Android Lifecycle源码解析
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参考技术ALifecycle是生命周期的意思。它是Jetpack中的一个 生命周期感知型组件 ，可执行操作来感知响应另一个组件（如 Activity 和 Fragment）的生命周期状态的变化。
1.第一步添加依赖
2.实现LifecycleObserver接口以及添加注解
3.在Activity中或者Fragment中调用lifecycle.addObserver方法,把LifecycleObserver传入进去就可以
使用是不是很简单,在MytViewModelLifecycle里面就可以监听到Activity中或者Fragment生命周期了
1.首先分析lifecycle怎么来的
lifecycle调用的是ComponentActivity的getLifecycle方法,返回了一个mLifecycleRegistry
那么我们就从ComponentActivity入手会实现了它LifecycleOwner接口,并且初始化了LifecycleRegistry
2.addObserver分析
上面了解了lifecycle的实例,那么我们就从LifecycleRegistry入手,首先看addObserver方法,我们只管传入的参数哪里去了,也就是说我们只需要看ObserverWithState做了什么事.
ObserverWithState会调用Lifecycling.lifecycleEventObserver方法,然后创建ReflectiveGenericLifecycleObserver对象,然后调用ClassesInfoCache.sInstance.getInfo,这个方法传入的是我们的MytViewModelLifecycle的对象,拿到他的class,然后通过反射拿到MytViewModelLifecycle方法和注解并且存入map.具体怎么反射这里就不细讲了! (在反射中一般都是通过map去存取提高性能)
3.观察者(MytViewModelLifecycle)是如何知道被观察者(Activity)的生命周期的
回到ComponentActivity中的onCreate方法,它会创建一个空白的ReportFragment,有了这个ReportFragment,当activity执行生命周期ReportFragment也会执行相应的生命周期. 我们以onStart为例,每个生命周期都会调用dispatch方法,最终都会调用**dispatch( Activity activity, Lifecycle.Event event)方法. 然后调用((LifecycleRegistry) lifecycle).handleLifecycleEvent(event)方法
在handleLifecycleEvent分别会调用getStateAfter和moveToState方法这两个方法,getStateAfter的目的就是通过生命周期得到一个状态.方便大家理解大家可以看白色背景的那张图.通过不同的事件拿到相应的状态
1.初始化状态->页面显示状态,这种情况属于activity的创建到显示 这属于前进状态
2.页面显示状态->销毁状态:这种情况下属于activity回到不可见了 这属于倒退状态
moveToState(next):这个方法的意思就是状态对齐.举个栗子吧:假如activity(被观察者)现在是onstart状态,这时候观察者MytViewModelLifecycle还是CREATE状态,这时候为了保证生命周期对齐,所以需要将next赋值给State,接着调用sync()进行同步
backwardPass方法 如果满足条件的主要调用downEvent 这个方法主要通过状态拿到事件,例如现在是STARTED对应上面的图拿到ON_STOP事件,然后又通过getStateAfter(ON_STOP)方法去拿到CREATED状态,
LifecycleEventObserver是一个接口 然后ReflectiveGenericLifecycleObserver实现了这个接口,所以最终调用了ReflectiveGenericLifecycleObserver的onStateChanged方法
invokeCallbacks方法里面通过反射拿到执行相应方法,这里就不多阐述了!
