提供一個HttpObject對象

public class HttpObject {
}

提供一個Module

@Singleton
@Module
public class HttpModule{
    @Singleton
    @Provides
    public HttpObject provederHttpObject(){
        return new HttpObject();
    }
}

單例類的使用需要在@Module修飾的類和@Provides修飾的方法上分別添加@Singleton。

提供一個Component

@Singleton
@Component(modules = {HttpModule.class,DatabaseModule.class})
public interface MyComponent 
    void injectMainActivity(MainActivity mainActivity);
    void injectSecondActivity(SecondActivity secondActivity);
}

同時在@Component修飾的Componet上添加@Singleton。

從MainActivity跳轉(zhuǎn)到SecondActivity，來觀察HttpObject 是否是一個對象。

MainActivity.java

public class MainActivity extends AppCompatActivity {
    @Inject
    HttpObject httpObject1;
    @Inject
    HttpObject httpObject2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        //第一種注入方法
        DaggerMyComponent.create().injectMainActivity(this);
        //第二種注入方法
//        DaggerMyComponent.builder().httpModule(new HttpModule())
//                .build()
//                //到這里就已經(jīng)產(chǎn)生了module和component對象
//                .injectMainActivity(this);

        Log.i("log",httpObject1.hashCode()+"");//189244270
        Log.i("log",httpObject2.hashCode()+"");//189244270
        Log.i("log",databaseObject.hashCode()+"");//69880476
    }

    public void jump(View view) {
        this.startActivity(new Intent(this,SecondActivity.class));
    }
}

SecondActivity.java

public class SecondActivity extends AppCompatActivity {
    @Inject
    HttpObject httpObject;

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

        DaggerMyComponent.create().injectSecondActivity(this);
        Log.i("log",httpObject.hashCode()+"");//115744208
    }
}

可以看到，在MainActivity中HttpObject的HashCode是一樣的，說明是一個對象；而在SecondActivity中HttpObject的HashCode發(fā)生了變化，和MainActivity是不一樣的，這就是局部單例。

下面來把局部單例變?yōu)槿謫卫?/p>

其它的類都不需要修改，只需要在Application中操作即可。
MyApplication.java

public class MyApplication extends Application {
    private MyComponent myComponent;
    @Override
    public void onCreate() {
        super.onCreate();
        myComponent= DaggerMyComponent.builder()
                .httpModule(new HttpModule())
//                .presenterComponent(DaggerPresenterComponent.builder()
//                .presenterModule(new PresenterModule())
                .build();
    }
    public MyComponent getAppComponent(){
        return myComponent;
    }
}

在Activitie中使用的如下：

((MyApplication)getApplication()).getAppComponent().injectMainActivity(this);