目录
一、Lifecycle使用
二、LifecycleObserver注册
三、OnLifecycleEvent注解解析
四、生命周期监听与回调
五、总结
一、Lifecycle使用
1.1 Lifecycle对生命周期的监听
使用LifecycleObserver监听生命周期需要被监听对象实现LifecycleOwner，Activity实现了这个接口，直接getLifecycle.addObserver()将观察者和被观察者关联。这样在Activity创建调用生命周期时就可以通过LifecycleObserver感知到Activity的生命周期
class LifecycleTestActivity : AppCompatActivity(){
···
private val mLifecycleMvp = LifeCycleMvp()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_lifecycle_test)
lifecycle.addObserver(mLifecycleMvp)
}
}
class LifeCycleMvp :LifecycleObserver{
@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
fun onCreate(){
Log.i("yyy","oncreate")
}
@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
fun onDestroy(){
Log.i("yyy","onDestroy")
}
}
二、LifecycleObserver注册
lifecycle.addObserver(mLifecycleMvp) 添加对生命周期的监听，这个lifecycle是一个LifecycleRegistry类型
ComponentActivity.java
private final LifecycleRegistry mLifecycleRegistry = new LifecycleRegistry(this);
public Lifecycle getLifecycle() {
return mLifecycleRegistry;
}
LifecycleRegistry在创建时将当前的Activity作为参数传入，LifecycleRegistry使用弱引用缓存
LifecycleRegistry.java
public LifecycleRegistry(@NonNull LifecycleOwner provider) {
mLifecycleOwner = new WeakReference<>(provider);
mState = INITIALIZED;
}
添加观察者到观察列表中
LifecycleRegistry.java
public void addObserver(@NonNull LifecycleObserver observer) {
State initialState = mState == DESTROYED ? DESTROYED : INITIALIZED;
//创建观察状态类用于回调
ObserverWithState statefulObserver = new ObserverWithState(observer, initialState);
ObserverWithState previous = mObserverMap.putIfAbsent(observer, statefulObserver);
//如果已经存在了直接返回
if (previous != null) {
return;
}
//当前的Activity已经被回收
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++;
//如果当前状态大于监听状态，通知观察者
while ((statefulObserver.mState.compareTo(targetState) < 0
&& mObserverMap.contains(observer))) {
pushParentState(statefulObserver.mState);
//分发通知
statefulObserver.dispatchEvent(lifecycleOwner, upEvent(statefulObserver.mState));
popParentState();
// mState / subling may have been changed recalculate
targetState = calculateTargetState(observer);
}
if (!isReentrance) {
// we do sync only on the top level.
sync();
}
mAddingObserverCounter--;
}
三、OnLifecycleEvent注解解析
3.1 调用解析OnLifecycleEvent
在lifecycle.addObserver(mLifecycleMvp)的时候，会创建一个ObserverWithState的类用于解析OnLifecycleEvent和实现生命周期的回调
ObserverWithState.java
static class ObserverWithState {
State mState;
LifecycleEventObserver mLifecycleObserver;
ObserverWithState(LifecycleObserver observer, State initialState) {
//在初始化的时候使用Lifecycling.解析注解lifecycleEventObserver
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;
}
}
Lifecycling.lifecycleEventObserver(observer);用于解析OnLifecycleEvent的注解
Lifecycling.java
static LifecycleEventObserver lifecycleEventObserver(Object object) {
//如果是LifecycleEventObserver或者FullLifecycleObserver类型直接返回FullLifecycleObserverAdapter，
//我们也可以实现LifecycleEventObserver用于监听整个生命周期
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);
}
//只是LifecycleEventObserver也是直接返回
if (isLifecycleEventObserver) {
return (LifecycleEventObserver) object;
}
final Class<?> klass = object.getClass();
//开始解析
int type = getObserverConstructorType(klass);
//如果是GeneratedAdapter 返回对应的Adapter
if (type == GENERATED_CALLBACK) {
List<Constructor<? extends GeneratedAdapter>> constructors =
sClassToAdapters.get(klass);
if (constructors.size() == 1) {
GeneratedAdapter generatedAdapter = createGeneratedAdapter(
constructors.get(0), object);
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);
}
//如果是反射类型 开始反射
return new ReflectiveGenericLifecycleObserver(object);
}
3.2 解析OnLifecycleEvent注解
int type = getObserverConstructorType(klass); kclass是入进来的ifecycleObserver
