如何在LifecycleObserver中获取LifecycleOwner？

Question

我需要在LifecycleObserver中获取LifecycleOwner，以便将其传递给ViewModel观察者。

这是我的MainActivity，我在其中添加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);
        });

    }
}

- Alex G

Answer 1

您可以使用另一个签名来获取LifecycleOwner，例如：

public class MyLifecycleObserver implements LifecycleObserver {


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

- jaychang0917

---

@OnLifecycleEvent已被弃用。请参考https://developer.android.com/jetpack/androidx/releases/lifecycle#2.4.0-beta01。 - Akito

Answer 2

观察者方法可以接收零个或一个参数。如果使用（也就是说您也可以使用零个参数，但仅当使用参数时），第一个参数必须是LifecycleOwner类型。带有Lifecycle.Event.ON_ANY注解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) {
               //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
             }
}

- Abhishek Kumar

---

你能提供一个文档链接吗？ - pallgeuer

@pallgeuer https://developer.android.com/topic/libraries/architecture/lifecycle#lc - Abhishek Kumar

谢谢。我特别在寻找LifecycleOwner可以作为OnLifecycleEvent注释的函数的参数进行传递的文档。这个有文档记录吗？ - pallgeuer

@OnLifecycleEvent已被弃用。请参考https://developer.android.com/jetpack/androidx/releases/lifecycle#2.4.0-beta01。 - Akito

Answer 3

你不需要实现自己的LifecycleRegistry - 只需使用从AppCompatActivity可用的那个。

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());
  }
}

如果你将startFirebase调用和viewmodel observer分开，那么就可以直接在fragment中观察到viewmodel的变化，即：

当ON_START被发出时，MyLifecycleObserver开始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);
      });
  }

- Chris

---

@OnLifecycleEvent已被弃用。请参考https://developer.android.com/jetpack/androidx/releases/lifecycle#2.4.0-beta01。 - Akito

Answer 4

由于@OnLifecycleEvent已过时，我认为最好的方法是实现LifecycleObserver并覆盖生命周期方法：

class TestObserver: LifecycleObserver {

    override fun onCreate(owner: LifecycleOwner) {
        super.onCreate(owner)
        // your code
    }

    override fun onResume(owner: LifecycleOwner) {
        super.onResume(owner)
        // your code
    }
}

- Agna JirKon Rx

Answer 5

Abhishek Kumar的官方文档答案来自于这里：

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

以下是文件本身：

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

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

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

- Ray Yuan Liou

---

@OnLifecycleEvent已被弃用。请参考https://developer.android.com/jetpack/androidx/releases/lifecycle#2.4.0-beta01。 - Akito