dependencies {
    def lifecycle_version = "2.5.0-alpha01"
    def arch_version = "2.1.0"
 
    implementation "androidx.lifecycle:lifecycle-viewmodel:$lifecycle_version"
  
    implementation "androidx.lifecycle:lifecycle-livedata:$lifecycle_version"
 
    implementation "androidx.lifecycle:lifecycle-runtime:$lifecycle_version"
 
    //非java8使用
    annotationProcessor "androidx.lifecycle:lifecycle-compiler:$lifecycle_version" 
    //java8使用
    implementation "androidx.lifecycle:lifecycle-common-java8:$lifecycle_version"  
}

public class BaseJsApi implements LifecycleObserver {
 
  
    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    void create() {
        onCreate();
    }
 
    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    void destroy() {
        onDestroy();
    }
 
 
    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    void resume() {
        onResume();
    }
 
    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    void pause() {
        onPause();
    }
 
    ……………………………………
 
  }

 getLifecycle().addObserver(getJsBridge());

public interface LifecycleObserver {
 
}
 
public interface LifecycleOwner {
  @NonNull
  Lifecycle getLifecycle();
}

public class LifecycleRegistry extends Lifecycle {
  
 
}
 
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();
 
    public enum Event {
       
        ON_CREATE,
       
        ON_START,
        
        ON_RESUME,
        
        ON_PAUSE,
        
        ON_STOP,
        
        ON_DESTROY,
       
        ON_ANY;
        …………………………………………
      }
      ………………………………
}

@Override
public void addObserver(@NonNull LifecycleObserver observer) {
    //檢查是否在主線程
    enforceMainThreadIfNeeded("addObserver");
    //設(shè)置狀態(tài)值
    State initialState = mState == DESTROYED ? DESTROYED : INITIALIZED;
    //將觀察者和初始化的值封裝到ObserverWithState中
    ObserverWithState statefulObserver = new ObserverWithState(observer, initialState);
    //以觀察者為key，statefulObserver為value放到hashMap集合中
    ObserverWithState previous = mObserverMap.putIfAbsent(observer, statefulObserver);
    //不為null表示之前已經(jīng)放進(jìn)去了，否則沒(méi)放進(jìn)去，放進(jìn)去了就添加結(jié)束
    if (previous != null) {
        return;
    }
    //獲取被觀察者對(duì)象，即Activity，如果被銷毀了，則結(jié)束
    LifecycleOwner lifecycleOwner = mLifecycleOwner.get();
    if (lifecycleOwner == null) {
        // it is null we should be destroyed. Fallback quickly
        return;
    }
 
    //mAddingObserverCounter 表示正在添加的觀察者的數(shù)量，
    //開始添加新的observe之前，對(duì)該變量進(jìn)行++操作，添加完成后，進(jìn)行--操作。
    //mHandlingEvent表示是否正在處理
    boolean isReentrance = mAddingObserverCounter != 0 || mHandlingEvent;
    //計(jì)算狀態(tài)，進(jìn)行while循環(huán)
    State targetState = calculateTargetState(observer);
    mAddingObserverCounter++;
    //新添加的LifecycleObserver ，會(huì)不斷更新自己的生命周期到指定的targetState
    while ((statefulObserver.mState.compareTo(targetState) < 0
            && mObserverMap.contains(observer))) {
        //添加狀態(tài)到list，計(jì)算當(dāng)前狀態(tài)，用于計(jì)算狀態(tài)calculateTargetState
        pushParentState(statefulObserver.mState);
        //
        final Event event = Event.upFrom(statefulObserver.mState);
        if (event == null) {
            throw new IllegalStateException("no event up from " + statefulObserver.mState);
        }
        //生命周期分發(fā)：分發(fā)到mLifecycleObserver里面
        statefulObserver.dispatchEvent(lifecycleOwner, event);
        //移除狀態(tài)到list
        popParentState();
        // mState / subling may have been changed recalculate
        //重新計(jì)算狀態(tài)
        targetState = calculateTargetState(observer);
    }
    //沒(méi)有事件正在處理，或者是添加了observe,就需要重新同步一次狀態(tài),下面詳細(xì)介紹
    if (!isReentrance) {
        // we do sync only on the top level.
        sync();
    }
    mAddingObserverCounter--;
}