再回到sync()里面的forwardPass方法 如果满足条件的主要调用upEvent(observer.mState)拿到前进状态,例如现在是STARTED状态就可以到ON_RESUME事件通过ON_RESUME事件最终通过反射调用@OnLifecycleEvent(Lifecycle.Event.ON_RESUME)的方法
总结一下:
1.ComponentActivity里面实现了LifecycleOwner接口 ,并且初始化LifecycleRegistry了,LifecycleRegistry是实现了LifecycleOwner接口
2.在ComponentActivity里面创建了一个透明的ReportFragment来感应activity的生命周期,在Fragment的生命周期方法里面分别执行对应的dispatch方法
2.addObserver方法创建了ReflectiveGenericLifecycleObserver并且存储了观察者的class信息,
3.在dispatch传入相应的事件之后,然后通过getStateAfter拿到相应的状态
4.通过状态枚举比大小,如果是倒退流程就调用backwardPass方法,backwardPass方法会通过downEvent拿到状态拿到事件,然后又通过事件拿到状态
5.,如果是前进流程就调用forwardPass方法,forwardPass方法会通过upEvent拿到状态拿到事件
6.最后在ReflectiveGenericLifecycleObserver.onStateChanged里面执行mInfo.invokeCallbacks执行相应的方法
7.之所以要设计状态 是要留给其他框架用的
Android AAC第一篇 Lifecycle的源码解析
前言
AAC是Android Architecture Components的缩写，翻译过来就是Android架构组件的意思，是Google IO 2017大会期间发布的一组架构组件，它可以用来帮助开发搭建更加简单便捷的APP架构。AAC里面涉及到了LiveData，ViewModel，其中LiveData的工作需要依赖于Lifecycle，所以本篇文章将介绍Lifecycle的工作原理，并从源码的角度去解析它。在进行源码解读前我们需要先知道Lifecycle的使用方法，下面先看一个简单的simple。
这里我们新建Activity继承androidx里面的AppCompatActivity，它已经实现了LifecycleOwner接口，我们可以通过它的getLifecycle方法拿到这个lifecycle对象添加observer，如果是自己实现的Activity，那么可以在自定义的Activity中新建一个LifecycleRegistry并在响应的生命周期中调用它的handleLifecycleEvent方法监听生命周期的改变。
class LifecycleTestActivity : AppCompatActivity()
val TAG = javaClass.simpleName
override fun onCreate(savedInstanceState: Bundle?)
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_lifecycle_test)
lifecycle.addObserver(MyLifeCycleObserver())
MyLifeCycleObserver .java
class MyLifeCycleObserver : LifecycleObserver
val TAG = javaClass.simpleName
@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
fun onCreate()
Log.i(TAG, "onCreate-----");
@OnLifecycleEvent(Lifecycle.Event.ON_START)
fun onStart()
Log.i(TAG, "onStart-----");
@OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
fun onResume()
Log.i(TAG, "onResume-----");
@OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
fun onPause()
Log.i(TAG, "onPause-----");
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
fun onStop()
Log.i(TAG, "onStop-----");
@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
fun onDestroy()
Log.i(TAG, "onDestroy-----");
这样我们就可以监听到Activity的生命周期回调了。
源码解析
Lifecycle是androidx或者support包中新加入的功能特性，用来管理Activity的生命周期。本文以androidx包为例，进行源码解析。
在androidx包我们根据AppCompatActivity的继承关系可以发现它是ComponentActivity.java的子类，我们先看一下ComponentActivity.java的类结构
public class ComponentActivity extends Activity
implements LifecycleOwner, KeyEventDispatcher.Component
发现其实现了LifecycleOwner接口，我们看一下LifecycleOwner接口的定义
public interface LifecycleOwner
/**
* Returns the Lifecycle of the provider.
*
* @return The lifecycle of the provider.
*/
@NonNull
Lifecycle getLifecycle();
它定义了一个getLifecycle()方法，我们看看在ComponentActivity中这个接口方法的实现
@Override
public Lifecycle getLifecycle()
return mLifecycleRegistry;
发现这个方法返回的是一个Lifecycle对象，Lifecycle是一个抽象类，里面定义了三个抽象方法，和Event，State两个枚举类，我们看一下它的源码（限于篇幅，已裁剪掉了大段注释）
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
ON_CREATE,
ON_START,
ON_RESUME,
ON_PAUSE,
ON_STOP,
ON_DESTROY,
ON_ANY
/**
* Lifecycle states. You can consider the states as the nodes in a graph and
* @link Events as the edges between these nodes.
*/
@SuppressWarnings("WeakerAccess")
public enum State
DESTROYED,
INITIALIZED,
CREATED,
STARTED,
RESUMED;
public boolean isAtLeast(@NonNull State state)
return compareTo(state) >= 0;
在getLifecycle方法中，它返回的mLifecycleRegistry是一个LifecycleRegistry类的实例，我们看看它是怎么实现Lifecycle接口的，首先看看它的addObserver方法的源码
@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();
// mState / subling may have been changed recalculate
targetState = calculateTargetState(observer);
if (!isReentrance)
// we do sync only on the top level.
sync();
mAddingObserverCounter--;
在第二段代码中根据我们传入的observer创建了一个ObserverWithState类对象，我们看看ObserverWithState类对象
static class ObserverWithState
State mState;
GenericLifecycleObserver mLifecycleObserver;
ObserverWithState(LifecycleObserver observer, State initialState)
mLifecycleObserver = Lifecycling.getCallback(observer);
mState = initialState;
void dispatchEvent(LifecycleOwner owner, Event event)
State newState = getStateAfter(event);
mState = min(mState, newState);
mLifecycleObserver.onStateChanged(owner, event);
mState = newState;
注意看它的构造方法，它将我们传入的observer转化为了GenericLifecycleObserver类对象，而我们传入的对象仅是实现了一个空接口LifecycleObserver的实例，那么它是怎么转化的呢，我们看看Lifecycling.getCallback(observer);
@NonNull
static GenericLifecycleObserver getCallback(Object object)
// 如果是FullLifecycleObserver实例，那么创建一个FullLifecycleObserverAdapter对象
// FullLifecycleObserverAdapter实现了GenericLifecycleObserver接口
// ①.
if (object instanceof FullLifecycleObserver)
return new FullLifecycleObserverAdapter((FullLifecycleObserver) object);
// 如果是GenericLifecycleObserver对象，则不用转化了直接返回
// ②.
if (object instanceof GenericLifecycleObserver)
return (GenericLifecycleObserver) object;
final Class<?> klass = object.getClass();
// 获取需要转化是通过反射还是生成类型
// ③.
int type = getObserverConstructorType(klass);
if (type == GENERATED_CALLBACK)
// 生成类型
List<Constructor<? extends GeneratedAdapter>> constructors =
sClassToAdapters.get(klass);
if (constructors.size() == 1)
GeneratedAdapter generatedAdapter = createGeneratedAdapter(
constructors.get(0), object);
// ④.
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);
// ④.
return new CompositeGeneratedAdaptersObserver(adapters);
// ④.
return new ReflectiveGenericLifecycleObserver(object);
这个方法比较复杂，我们首先看下1处的FullLifecycleObserver接口
interface FullLifecycleObserver extends LifecycleObserver
void onCreate(LifecycleOwner owner);
void onStart(LifecycleOwner owner);
void onResume(LifecycleOwner owner);
void onPause(LifecycleOwner owner);
void onStop(LifecycleOwner owner);
void onDestroy(LifecycleOwner owner);
发现它定义了一组和Activity生命周期相对应的方法，我们在看看FullLifecycleObserverAdapter
class FullLifecycleObserverAdapter implements GenericLifecycleObserver
private final FullLifecycleObserver mObserver;
FullLifecycleObserverAdapter(FullLifecycleObserver observer)
mObserver = observer;
@Override
public void onStateChanged(LifecycleOwner source, Lifecycle.Event event)
switch (event)
case ON_CREATE:
mObserver.onCreate(source);
break;
case ON_START:
mObserver.onStart(source);
break;
case ON_RESUME:
mObserver.onResume(source);
break;
case ON_PAUSE:
mObserver.onPause(source);
break;
case ON_STOP:
mObserver.onStop(source);
break;
case ON_DESTROY:
mObserver.onDestroy(source);
break;
case ON_ANY:
throw new IllegalArgumentException("ON_ANY must not been send by anybody");
可以发现它应用了适配器模式，实现了GenericLifecycleObserver接口，在接口方法onStateChanged实现中回调了相应的方法，将。这FullLifecycleObserver接口适配成了GenericLifecycleObserver。这里我们先记住GenericLifecycleObserver接口，它比较重要，后面我们会知道GenericLifecycleObserver接口的onStateChanged触发点。通过对FullLifecycleObserver和FullLifecycleObserverAdapter分析我们得出，如果我们添加的observer是FullLifecycleObserver的实例，那么它最终也会转换为GenericLifecycleObserver，可惜FullLifecycleObserver的访问权限是默认的不是public的。
我们再看上面的②处，如果我们传入的observer是GenericLifecycleObserver实例，那么它直接返回。再看上面的③处的getObserverConstructorType方法
private static int getObserverConstructorType(Class<?> klass)
if (sCallbackCache.containsKey(klass))
return sCallbackCache.get(klass);
int type = resolveObserverCallbackType(klass);
sCallbackCache.put(klass, type);
return type;
它做了缓存，然后调用了resolveObserverCallbackType方法
private static int resolveObserverCallbackType(Class<?> klass)
