- State是如何与Activity/Fragment的生命周期绑定的？
在Activity中添加一个ReportFragment(如果你的Activity继承AppCompatActivity，会在父类的onCreate()中添加ReportFragment，否则由LifecycleDispatcher添加)，在ReportFragment生命周期函数中调用LifecycleRegistry.handleLifecycleEvent()方法改变State。
- Event事件是如何分发到LifecycleObserver的？
LifecycleRegistry在收到handleLifecycleEvent()后，内部调用moveToState()方法，改变State值，每一次State值改变，都会调用LifecycleObserver.onStateChanged()方法将Event分发到LifecycleObserver
使用ReportFragment实现无侵入
//ComponentActivity.java
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// 注入Fragment
ReportFragment.injectIfNeededIn(this);
}
ReportFragment中
- Android10以下在ReportFragment生命周期中分发事件
- Android10以上ReportFragment注册ActivityLifecycleCallbacks，监听生命周期变化分发给
LifecycleRegistry.handleLifecycleEvent
private void dispatch(@NonNull Lifecycle.Event event) {
if (Build.VERSION.SDK_INT < 29) {
// Only dispatch events from ReportFragment on API levels prior
// to API 29. On API 29+, this is handled by the ActivityLifecycleCallbacks
// added in ReportFragment.injectIfNeededIn
dispatch(getActivity(), event);
}
}
有的页面不继承自AppCompatActivity，则通过ContentProvider，进程启动的时候自动注册
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="androidx.lifecycle.process" >
<application>
<provider
android:name="androidx.lifecycle.ProcessLifecycleOwnerInitializer"
android:authorities="${applicationId}.lifecycle-process"
android:exported="false"
android:multiprocess="true" />
</application>
</manifest>
public class ProcessLifecycleOwnerInitializer extends ContentProvider {
@Override
public boolean onCreate() {
//自动注册
LifecycleDispatcher.init(getContext());
ProcessLifecycleOwner.init(getContext());
return true;
}
}
class LifecycleDispatcher {
private static AtomicBoolean sInitialized = new AtomicBoolean(false);
static void init(Context context) {
if (sInitialized.getAndSet(true)) {
return;
}
//Application监听Activity情况
((Application) context.getApplicationContext()).registerActivityLifecycleCallbacks(new DispatcherActivityCallback());
}
static class DispatcherActivityCallback extends EmptyActivityLifecycleCallbacks {
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
//Activity创建后自动注册
ReportFragment.injectIfNeededIn(activity);
}
@Override
public void onActivityStopped(Activity activity) {
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
}
}
}
Lifecycle：不包含实现
public abstract class Lifecycle {
@MainThread
public abstract void addObserver(@NonNull LifecycleObserver observer);
@MainThread
public abstract void removeObserver(@NonNull LifecycleObserver observer);
@MainThread
@NonNull
public abstract State getCurrentState();
@SuppressWarnings("WeakerAccess")
public enum Event {
...
}
public enum State {
...
}
}
LifecycleRegistry：处理生命周期事件，转移状态，通知观察者
public class LifecycleRegistry extends Lifecycle {
// 保存Observer Map，封装ObserverWithState
private FastSafeIterableMap<LifecycleObserver, ObserverWithState> mObserverMap =
new FastSafeIterableMap<>();
// 保存生命周期状态
private State mState;
// 弱引用持有Activity
private final WeakReference<LifecycleOwner> mLifecycleOwner;
private int mAddingObserverCounter = 0;
private boolean mHandlingEvent = false;
private boolean mNewEventOccurred = false;
private ArrayList<State> mParentStates = new ArrayList<>();
public LifecycleRegistry(@NonNull LifecycleOwner provider) {
mLifecycleOwner = new WeakReference<>(provider);
mState = INITIALIZED;
}
@MainThread
public void setCurrentState(@NonNull State state) {
moveToState(state);
}
public void handleLifecycleEvent(@NonNull Lifecycle.Event event) {
State next = getStateAfter(event);
moveToState(next);
}
private void moveToState(State next) {
if (mState == next) {
return;
}
mState = next;
if (mHandlingEvent || mAddingObserverCounter != 0) {
mNewEventOccurred = true;
// we will figure out what to do on upper level.
