AMS之Activity生命周期原理

一：开始请求执行启动Activity

MyActivity.startActivity() 
Activity.startActivity() 
Activity.startActivityForResult 
Instrumentation.execStartActivty 
ActivityManagerNative.getDefault().startActivityAsUser()

二：ActivityManagerService接收启动Activity的请求

ActivityManagerService.startActivity() 
ActivityManagerService.startActivityAsUser() 
ActivityStackSupervisor.startActivityMayWait() 
ActivityStackSupervisor.startActivityLocked() 
ActivityStackSupervisor.startActivityUncheckedLocked() 
ActivityStackSupervisor.startActivityLocked() 
ActivityStackSupervisor.resumeTopActivitiesLocked() 
ActivityStackSupervisor.resumeTopActivityInnerLocked()

三：执行栈顶Activity的onPause方法

ActivityStack.startPausingLocked() 
IApplicationThread.schudulePauseActivity() 
ActivityThread.sendMessage() 
ActivityThread.H.sendMessage(); 
ActivityThread.H.handleMessage() 
ActivityThread.handlePauseActivity() 
ActivityThread.performPauseActivity() 
Activity.performPause() 
Activity.onPause() 
ActivityManagerNative.getDefault().activityPaused(token) 
ActivityManagerService.activityPaused() 
ActivityStack.activityPausedLocked() 
ActivityStack.completePauseLocked() 
ActivityStack.resumeTopActivitiesLocked() 
ActivityStack.resumeTopActivityLocked() 
ActivityStack.resumeTopActivityInnerLocked() 
ActivityStack.startSpecificActivityLocked

四：启动Activity所属的应用进程

ActivityManagerService.startProcessLocked() 
Process.start() 
ActivityThread.main() 
ActivityThread.attach() 
ActivityManagerNative.getDefault().attachApplication() 
ActivityManagerService.attachApplication()

五：执行启动Acitivity

ActivityStackSupervisor.attachApplicationLocked() 
ActivityStackSupervisor.realStartActivityLocked() 
IApplicationThread.scheduleLauncherActivity() 
ActivityThread.sendMessage() 
ActivityThread.H.sendMessage() 
ActivityThread.H.handleMessage() 
ActivityThread.handleLauncherActivity() 
ActivityThread.performLauncherActivity() 
Instrumentation.callActivityOnCreate() 
Activity.onCreate() 
ActivityThread.handleResumeActivity() 
ActivityThread.performResumeActivity() 
Activity.performResume() 
Instrumentation.callActivityOnResume() 
Activity.onResume() 
ActivityManagerNative.getDefault().activityResumed(token)

六：栈顶Activity执行onStop方法

Looper.myQueue().addIdleHandler(new Idler()) 
Idler.queueIdle() 
ActivityManagerNative.getDefault().activityIdle() 
ActivityManagerService.activityIdle() 
ActivityStackSupervisor.activityIdleInternalLocked() 
ActivityStack.stopActivityLocked() 
IApplicationThread.scheduleStopActivity() 
ActivityThread.scheduleStopActivity() 
ActivityThread.sendMessage() 
ActivityThread.H.sendMessage() 
ActivityThread.H.handleMessage() 
ActivityThread.handleStopActivity() 
ActivityThread.performStopActivityInner() 
ActivityThread.callCallActivityOnSaveInstanceState() 
Instrumentation.callActivityOnSaveInstanceState() 
Activity.performSaveInstanceState() 
Activity.onSaveInstanceState() 
Activity.performStop() 
Instrumentation.callActivityOnStop() 
Activity.onStop()

总结：

1、Activity的启动流程一般是通过调用startActivity或者是startActivityForResult来开始的

2、startActivity内部也是通过调用startActivityForResult来启动Activity，只不过传递的requestCode小于0

3、Activity的启动流程涉及到多个进程之间的通讯这里主要是ActivityThread与ActivityManagerService之间的通讯

4、ActivityThread向ActivityManagerService传递进程间消息通过ActivityManagerNative，ActivityManagerService向ActivityThread进程间传递消息通过IApplicationThread。

5、ActivityManagerService接收到应用进程创建Activity的请求之后会执行初始化操作，解析启动模式，保存请求信息等一系列操作。

6、ActivityManagerService保存完请求信息之后会将当前系统栈顶的Activity执行onPause操作，并且IApplication进程间通讯告诉应用程序继承执行当前栈顶的Activity的onPause方法；

7、ActivityThread接收到SystemServer的消息之后会统一交个自身定义的Handler对象处理分发；

8、ActivityThread执行完栈顶的Activity的onPause方法之后会通过ActivityManagerNative执行进程间通讯告诉ActivityManagerService，栈顶Actiity已经执行完成onPause方法，继续执行后续操作；

9、ActivityManagerService会继续执行启动Activity的逻辑，这时候会判断需要启动的Activity所属的应用进程是否已经启动，若没有启动则首先会启动这个Activity的应用程序进程；

10、ActivityManagerService会通过socket与Zygote继承通讯，并告知Zygote进程fork出一个新的应用程序进程，然后执行ActivityThread的mani方法；

11、在ActivityThead.main方法中执行初始化操作，初始化主线程异步消息，然后通知ActivityManagerService执行进程初始化操作；

12、ActivityManagerService会在执行初始化操作的同时检测当前进程是否有需要创建的Activity对象，若有的话，则执行创建操作；

13、ActivityManagerService将执行创建Activity的通知告知ActivityThread，然后通过反射机制创建出Activity对象，并执行Activity的onCreate方法，onStart方法，onResume方法；

14、ActivityThread执行完成onResume方法之后告知ActivityManagerService onResume执行完成，开始执行栈顶Activity的onStop方法；

15、ActivityManagerService开始执行栈顶的onStop方法并告知ActivityThread；

16、ActivityThread执行真正的onStop方法；