// anonymous class bug:35073837
// 判断是不是匿名内部类，为null代表是匿名内部类
if (klass.getCanonicalName() == null)
return REFLECTIVE_CALLBACK;
// 反射获取构造器，内部根据传入的class和约定的_LifecycleAdapter命名后缀反射加载相应注解生成器生成的构造器
Constructor<? extends GeneratedAdapter> constructor = generatedConstructor(klass);
if (constructor != null)
sClassToAdapters.put(klass, Collections
.<Constructor<? extends GeneratedAdapter>>singletonList(constructor));
// 有相应的构造器，返回生成类型
return GENERATED_CALLBACK;
// 反射获取observer类的方法，判断它是否包含OnLifecycleEvent.class注解，如果包含，则返回反射类型
boolean hasLifecycleMethods = ClassesInfoCache.sInstance.hasLifecycleMethods(klass);
if (hasLifecycleMethods)
return REFLECTIVE_CALLBACK;
Class<?> superclass = klass.getSuperclass();
List<Constructor<? extends GeneratedAdapter>> adapterConstructors = null;
// 判断observer的superclass是否是LifecycleObserver的子类
if (isLifecycleParent(superclass))
// 判断父类型是否符合反射类型
if (getObserverConstructorType(superclass) == REFLECTIVE_CALLBACK)
return REFLECTIVE_CALLBACK;
adapterConstructors = new ArrayList<>(sClassToAdapters.get(superclass));
// 判断observer实现的接口是否符合反射类型
for (Class<?> intrface : klass.getInterfaces())
if (!isLifecycleParent(intrface))
continue;
if (getObserverConstructorType(intrface) == REFLECTIVE_CALLBACK)
return REFLECTIVE_CALLBACK;
// 生成类的构造器
if (adapterConstructors == null)
adapterConstructors = new ArrayList<>();
adapterConstructors.addAll(sClassToAdapters.get(intrface));
// 判断是否反射解析到生成类的构造器
if (adapterConstructors != null)
sClassToAdapters.put(klass, adapterConstructors);
return GENERATED_CALLBACK;
return REFLECTIVE_CALLBACK;
通过上面的注释我们发现getObserverConstructorType方法是生成observer转化类是通过反射还是注解生成的类。回到调用getObserverConstructorType的getCallback方法
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);
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);
通过getObserverConstructorType方法得到通过反射还是生成得到代理的observer的类，如果是生成类型则会更加构造器的数量生成SingleGeneratedAdapterObserver或是CompositeGeneratedAdaptersObserver，如果是反射方式则会生成ReflectiveGenericLifecycleObserver，我们分别看下这三个类的源码
SingleGeneratedAdapterObserver.java
public class SingleGeneratedAdapterObserver implements GenericLifecycleObserver
private final GeneratedAdapter mGeneratedAdapter;
SingleGeneratedAdapterObserver(GeneratedAdapter generatedAdapter)
mGeneratedAdapter = generatedAdapter;
@Override
public void onStateChanged(LifecycleOwner source, Lifecycle.Event event)
mGeneratedAdapter.callMethods(source, event, false, null);
mGeneratedAdapter.callMethods(source, event, true, null);
CompositeGeneratedAdaptersObserver.java
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
public class CompositeGeneratedAdaptersObserver implements GenericLifecycleObserver
private final GeneratedAdapter[] mGeneratedAdapters;
CompositeGeneratedAdaptersObserver(GeneratedAdapter[] generatedAdapters)
mGeneratedAdapters = generatedAdapters;
@Override
public void onStateChanged(LifecycleOwner source, Lifecycle.Event event)
MethodCallsLogger logger = new MethodCallsLogger();
for (GeneratedAdapter mGenerated: mGeneratedAdapters)
mGenerated.callMethods(source, event, false, logger);
for (GeneratedAdapter mGenerated: mGeneratedAdapters)
mGenerated.callMethods(source, event, true, logger);
ReflectiveGenericLifecycleObserver .java
class ReflectiveGenericLifecycleObserver implements GenericLifecycleObserver
private final Object mWrapped;
private final CallbackInfo mInfo;
ReflectiveGenericLifecycleObserver(Object wrapped)
mWrapped = wrapped;
mInfo = ClassesInfoCache.sInstance.getInfo(mWrapped.getClass());
@Override
public void onStateChanged(LifecycleOwner source, Event event)
mInfo.以上是关于Android Lifecycle源码解析的主要内容，如果未能解决你的问题，请参考以下文章