Question

我需要在LifecycleObserver中获得LifecycleOwner，以将其传递给ViewModel观察器。

这是我的MainActivity，如果我添加了LifecycleObserver。

public class MainActivity extends AppCompatActivity implements LifecycleOwner{

    private LifecycleRegistry mLifecycleRegistry;


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

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .replace(R.id.container, MainFragment.newInstance())
                    .commitNow();
        }

        mLifecycleRegistry=new LifecycleRegistry(this);
        mLifecycleRegistry.markState(Lifecycle.State.CREATED);
        getLifecycle().addObserver(new MyLifecycleObserver());
    }


    @NonNull
    @Override
    public Lifecycle getLifecycle() {
        return mLifecycleRegistry;
    }

}

这是我的观察者，我需要LifecycleOwner。

public class MyLifecycleObserver implements LifecycleObserver {


    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    public void onStartListener(){

        FirebaseMassage.startFirebase();

        MainFragment.massageViewModel.getMassage().observe(/*here I need the LifecycleOwner*/, textMassage -> {
            FirebaseMassage.updateFirebaseMassage(textMassage);
        });

    }
}

Answer 1

您可以使用另一个签名来获得LifecycleOwner，例如：

public class MyLifecycleObserver implements LifecycleObserver {


    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    public void onStartListener(LifecycleOwner owner){
        ... 
    }
}

Answer 2

您不需要实现自己的LifecycleRegistry-只需使用AppCompatActivity提供的一个即可

public class MainActivity extends AppCompatActivity {
  @Override
  protected void onCreate(@Nullable Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);

      setContentView(R.layout.activity_main);

      if (savedInstanceState == null) {
          getSupportFragmentManager().beginTransaction()
                  .replace(R.id.container, MainFragment.newInstance())
                  .commitNow();
      }

      getLifecycle().addObserver(new MyLifecycleObserver());
  }
}

如果将startFirebase调用和viewmodel观察器分开，则可以直接在片段中观察viewmodel的变化，即

MyLifecycleObserver在发出ON_START时启动firebase调用。

public class MyLifecycleObserver implements LifecycleObserver {
    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    public void onStartListener(){
        FirebaseMassage.startFirebase();
    }
}

MainFragment直接观察ViewModel。

public class MainFragment extends Fragment {

  @Override
  public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
      super.onViewCreated(view, savedInstanceState);
      massageViewModel.getMassage().observe(this, textMassage -> {
          FirebaseMassage.updateFirebaseMassage(textMassage);
      });
  }

Answer 3

观察者方法可以接收零或一个参数。如果使用了（意味着您也可以使用零参数，但使用 IFF 参数），则第一个参数必须为 LifecycleOwner 类型。带有 Lifecycle.Event.ON_ANY 注释的方法可以接收第二个参数，该参数的类型必须为 Lifecycle.Event 。

class TestObserver implements LifecycleObserver {
         @OnLifecycleEvent(ON_CREATE)
         void onCreated(LifecycleOwner source) {
               //one argument possible
              }
         @OnLifecycleEvent(ON_START)
         void onCreated() {
              //no argument possible
             }
         @OnLifecycleEvent(ON_ANY)
         void onAny(LifecycleOwner source, Event event) {
             //two argument possible only for ON_ANY event
             }
}

Answer 4

Abhishek Kumar 回答的官方文档来自这里：

https://developer.android.com/reference/androidx/lifecycle/Lifecycle#subclasses-direct:~:text=Observer%20methods%20can%20receive%20zero%20or%20one%20argument

这是文档本身：

观察者方法可以接收零个或一个参数。如果使用，第一个参数必须是 LifecycleOwner 类型。

用 Lifecycle.Event.ON_ANY 注释的方法可以接收第二个参数，该参数必须是 Lifecycle.Event 类型。

 class TestObserver implements LifecycleObserver {
   @OnLifecycleEvent(ON_CREATE)
   void onCreated(LifecycleOwner source) {}
   @OnLifecycleEvent(ON_ANY)
   void onAny(LifecycleOwner source, Event event) {}
 }

如何在LifecycleObserver中获取LifecycleOwner？

4 个答案: