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；