了解用于 Android 开发的 Dagger 2

Question

这是我的代码，它基于互联网上的一些旧教程。 Dagger 2的主站点上应该有一些例子，我发现如何实现这一切真的很难理解。

要运行这么简单的应用程序确实需要大量工作。我有两个问题：

我是否必须在每个类中调用 DaggerLoggerComponent 我想获得一些组件，比如我的 Logger 类？

另外，我怎样才能使 Logger 类的范围成为单例？现在每个按钮单击都会创建一个新的记录器实例。

可能我不了解一些底层概念，我之前只在 Spring 中使用过依赖注入，这一切对我来说似乎很奇怪。

public class MainActivity extends AppCompatActivity {

    private Button button;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
    }

    private void init(){
        button = (Button)findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                LoggerComponent component = DaggerLoggerComponent.builder().loggerModule(new LoggerModule()).build();
                component.getLogger().log("Hello!",MainActivity.this);
            }
        });
    }

}


public class Logger {

    private static int i = 0;

    public Logger(){
        i++;
    }

    public static int getI() {
        return i;
    }

    public void log(String text, Context context){
        Toast.makeText(context,text+" "+i,Toast.LENGTH_SHORT).show();
    }
}


@Singleton
@Component(modules={LoggerModule.class})
public interface LoggerComponent {

    Logger getLogger();

}


@Module
public class LoggerModule {
    @Provides
    @Singleton
    Logger provideLogger(){
        return new Logger();
    }
}

Answer 1

答案是

public class MainActivity extends AppCompatActivity {
    @OnClick(R.id.button) //ButterKnife
    public void onClickButton() {
        logger.log("Hello!");
    }

    @Inject
    Logger logger;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Injector.INSTANCE.getApplicationComponent().inject(this);
        ButterKnife.bind(this);
    }

    @Override
    protected void onDestroy() {
        ButterKnife.unbind(this);
        super.onDestroy();
    }
}

public class Logger {
    private static int i = 0;

    private CustomApplication customApplication;

    public Logger(CustomApplication application) {
        this.customApplication = application;
        i++;
    }

    public static int getI() {
        return i;
    }

    public void log(String text){
        Toast.makeText(customApplication, text + " " + i,Toast.LENGTH_SHORT).show();
    }
}


public interface LoggerComponent {
    Logger logger();
}

@Module
public class ApplicationModule {
    private CustomApplication customApplication;

    public ApplicationModule(CustomApplication customApplication) {
        this.customApplication = customApplication;
    }

    @Provides
    public CustomApplication customApplication() {
        return customApplication;
    }
}

@Module
public class LoggerModule {
    @Provides
    @Singleton
    Logger provideLogger(){
        return new Logger();
    }
}


@Singleton
@Component(modules={LoggerModule.class, ApplicationModule.class})
public interface ApplicationComponent extends LoggerComponent {
    CustomApplication customApplication();

    void inject(MainActivity mainActivity);
}

public class CustomApplication extends Application {
    @Override
    public void onCreate() {
        super.onCreate();
        Injector.INSTANCE.initializeApplicationComponent(this);
    }
}

public enum Injector {
    INSTANCE;

    private ApplicationComponent applicationComponent;

    public ApplicationComponent getApplicationComponent() {
        return applicationComponent;
    }

    void initializeApplicationComponent(CustomApplication customApplication) {
        this.applicationComponent = DaggerApplicationComponent.builder()
            .applicationModule(new ApplicationModule(customApplication))
            .build();
    }
}

This is currently our Dagger2 architecture.

编辑：这是来自我们正在制作的应用程序中改造内容的实际代码：

public interface RecordingService {    
    ScheduledRecordsXML getScheduledRecords(long userId)
            throws ServerErrorException;
}

public class RecordingServiceImpl
        implements RecordingService {

    private static final String TAG = RecordingServiceImpl.class.getSimpleName();

    private RetrofitRecordingService retrofitRecordingService;

    public RecordingServiceImpl(RetrofitRecordingService retrofitRecordingService) {
        this.retrofitRecordingService = retrofitRecordingService;
    }

    @Override
    public ScheduledRecordsXML getScheduledRecords(long userId)
            throws ServerErrorException {
        try {
            return retrofitRecordingService.getScheduledPrograms(String.valueOf(userId));
        } catch(RetrofitError retrofitError) {
            Log.e(TAG, "Error occurred in downloading XML file.", retrofitError);
            throw new ServerErrorException(retrofitError);
        }
    }
}

@Module
public class NetworkClientModule {
    @Provides
    @Singleton
    public OkHttpClient okHttpClient() {
        OkHttpClient okHttpClient = new OkHttpClient();
        okHttpClient.interceptors().add(new HeaderInterceptor());
        return okHttpClient;
    }
}

@Module(includes = {NetworkClientModule.class})
public class ServiceModule {
    @Provides
    @Singleton
    public RecordingService recordingService(OkHttpClient okHttpClient, Persister persister, AppConfig appConfig) {
        return new RecordingServiceImpl(
                new RestAdapter.Builder().setEndpoint(appConfig.getServerEndpoint())
                        .setConverter(new SimpleXMLConverter(persister))
                        .setClient(new OkClient(okHttpClient))
                        .setLogLevel(RestAdapter.LogLevel.NONE)
                        .build()
                        .create(RetrofitRecordingService.class));
    }

    //...
}

public interface RetrofitRecordingService {
    @GET("/getScheduledPrograms")
    ScheduledRecordsXML getScheduledPrograms(@Query("UserID") String userId);
}

public interface ServiceComponent {
    RecordingService RecordingService();

    //...
}

public interface AppDomainComponent
        extends InteractorComponent, ServiceComponent, ManagerComponent, ParserComponent {
}

@Singleton
@Component(modules = {
        //...
        InteractorModule.class,
        ManagerModule.class,
        ServiceModule.class,
        ParserModule.class
    //...
})
public interface ApplicationComponent
        extends AppContextComponent, AppDataComponent, AppDomainComponent, AppUtilsComponent, AppPresentationComponent {
    void inject(DashboardActivity dashboardActivity);
    //...
}

Answer 2

我是否必须在每个类中调用 DaggerLoggerComponent 我想获得一些组件，比如我的 Logger 类？

是的，适用于系统创建的所有类，如应用程序、活动和服务。但是对于您自己的课程，您不需要它。只需使用 @inject 注释您的构造函数，dagger 将提供您的依赖项。

另外，我怎样才能使 Logger 类的范围成为单例？正确的 现在每个按钮单击都会创建一个新的记录器实例。

您的单例设置是正确的。但是您必须在创建活动（onCreate）后初始化一次组件，以便让匕首注入所有字段。如果您不需要立即使用 Logger 对象，也可以使用延迟注入功能。

    @Inject
    Logger logger;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        LoggerComponent component = DaggerLoggerComponent.builder().loggerModule(new LoggerModule()).build();

        component.inject(this);

        init();
    }

然后您可以访问您的对象，而无需从组件中获取引用：

private void init(){
        button = (Button)findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                logger.log("Hello!",MainActivity.this);
            }
        });
    }

总结： 您必须在所有使用字段注入的类中初始化组件。

更新： 要进行实际的注入，您必须在组件中声明 inject() 方法，并且 dagger 会自动实现它。此方法将负责提供任何带有 @Inject 注释的对象。