//計(jì)算狀態(tài)規(guī)則
private State calculateTargetState(LifecycleObserver observer) {
    //在map中獲取到當(dāng)前observer的前一個(gè)observer
    Map.Entry<LifecycleObserver, ObserverWithState> previous = mObserverMap.ceil(observer);
    //前一個(gè)observer的state
    State siblingState = previous != null ? previous.getValue().mState : null;
    //如果是嵌套添加observer，獲取父級(jí)observer的狀態(tài)
    State parentState = !mParentStates.isEmpty() ? mParentStates.get(mParentStates.size() - 1)
            : null;
    //獲取最小狀態(tài)，DESTROYED < INITIALIZED < CREATED < STARTED < RESUMED
    return min(min(mState, siblingState), parentState);
}

public static void injectIfNeededIn(Activity activity) {
    //當(dāng)API>=29注冊(cè)registerIn綁定生命周期
    if (Build.VERSION.SDK_INT >= 29) {
        // On API 29+, we can register for the correct Lifecycle callbacks directly
        LifecycleCallbacks.registerIn(activity);
    }
    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 onStart() {
    super.onStart();
    dispatchStart(mProcessListener);
    dispatch(Lifecycle.Event.ON_START);
}

private void dispatch(@NonNull Lifecycle.Event event) {
    //當(dāng)API<29分發(fā)dispatch綁定生命周期
    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);
    }
}

static void dispatch(@NonNull Activity activity, @NonNull Lifecycle.Event event) {
    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);
        }
    }
}

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.");
    }
    //沒(méi)有同步過(guò)，則同步
    while (!isSynced()) {
        mNewEventOccurred = false;
        // no need to check eldest for nullability, because isSynced does it for us.
        if (mState.compareTo(mObserverMap.eldest().getValue().mState) < 0) {
            //如果ObserverWithState的state小于當(dāng)前state，那么就調(diào)用forwardPass方法，
            backwardPass(lifecycleOwner);
        }
        Map.Entry<LifecycleObserver, ObserverWithState> newest = mObserverMap.newest();
        if (!mNewEventOccurred && newest != null
                && mState.compareTo(newest.getValue().mState) > 0) {
            //如果大于當(dāng)前state，那么就調(diào)用backwardPass方法。
            forwardPass(lifecycleOwner);
        }
    }
    mNewEventOccurred = false;
}

static class ObserverWithState {
    State mState;
    LifecycleEventObserver mLifecycleObserver;
 
    ObserverWithState(LifecycleObserver observer, State initialState) {
        mLifecycleObserver = Lifecycling.lifecycleEventObserver(observer);
        mState = initialState;
    }
 
    void dispatchEvent(LifecycleOwner owner, Event event) {
        State newState = event.getTargetState();
        mState = min(mState, newState);
        mLifecycleObserver.onStateChanged(owner, event);
        mState = newState;
    }
}

static LifecycleEventObserver lifecycleEventObserver(Object object) {
    boolean isLifecycleEventObserver = object instanceof LifecycleEventObserver;
    boolean isFullLifecycleObserver = object instanceof FullLifecycleObserver;
    if (isLifecycleEventObserver && isFullLifecycleObserver) {
        return new FullLifecycleObserverAdapter((FullLifecycleObserver) object,
                (LifecycleEventObserver) object);
    }
    if (isFullLifecycleObserver) {
        return new FullLifecycleObserverAdapter((FullLifecycleObserver) object, null);
    }
 
    if (isLifecycleEventObserver) {
        return (LifecycleEventObserver) object;
    }
    //通過(guò)反射，找到Lifecycle 自動(dòng)生成的類
    final Class<?> klass = object.getClass();
    int type = getObserverConstructorType(klass);
    if (type == GENERATED_CALLBACK) {
        List<Constructor<? extends GeneratedAdapter>> constructors =
                sClassToAdapters.get(klass);
        if (constructors.size() == 1) {
            GeneratedAdapter generatedAdapter = createGeneratedAdapter(
                    constructors.get(0), object);
            最終使用生成的Adapter，創(chuàng)建SingleGeneratedAdapterObserver
            return new SingleGeneratedAdapterObserver(generatedAdapter);
        }
        GeneratedAdapter[] adapters = new GeneratedAdapter[constructors.size()];
        for (int i = 0; i < constructors.size(); i++) {
            adapters[i] = createGeneratedAdapter(constructors.get(i), object);
        }
        return new CompositeGeneratedAdaptersObserver(adapters);
    }
    return new ReflectiveGenericLifecycleObserver(object);
}

class SingleGeneratedAdapterObserver implements LifecycleEventObserver {
 
    private final GeneratedAdapter mGeneratedAdapter;
 
    SingleGeneratedAdapterObserver(GeneratedAdapter generatedAdapter) {
        mGeneratedAdapter = generatedAdapter;
    }
 
    @Override
    public void onStateChanged(@NonNull LifecycleOwner source, @NonNull Lifecycle.Event event) {
        mGeneratedAdapter.callMethods(source, event, false, null);
        mGeneratedAdapter.callMethods(source, event, true, null);
    }
}