Android 8.0系统启动流程

本系列主要介绍Android8.0系统启动过程中涉及到的init、Zygote、SystemServer和Launcher。
在之前的三篇文章中，讲解了如下的过程：

初始化化：电源上电，加载BootLoader程序；启动init.cpp，解析init.rc配置文件；
启动Zygote进程：启动虚拟机和注册JNI方法；注册Socket服务端，预加载资源；执行runSelectLoop(）方法等待其他进程的注册；
启动SystemServer进程：通过Zygote启动，创建Binder线程池、执行main方法；开启三个系统服务（引导、核心和其他）。

在完成以上三个过程后，我们的系统就开始加载Launcher应用，查看源码可以发现Launcher是作为一个APP应用执行的，其一般位于系统的packages/apps目录下，可以通过该应用启动系统中其他应用程序，提供快捷访问图标。

一、Launcher的启动

1.1启动准备

在SystemServer启动时，会先启动引导服务，其中包括PMS（PackageManagerService）和AMS(ActivityManagerService)，其中PMS主要作用是系统中的APK的解析和安装；AMS主要用于四大组件的启动和管理，因此LauncherActivity通过AMS启动。
完成引导服务的启动后，开启启动其他服务。启动Launcher的入口为AMS的systemReady方法，

frameworks\base\services\java\com\android\server\SystemServer.javaprivate void startOtherServices() {...//在此之前会做大量的准备工作，包括AMS、PMS 和NetworkScoreService等各种服务，完成以上操作后，表示activity manager可以运行mActivityManagerService.systemReady(() -> {Slog.i(TAG, "Making services ready");traceBeginAndSlog("StartActivityManagerReadyPhase");mSystemServiceManager.startBootPhase(SystemService.PHASE_ACTIVITY_MANAGER_READY);...}......
}

frameworks\base\services\core\java\com\android\server\am\ActivityManagerService.javapublic void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {traceLog.traceBegin("PhaseActivityManagerReady");synchronized(this) {
...mStackSupervisor.resumeFocusedStackTopActivityLocked();mUserController.sendUserSwitchBroadcastsLocked(-1, currentUserId);
...}
}

1.2找到Launcher 的Activity

AMS通过调用ActivityStack实现对堆栈中Activity对象的管理，我们的最终目的是查找到Launcher应用所在的Activity是如何被调用起来的？
其流程如下：
ActivityStackSuperior#resumeFocusedStackTopActivityLocked() ->ActivityStack#resumeTopActivityUncheckedLocked()->resumeTopActivityInnerLocked()
在resumeTopActivityInnerLocked中，通过调用startHomeActivityLocked方法，开启启动Launcher的Activty。

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);}...return false;

frameworks\base\services\core\java\com\android\server\am\ActivityStack.java
boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
if (mStackSupervisor.inResumeTopActivity) {return false;}boolean result = false;try {mStackSupervisor.inResumeTopActivity = true;result = resumeTopActivityInnerLocked(prev, options);} finally {mStackSupervisor.inResumeTopActivity = false;}final ActivityRecord next = topRunningActivityLocked(true /* focusableOnly */);if (next == null || !next.canTurnScreenOn()) {checkReadyForSleep();}return result;
}

frameworks\base\services\core\java\com\android\server\am\ActivityStackSupervisor.javaprivate boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {...
return isOnHomeDisplay() &&mStackSupervisor.resumeHomeStackTask(prev, reason);...if (r != null && !r.finishing) {moveFocusableActivityStackToFrontLocked(r, myReason);return resumeFocusedStackTopActivityLocked(mHomeStack, prev, null);}return mService.startHomeActivityLocked(mCurrentUser, myReason);
...
}

1.3 启动Launcher

frameworks\base\services\core\java\com\android\server\am\ActivityManagerService.javaboolean startHomeActivityLocked(int userId, String reason) {//1 判断工厂模式和topAction
if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL&& mTopAction == null) {return false;}//2 创建启动Launcher的IntentIntent intent = getHomeIntent();ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);if (aInfo != null) {intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));aInfo = new ActivityInfo(aInfo);aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);ProcessRecord app = getProcessRecordLocked(aInfo.processName,aInfo.applicationInfo.uid, true);if (app == null || app.instr == null) {intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);final int resolvedUserId = UserHandle.getUserId(aInfo.applicationInfo.uid); final String myReason = reason + ":" + userId + ":" + resolvedUserId;//3 启动LauncdrmActivityStarter.startHomeActivityLocked(intent, aInfo, myReason);}} else {Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());}return true;
}