return;
}
mHandlingEvent = true;
sync();
mHandlingEvent = false;
}
private boolean isSynced() {
if (mObserverMap.size() == 0) {
return true;
}
State eldestObserverState = mObserverMap.eldest().getValue().mState;
State newestObserverState = mObserverMap.newest().getValue().mState;
return eldestObserverState == newestObserverState && mState == newestObserverState;
}
private State calculateTargetState(LifecycleObserver observer) {
Entry<LifecycleObserver, ObserverWithState> previous = mObserverMap.ceil(observer);
State siblingState = previous != null ? previous.getValue().mState : null;
State parentState = !mParentStates.isEmpty() ? mParentStates.get(mParentStates.size() - 1)
: null;
return min(min(mState, siblingState), parentState);
}
@Override
public void addObserver(@NonNull LifecycleObserver observer) {
State initialState = mState == DESTROYED ? DESTROYED : INITIALIZED;
ObserverWithState statefulObserver = new ObserverWithState(observer, initialState);
ObserverWithState previous = mObserverMap.putIfAbsent(observer, statefulObserver);
if (previous != null) {
return;
}
LifecycleOwner lifecycleOwner = mLifecycleOwner.get();
if (lifecycleOwner == null) {
// it is null we should be destroyed. Fallback quickly
return;
}
boolean isReentrance = mAddingObserverCounter != 0 || mHandlingEvent;
State targetState = calculateTargetState(observer);
mAddingObserverCounter++;
while ((statefulObserver.mState.compareTo(targetState) < 0
&& mObserverMap.contains(observer))) {
pushParentState(statefulObserver.mState);
statefulObserver.dispatchEvent(lifecycleOwner, upEvent(statefulObserver.mState));
popParentState();
targetState = calculateTargetState(observer);
}
if (!isReentrance) {
sync();
}
mAddingObserverCounter--;
}
@Override
public void removeObserver(@NonNull LifecycleObserver observer) {
mObserverMap.remove(observer);
}
@SuppressWarnings("WeakerAccess")
public int getObserverCount() {
return mObserverMap.size();
}
@NonNull
@Override
public State getCurrentState() {
return mState;
}
private void forwardPass(LifecycleOwner lifecycleOwner) {
Iterator<Entry<LifecycleObserver, ObserverWithState>> ascendingIterator =
mObserverMap.iteratorWithAdditions();
while (ascendingIterator.hasNext() && !mNewEventOccurred) {
Entry<LifecycleObserver, ObserverWithState> entry = ascendingIterator.next();
ObserverWithState observer = entry.getValue();
while ((observer.mState.compareTo(mState) < 0 && !mNewEventOccurred
&& mObserverMap.contains(entry.getKey()))) {
pushParentState(observer.mState);
//downEvent、upEvent计算下一个状态
observer.dispatchEvent(lifecycleOwner, upEvent(observer.mState));
popParentState();
}
}
}
private void sync() {
LifecycleOwner lifecycleOwner = mLifecycleOwner.get();
if (lifecycleOwner == null) {
throw new IllegalStateException("LifecycleOwner of this LifecycleRegistry is already"
+ "garbage collected. It is too late to change lifecycle state.");
}
while (!isSynced()) {
mNewEventOccurred = false;
if (mState.compareTo(mObserverMap.eldest().getValue().mState) < 0) {
backwardPass(lifecycleOwner);
}
Entry<LifecycleObserver, ObserverWithState> newest = mObserverMap.newest();
if (!mNewEventOccurred && newest != null
&& mState.compareTo(newest.getValue().mState) > 0) {
forwardPass(lifecycleOwner);
}
}
mNewEventOccurred = false;
}
static class ObserverWithState {
State mState;
LifecycleEventObserver mLifecycleObserver;
ObserverWithState(LifecycleObserver observer, State initialState) {
// 封装ObserverWithState
mLifecycleObserver = Lifecycling.lifecycleEventObserver(observer);
mState = initialState;
}
void dispatchEvent(LifecycleOwner owner, Event event) {
State newState = getStateAfter(event);
mState = min(mState, newState);
mLifecycleObserver.onStateChanged(owner, event);
mState = newState;
}
}
}
static LifecycleEventObserver lifecycleEventObserver(Object object) {
//统一回调onStateChanged
boolean isLifecycleEventObserver = object instanceof LifecycleEventObserver;
//回调所有生命周期，onStateChanged中判断了Event。不过这个类是私有的，开发者无法使用
boolean isFullLifecycleObserver = object instanceof FullLifecycleObserver;
if (isLifecycleEventObserver && isFullLifecycleObserver) {
return new FullLifecycleObserverAdapter((FullLifecycleObserver) object,
(LifecycleEventObserver) object);
}
if (isFullLifecycleObserver) {
// 为null表示不回调onStateChanged
return new FullLifecycleObserverAdapter((FullLifecycleObserver) object, null);
}
if (isLifecycleEventObserver) {
return (LifecycleEventObserver) object;
}
...
}