Lifecycling.java
private static int getObserverConstructorType(Class<?> klass) {
//如果缓存直接返回类型
Integer callbackCache = sCallbackCache.get(klass);
if (callbackCache != null) {
return callbackCache;
}
//解析观察者类型
int type = resolveObserverCallbackType(klass);
sCallbackCache.put(klass, type);
return type;
}
Lifecycling.java
private static int resolveObserverCallbackType(Class<?> klass) {
// anonymous class bug:35073837
if (klass.getCanonicalName() == null) {
return REFLECTIVE_CALLBACK;
}
//反射创建生成Adapter减少反射性能消耗
Constructor<? extends GeneratedAdapter> constructor = generatedConstructor(klass);
if (constructor != null) {
sClassToAdapters.put(klass, Collections
.<Constructor<? extends GeneratedAdapter>>singletonList(constructor));
return GENERATED_CALLBACK;
}
//包含传入的类OnLifecycleEvent注解方法
boolean hasLifecycleMethods = ClassesInfoCache.sInstance.hasLifecycleMethods(klass);
if (hasLifecycleMethods) {
return REFLECTIVE_CALLBACK;
}
Class<?> superclass = klass.getSuperclass();
List<Constructor<? extends GeneratedAdapter>> adapterConstructors = null;
if (isLifecycleParent(superclass)) {
if (getObserverConstructorType(superclass) == REFLECTIVE_CALLBACK) {
return REFLECTIVE_CALLBACK;
}
adapterConstructors = new ArrayList<>(sClassToAdapters.get(superclass));
}
for (Class<?> intrface : klass.getInterfaces()) {
if (!isLifecycleParent(intrface)) {
continue;
}
if (getObserverConstructorType(intrface) == REFLECTIVE_CALLBACK) {
return REFLECTIVE_CALLBACK;
}
if (adapterConstructors == null) {
adapterConstructors = new ArrayList<>();
}
adapterConstructors.addAll(sClassToAdapters.get(intrface));
}
if (adapterConstructors != null) {
sClassToAdapters.put(klass, adapterConstructors);
return GENERATED_CALLBACK;
}
return REFLECTIVE_CALLBACK;
}
3.2.1 反射创建GeneratedAdapter
generatedConstructor(klass);会反射创建报名+ "_LifecycleAdapter"的类
Lifecycling.java
@Nullable
private static Constructor<? extends GeneratedAdapter> generatedConstructor(Class<?> klass) {
try {
//获取包名
Package aPackage = klass.getPackage();
String name = klass.getCanonicalName();
final String fullPackage = aPackage != null ? aPackage.getName() : "";
final String adapterName = getAdapterName(fullPackage.isEmpty() ? name :
name.substring(fullPackage.length() + 1));
//通过类名获取class
@SuppressWarnings("unchecked") final Class<? extends GeneratedAdapter> aClass =
(Class<? extends GeneratedAdapter>) Class.forName(
fullPackage.isEmpty() ? adapterName : fullPackage + "." + adapterName);
Constructor<? extends GeneratedAdapter> constructor =
aClass.getDeclaredConstructor(klass);
if (!constructor.isAccessible()) {
constructor.setAccessible(true);
}
//返回反射处理的构造方法
return constructor;
} catch (ClassNotFoundException e) {
return null;
} catch (NoSuchMethodException e) {
// this should not happen
throw new RuntimeException(e);
}
}
3.2.2 检测传入的类OnLifecycleEvent注解方法
ClassesInfoCache.sInstance.hasLifecycleMethods(klass);检测是否含有注解，并创建和缓存callbackinfo
ClassesInfoCache.java
boolean hasLifecycleMethods(Class<?> klass) {
//如果有缓存直接返回缓存
Boolean hasLifecycleMethods = mHasLifecycleMethods.get(klass);
if (hasLifecycleMethods != null) {
return hasLifecycleMethods;
}
//获取传入类的方法
Method[] methods = getDeclaredMethods(klass);
//编列方法
for (Method method : methods) {
//获取OnLifecycleEvent注解
OnLifecycleEvent annotation = method.getAnnotation(OnLifecycleEvent.class);
if (annotation != null) {
····
//创建当生命周期被调用后需要调用的信息
createInfo(klass, methods);
return true;
}
}
mHasLifecycleMethods.put(klass, false);
return false;
}
3.2.2 解析并缓存当生命周期被调用后需要调用的信息
ClassesInfoCache.java
private CallbackInfo createInfo(Class<?> klass, @Nullable Method[] declaredMethods) {
//获取父类
