Fragment lifecycle events in LifeCycleAware Fragment

问题

I have a lifecycle aware fragment and a LifecycleObserver class

        public class MyFragment extends Fragment {
            @Override
            public void onCreate(@Nullable Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                new MyObserver(this);

            }

            @Nullable
            @Override
            public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
                return inflater.inflate(R.layout.activity_main, container, false);
            }
        }

Following is my Observer class where it logs all the fragment events propery

        public class MyObserver implements LifecycleObserver {
            private static final String TAG = "MyObserver";
            public MyObserver(LifecycleOwner lifecycleOwner) {
                lifecycleOwner.getLifecycle().addObserver(this);
            }

            @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
            public void onCreate(){
                Log.d(TAG, "onCreate: ");
            }

            @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
            public void onPause(){
                Log.d(TAG, "onPause: ");
            }

            @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
            public void onDestroy(){
                Log.d(TAG, "onDestroy: ");
            }

            @OnLifecycleEvent(Lifecycle.Event.ON_START)
            public void onStart(){
                Log.d(TAG, "onStart: ");
            }

        }

I want to listen to fragment specific lifecycle events like onDestroyView and onActivityCreated but these events are not there in

Lifecycle.Event. It contains only activity events. How can I listen for fragment events in my observer

回答1:

You can observe the fragment's viewLifecycleOwner lifecycle.

viewLifecycleOwner.lifecycle.addObserver(yourObserverHere)

Then the fragment's onDestroyView lifecyle method is tied to the @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY) annotated method.

Note that the fragment's viewLifecycleOwner is only available between onCreateView and onDestroyView lifecycle methods.

回答2:

Just a supplement to Basim Alamuddin's answer：

As you can see in the resource codes, @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY) is also called when you add an observer to viewLifecycleOwner: viewLifecycleOwner.lifecycle.addObserver(this)

// androidx.fragment.app.Fragment

void performDestroyView() {
    if (mView != null) {
        mViewLifecycleOwner.handleLifecycleEvent(Lifecycle.Event.ON_DESTROY);
    }
    onDestroyView();

void performDestroy() {
    mLifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_DESTROY);
    onDestroy();

回答3:

Well, according to this, literally onDestroyView will be called after onStop. So, If you need the logic to run before onDestroyView or detecting it, i think it's is best to call it or detect in the fragment's onStop() method. In your case, i think you need to implement Lifecycle.Event.ON_STOP & Lifecycle.Event.ON_START for onActivityCreated.

Hope it helps you.

回答4:

Fragment Life Cycle

onCreateView()

Called to create the view hierarchy associated with the fragment.

onDestroyView()

Called when the view hierarchy associated with the fragment is being removed.

来源：https://stackoverflow.com/questions/47091794/fragment-lifecycle-events-in-lifecycleaware-fragment