如何使活动正确地观察生命周期事件

目前,我需要执行一些操作,当

• 应用程序已启动。
• 应用程序已退出。
• 但不是在活动娱乐,配置改变…

因此,到目前为止,下面的代码片段非常适合我。我从普通软件中学到了这种把戏- https://commonsware.com/AndroidArch/previews/other-lifecycle-owners 和 https://proandroiddev.com/react-to-app-foreground-and-background-events-with-processlifecycleowner-96278e5816fa

wenoteapplication.java语言

public class WeNoteApplication extends Application {

    public static class AppLifecycleObserver implements DefaultLifecycleObserver {
        @Override
        public void onResume(LifecycleOwner owner) {
            // Do something when the application launched.
            // But not during activity recreation, configuration change, ...
        }

        @Override
        public void onPause(LifecycleOwner owner) {
            // Do something when the application quit.
            // But not during activity recreation, configuration change, ...
        }
    }

    private static final AppLifecycleObserver appLifecycleObserver = new AppLifecycleObserver();

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

        initLifecycleObserver();
    }

    private void initLifecycleObserver() {
        Lifecycle lifecycle = ProcessLifecycleOwner.get().getLifecycle();
        lifecycle.removeObserver(appLifecycleObserver);
        lifecycle.addObserver(appLifecycleObserver);
    }
}   

但是,我还需要通过使用 Activity , Fragment ,…例如,显示 DialogFragment .

对于我的入口点主 活动 ,这是我试过的。

public class MainActivity extends AppCompatActivity implements DefaultLifecycleObserver {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ProcessLifecycleOwner.get().getLifecycle().removeObserver(this);
        ProcessLifecycleOwner.get().getLifecycle().addObserver(this);

        setContentView(R.layout.activity_main);
    }

    @Override
    public void onResume(LifecycleOwner owner) {
        android.util.Log.i("CHEOK", "onResume LifecycleOwner called");
    }

    @Override
    public void onPause(LifecycleOwner owner) {
        android.util.Log.i("CHEOK", "onPause LifecycleOwner called");
    }

    @Override
    public void onCreate(LifecycleOwner owner) {
        android.util.Log.i("CHEOK", "onCreate LifecycleOwner called");
    }
}

由于以下观察结果,它不能按预期工作

当应用程序启动时

onCreate LifecycleOwner called
onResume LifecycleOwner called
onResume LifecycleOwner called    <-- Why onResume of LifecycleOwner is called twice??

当我转动装置时

onCreate LifecycleOwner called
onResume LifecycleOwner called    <-- Why onCreate and onResume of LifecyclOwner is called during configuration change?

使用LiveData重试

我试着用 LiveData 为了 AppLifecycleObserver 与…沟通 活动 . 但是,在配置更改期间, onResumeLiveData 重新创建的款待 活动 作为新的生命周期所有者。因此,它将再次触发它。

public class WeNoteApplication extends Application {

    public MutableLiveData<LifecycleOwner> onResumeLiveData = new MutableLiveData<>();

    public class AppLifecycleObserver implements DefaultLifecycleObserver {
        @Override
        public void onResume(LifecycleOwner owner) {
            // This will only be called during app launch, not configuration change.
            android.util.Log.i("CHEOK", "onResume callback happen in application");
            onResumeLiveData.setValue(owner);
            ...


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

        WeNoteApplication.instance().onResumeLiveData.observe(this, new Observer<LifecycleOwner>() {
            @Override
            public void onChanged(@Nullable LifecycleOwner lifecycleOwner) {
                // This will only be called during app launch
                // This will also be called during configuration change.
                android.util.Log.i("CHEOK", "onResume callback happen in activity");
            }
        });

所以,我有点困惑。正确的方法是什么? Activitly (或) 碎片 )观察 Lifecycle 事件?也就是说,在配置更改、活动重新创建等过程中,不应触发这些回调事件函数。