Class<?> superclass = klass.getSuperclass();
//创建方法引用和Lifecycle.Event
Map<MethodReference, Lifecycle.Event> handlerToEvent = new HashMap<>();
if (superclass != null) {
//父类不为空获取callbackinfo信息
CallbackInfo superInfo = getInfo(superclass);
if (superInfo != null) {
handlerToEvent.putAll(superInfo.mHandlerToEvent);
}
}
//获取父接口
Class<?>[] interfaces = klass.getInterfaces();
for (Class<?> intrfc : interfaces) {
for (Map.Entry<MethodReference, Lifecycle.Event> entry : getInfo(
intrfc).mHandlerToEvent.entrySet()) {
//父接口不为空获取callbackinfo信息
verifyAndPutHandler(handlerToEvent, entry.getKey(), entry.getValue(), klass);
}
}
//获取当前类方法
Method[] methods = declaredMethods != null ? declaredMethods : getDeclaredMethods(klass);
boolean hasLifecycleMethods = false;
//遍历当前类方法并解析注解，存入缓存
for (Method method : methods) {
OnLifecycleEvent annotation = method.getAnnotation(OnLifecycleEvent.class);
if (annotation == null) {
continue;
}
hasLifecycleMethods = true;
Class<?>[] params = method.getParameterTypes();
int callType = CALL_TYPE_NO_ARG;
if (params.length > 0) {
callType = CALL_TYPE_PROVIDER;
if (!params[0].isAssignableFrom(LifecycleOwner.class)) {
throw new IllegalArgumentException(
"invalid parameter type. Must be one and instanceof LifecycleOwner");
}
}
Lifecycle.Event event = annotation.value();
if (params.length > 1) {
callType = CALL_TYPE_PROVIDER_WITH_EVENT;
···
}
if (params.length > 2) {
····
}
MethodReference methodReference = new MethodReference(callType, method);
verifyAndPutHandler(handlerToEvent, methodReference, event, klass);
}
//创建callbackinfo
CallbackInfo info = new CallbackInfo(handlerToEvent);
mCallbackMap.put(klass, info);
mHasLifecycleMethods.put(klass, hasLifecycleMethods);
return info;
}
3.2.3 将反射信息包装成ReflectiveGenericLifecycleObserver
获取观察者类型后创建了ReflectiveGenericLifecycleObserver，他封装了调用信息，和生命周期触发时的调用方法
Lifecycling.java
static LifecycleEventObserver lifecycleEventObserver(Object object) {
···
int type = getObserverConstructorType(klass);
···
return new ReflectiveGenericLifecycleObserver(object);
}
ReflectiveGenericLifecycleObserver.java
class ReflectiveGenericLifecycleObserver implements LifecycleEventObserver {
private final Object mWrapped;
private final CallbackInfo mInfo;
ReflectiveGenericLifecycleObserver(Object wrapped) {
//当前传入的对象
mWrapped = wrapped;
//回去反射的信息
mInfo = ClassesInfoCache.sInstance.getInfo(mWrapped.getClass());
}
@Override
public void onStateChanged(@NonNull LifecycleOwner source, @NonNull Event event) {
//生命周期回调
mInfo.invokeCallbacks(source, event, mWrapped);
}
}
四、生命周期监听与回调
4.1 生命周期的监听
被观察的Activity在创建的时候调用了ReportFragment.injectIfNeededIn(this)实现了一个隐藏的Fragment用于监听Activity的生命周期
ComponentActivity.java
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mSavedStateRegistryController.performRestore(savedInstanceState);
ReportFragment.injectIfNeededIn(this);
if (mContentLayoutId != 0) {
setContentView(mContentLayoutId);
}
}
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
//获取fragmentmanager，添加自己到Activity中
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();
}
}
4.2 生命周期的回调
当触发Activity生命周期时，会调用ReportFragment的生命周期
ReportFragment.java
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
dispatchCreate(mProcessListener);
//调用回调
dispatch(Lifecycle.Event.ON_CREATE);
}
ReportFragment.java
private void dispatch(Lifecycle.Event event) {
Activity activity = getActivity();
if (activity instanceof LifecycleRegistryOwner) {
((LifecycleRegistryOwner) activity).getLifecycle().handleLifecycleEvent(event);
return;
}
if (activity instanceof LifecycleOwner) {
//如果是LifecycleOwner类型，获取getLifecycle，强转LifecycleRegistry并调用handleLifecycleEvent方法
