Android系统启动流程(四)Launcher启动过程与系统启动流程

Android系统启动流程（四）Launcher 启动过程与系统启动流程前言此前的文章我们学习了init进程、Zygote进程和SyetemServer进程的启动过程，这一篇文章我们就来学习Android系统启动流程的最后一步：Launcher的启动流程，并结合本系列的前三篇文章的内容来讲解Android系统启动流程。

建议读这篇文章前要通读本系列的前三篇文章，否则你可能不会理解我在讲什么。

uncher概述Android系统启动的最后一步是启动一个Home应用程序，这个应用程序用来显示系统中已经安装的应用程序，这个Home应用程序就叫做Launcher。

应用程序Launcher在启动过程中会请求PackageManagerService返回系统中已经安装的应用程序的信息，并将这些信息封装成一个快捷图标列表显示在系统屏幕上，这样用户可以通过点击这些快捷图标来启动相应的应用程序。

uncher启动流程SyetemServer进程在启动的过程中会启动PackageManagerService，PackageManagerService 启动后会将系统中的应用程序安装完成。

在此前已经启动的ActivityManagerService会将Launcher启动起来。

启动Launcher的入口为ActivityManagerService的systemReady函数，如下所示。

frameworks/base/services/Java/com/android/server/SystemServer.javaprivate void startOtherServices() {...mActivityManagerService.systemReady(new Runnable() {@Overridepublic void run() {Slog.i(TAG, "Making services ready");mSystemServiceManager.startBootPhase(SystemService.PHASE_ACTIVITY_MANAGER_READY);...}...}在startOtherServices函数中，会调用ActivityManagerService的systemReady函数：frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.javapublic void systemReady(final Runnable goingCallback) {...synchronized (this) {...mStackSupervisor.resumeFocusedStackTopActivityLocked();mUserController.sendUserSwitchBroadcastsLocked(-1, currentUserId);}}systemReady函数中调用了ActivityStackSupervisor的resumeFocusedStackTopActivityLocked 函数：frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.javaboolean resumeFocusedStackTopActivityLocked(ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) { if (targetStack != null && isFocusedStack(targetStack)) {return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);//1 }final ActivityRecord r = mFocusedStack.topRunningActivityLocked();if (r == null || r.state != RESUMED) {mFocusedStack.resumeTopActivityUncheckedLocked(null, null);}return false;}在注释1处会调用ActivityStack的resumeTopActivityUncheckedLocked函数，ActivityStack 对象是用来描述Activity堆栈的，resumeTopActivityUncheckedLocked函数如下所示。

frameworks/base/services/core/java/com/android/server/am/ActivityStack.javaboolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) { if (mStackSupervisor.inResumeTopActivity) {// Don't even start recursing.return false;}boolean result = false;try {// Protect against recursion.mStackSupervisor.inResumeTopActivity = true;if (mService.mLockScreenShown == ActivityManagerService.LOCK_SCREEN_LEA VING) {mService.mLockScreenShown = ActivityManagerService.LOCK_SCREEN_HIDDEN;mService.updateSleepIfNeededLocked();}result = resumeTopActivityInnerLocked(prev, options);//1} finally {mStackSupervisor.inResumeTopActivity = false;}return result;}注释1调用了resumeTopActivityInnerLocked函数：private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) { ...return isOnHomeDisplay() &&mStackSupervisor.resumeHomeStackTask(returnTaskType, prev, "prevFinished");...}resumeTopActivityInnerLocked函数的代码很长，我们截取我们要分析的关键的一句：调用ActivityStackSupervisor的resumeHomeStackTask函数，代码如下所示。

frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.javaboolean resumeHomeStackTask(int homeStackTaskType, ActivityRecord prev, String reason) { ...if (r != null && !r.finishing) {mService.setFocusedActivityLocked(r, myReason);return resumeFocusedStackTopActivityLocked(mHomeStack, prev, null);}return mService.startHomeActivityLocked(mCurrentUser, myReason);//1}在注释1处调用了ActivityManagerService的startHomeActivityLocked函数，如下所示。

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.javaboolean startHomeActivityLocked(int userId, String reason) {if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL&& mTopAction == null) {//1return false;}Intent intent = getHomeIntent();//2ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);if (aInfo != null) {intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, ));aInfo = new ActivityInfo(aInfo);aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);ProcessRecord app = getProcessRecordLocked(aInfo.processName,aInfo.applicationInfo.uid, true);if (app == null || app.instrumentationClass == null) {//3intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);mActivityStarter.startHomeActivityLocked(intent, aInfo, reason);//4}} else {Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());}return true;}注释1处的mFactoryTest代表系统的运行模式，系统的运行模式分为三种，分别是非工厂模式、低级工厂模式和高级工厂模式，mTopAction则用来描述第一个被启动Activity组件的Action，它的值为Intent.ACTION_MAIN。