jetpack-Lifecycle

ComponentActivity 实现 LifecycleOwner接口，而AppcompatActivity继承CompomentActivity

public interface LifecycleOwner {
    @NonNull
    Lifecycle getLifecycle();
}
public class ComponentActivity extends Activity
        implements LifecycleOwner, KeyEventDispatcher.Component {
            
            
}

LifeCycle

public abstract class Lifecycle {
    public abstract void addObserver(@NonNull LifecycleObserver observer);
    public abstract void removeObserver(@NonNull LifecycleObserver observer);
    
}
public class LifecycleRegistry extends Lifecycle {
    @Override
public void addObserver(@NonNull LifecycleObserver observer) {
    //略
    while ((statefulObserver.mState.compareTo(targetState) < 0
            && mObserverMap.contains(observer))) {
        pushParentState(statefulObserver.mState);
        statefulObserver.dispatchEvent(lifecycleOwner, upEvent(statefulObserver.mState));
        popParentState();
        // mState / subling may have been changed recalculate
        targetState = calculateTargetState(observer);
    }
    //略

}

}

如果通过按钮点击添加注册，它会从初始state 到onResumed一直调过来

生命周期怎么监听？

通过添加一个空ReportFragment

ComponentActivity.java

@Override
@SuppressWarnings("RestrictedApi")
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ReportFragment.injectIfNeededIn(this);
}

ReportFragment.java

public static void injectIfNeededIn(Activity activity) {
    // ProcessLifecycleOwner should always correctly work and some activities may not extend
    // FragmentActivity from support lib, so we use framework fragments for activities
    android.app.FragmentManager manager = activity.getFragmentManager();
    if (manager.findFragmentByTag(REPORT_FRAGMENT_TAG) == null) {
        manager.beginTransaction().add(new ReportFragment(), REPORT_FRAGMENT_TAG).commit();
        // Hopefully, we are the first to make a transaction.
        manager.executePendingTransactions();
    }
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    dispatchCreate(mProcessListener);
    dispatch(Lifecycle.Event.ON_CREATE);
}

@Override
public void onStart() {
    super.onStart();
    dispatchStart(mProcessListener);
    dispatch(Lifecycle.Event.ON_START);
}

@Override
public void onResume() {
    super.onResume();
    dispatchResume(mProcessListener);
    dispatch(Lifecycle.Event.ON_RESUME);
}

ReportFragment的分发

private void dispatch(Lifecycle.Event event) {
    Activity activity = getActivity();
    if (activity instanceof LifecycleRegistryOwner) {
        ((LifecycleRegistryOwner) activity).getLifecycle().handleLifecycleEvent(event);
        return;
    }

    if (activity instanceof LifecycleOwner) {
        Lifecycle lifecycle = ((LifecycleOwner) activity).getLifecycle();
        if (lifecycle instanceof LifecycleRegistry) {
            ((LifecycleRegistry) lifecycle).handleLifecycleEvent(event);
        }
    }
}