Lifecycle lifecycle = ((LifecycleOwner) activity).getLifecycle();
if (lifecycle instanceof LifecycleRegistry) {
((LifecycleRegistry) lifecycle).handleLifecycleEvent(event);
}
}
}
LifecycleRegistry.java
public void handleLifecycleEvent(@NonNull Lifecycle.Event event) {
//获取状态
State next = getStateAfter(event);
//分发状态
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;
//开始分发
sync();
mHandlingEvent = false;
}
LifecycleRegistry.java
private void sync() {
LifecycleOwner lifecycleOwner = mLifecycleOwner.get();
···
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) {
//触发回调
backwardPass(lifecycleOwner);
}
Entry<LifecycleObserver, ObserverWithState> newest = mObserverMap.newest();
if (!mNewEventOccurred && newest != null
&& mState.compareTo(newest.getValue().mState) > 0) {
//触发回调
forwardPass(lifecycleOwner);
}
}
mNewEventOccurred = false;
}
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);
//调用回调
observer.dispatchEvent(lifecycleOwner, upEvent(observer.mState));
popParentState();
}
}
}
private void backwardPass(LifecycleOwner lifecycleOwner) {
Iterator<Entry<LifecycleObserver, ObserverWithState>> descendingIterator =
mObserverMap.descendingIterator();
while (descendingIterator.hasNext() && !mNewEventOccurred) {
Entry<LifecycleObserver, ObserverWithState> entry = descendingIterator.next();
ObserverWithState observer = entry.getValue();
while ((observer.mState.compareTo(mState) > 0 && !mNewEventOccurred
&& mObserverMap.contains(entry.getKey()))) {
Event event = downEvent(observer.mState);
pushParentState(getStateAfter(event));
//调用回调
observer.dispatchEvent(lifecycleOwner, event);
popParentState();
}
}
}
触发ObserverWithState的dispatchEvent()方法，调用mLifecycleObserver.onStateChanged(owner, event);如果是反射调用的是ReflectiveGenericLifecycleObserver的onStateChanged
ObserverWithState.java
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 = getStateAfter(event);
mState = min(mState, newState);
mLifecycleObserver.onStateChanged(owner, event);
mState = newState;
}
}
ReflectiveGenericLifecycleObserver.java
@Override
public void onStateChanged(LifecycleOwner source, Event event) {
mInfo.invokeCallbacks(source, event, mWrapped);
}
ClassesInfoCache.CallbackInfo.java
void invokeCallbacks(LifecycleOwner source, Lifecycle.Event event, Object target) {
invokeMethodsForEvent(mEventToHandlers.get(event), source, event, target);
invokeMethodsForEvent(mEventToHandlers.get(Lifecycle.Event.ON_ANY), source, event,
target);
}
ClassesInfoCache.java
private static void invokeMethodsForEvent(List<MethodReference> handlers,
LifecycleOwner source, Lifecycle.Event event, Object mWrapped) {
if (handlers != null) {
for (int i = handlers.size() - 1; i >= 0; i--) {
handlers.get(i).invokeCallback(source, event, mWrapped);
}
}
}
ClassesInfoCache.MethodReference.java
void invokeCallback(LifecycleOwner source, Lifecycle.Event event, Object target) {
//noinspection TryWithIdenticalCatches
try {
//触发最终的调用
switch (mCallType) {
case CALL_TYPE_NO_ARG:
mMethod.invoke(target);
break;
case CALL_TYPE_PROVIDER:
mMethod.invoke(target, source);
break;
case CALL_TYPE_PROVIDER_WITH_EVENT:
mMethod.invoke(target, source, event);
break;
}
} catch (InvocationTargetException e) {
throw new RuntimeException("Failed to call observer method", e.getCause());
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}
五、总结
1、监听Activity生命周期可以实现LifecycleObserver，使用@OnLifecycleEvent注解修饰需要被特定生命周期要调用的方法，也可是实现LifecycleEventObserver监听Activity生命周期
2、观察者被包装成ObserverWithState添加到map中
3、实现的是LifecycleEventObserver直接返回，是LifecycleObserver就解析注解
4、如果有GeneratedAdapter就直接返回，如果没有解析注解
5、注册ReportFragment监听Activity生命周期
6、调用ReportFragment生命周期触发反射缓存的method方法
