

UI BindingModule 示例

@Module
abstract class UiBindingModule {

    @ContributesAndroidInjector(modules = [(MainActivityModule::class)])
    internal abstract fun mainActivity(): MainActivity

    @ContributesAndroidInjector(modules = [(MapFragmentModule::class)])
    internal abstract fun mapFragment(): MapFragment

}