在注释1处是对运行模式和Action的判断，其中运行模式包括：非工厂模式、低级工厂模式和高级工厂模式。而Action的是是指启动该Intent的Action，默认是Intent.ACTION_MAIN，表示是该应用的第一个启动的Activity，一般在创建应用时，AndroidMainfest.xm中都会包含唯一个该标签的Action。
而对于桌面应用，会增加Intent.HOME的标签，如果我们想自定义桌面应用，可在该应用的AndroidMainfest中的启动Activity的Action添加android.Intent.action.HOME，如下所示：

 <application...<activity android:name=".MainActivity"><intent-filter><action android:name="android.intent.action.HOME"/><action android:name="android.intent.action.MAIN"/><category android:name="android.intent.category.LAUNCHER"/></intent-filter></activity></application>

启动Launer是在ActivityStarter的startHomeActivityLocked方法中完成，通过ActivityStackSupervisor将该Intent移动至HomeStack(用于存储Launcher的变量)的顶部，最终调用startActivityLocked方法启动该Intnet，实现对Launcer的启动。

 void startHomeActivityLocked(Intent intent, ActivityInfo aInfo, String reason) {mSupervisor.moveHomeStackTaskToTop(reason);...}

二、Launcher桌面图标显示

完成Launcer的启动后，作为一个独立的APP，Launcher开始执行应用的加载和桌面图标的显示。

2.1 加载APP

packages\apps\Launcher3\src\com\android\launcher3\Launcher.java
protected void onCreate(Bundle savedInstanceState) {
...
//加载桌面颜色信息和监听主题变化WallpaperColorInfo wallpaperColorInfo = WallpaperColorInfo.getInstance(this);wallpaperColorInfo.setOnThemeChangeListener(this);
...
//加载桌面应用信息LauncherAppState app = LauncherAppState.getInstance(this);...mModel = app.setLauncher(this);...//加载和设置桌面viewmLauncherView = LayoutInflater.from(this).inflate(R.layout.launcher, null);setupViews();...if (!mModel.startLoader(currentScreen)) {mDragLayer.setAlpha(0);} else {mWorkspace.setCurrentPage(currentScreen);setWorkspaceLoading(true);}
}

//设置launcher的监听，初始化model
packages\apps\Launcher3\src\com\android\launcher3\LauncherAppStateLauncherModel setLauncher(Launcher launcher) {getLocalProvider(mContext).setLauncherProviderChangeListener(launcher);mModel.initialize(launcher); //传入Launcher对象return mModel;}

在设置监听时，传入的Callbacks 对象时Launcher，是为了在APP加载完成时，方便通过接口回调的形式返回值Launcher，
下面开始加载App。

packages\apps\Launcher3\src\com\android\launcher3\LauncherModelpublic void initialize(Callbacks callbacks) {synchronized (mLock) {Preconditions.assertUIThread();mCallbacks = new WeakReference<>(callbacks);}}//Callbacks 接口包含的内容如下，主要用到bindAllApplications
public interface Callbacks extends LauncherAppWidgetHost.ProviderChangedListener {...public void bindAllApplications(ArrayList<AppInfo> apps);public void bindAppsAddedOrUpdated(ArrayList<AppInfo> apps);public void bindAppsAdded(ArrayList<Long> newScreens,ArrayList<ItemInfo> addNotAnimated,ArrayList<ItemInfo> addAnimated);public void bindPromiseAppProgressUpdated(PromiseAppInfo app);public void bindShortcutsChanged(ArrayList<ShortcutInfo> updated, UserHandle user);public void bindWidgetsRestored(ArrayList<LauncherAppWidgetInfo> widgets);public void bindRestoreItemsChange(HashSet<ItemInfo> updates);public void bindWorkspaceComponentsRemoved(ItemInfoMatcher matcher);public void bindAppInfosRemoved(ArrayList<AppInfo> appInfos);public void bindAllWidgets(MultiHashMap<PackageItemInfo, WidgetItem> widgets);...}

加载的Task分析如下

...
packages\apps\Launcher3\src\com\android\launcher3\LauncherModel
//开始加载
public boolean startLoader(int synchronousBindPage) {...synchronized (mLock) {//清除之前的回调缓存if (mCallbacks != null && mCallbacks.get() != null) {final Callbacks oldCallbacks = mCallbacks.get();// Clear any pending bind-runnables from the synchronized load process.mUiExecutor.execute(new Runnable() {public void run() {oldCallbacks.clearPendingBinds();}});// If there is already one running, tell it to stop.stopLoader();LoaderResults loaderResults = new LoaderResults(mApp, sBgDataModel,mBgAllAppsList, synchronousBindPage, mCallbacks);//包含Callbacks对象if (mModelLoaded && !mIsLoaderTaskRunning) {    //已经加载完成且没有正在加载//加载完成后，开始将结果回调至LauncherloaderResults.bindWorkspace();loaderResults.bindAllApps(); //加载的回调loaderResults.bindDeepShortcuts();loaderResults.bindWidgets();return true;} else {//开始不断的加载 工作区间、所有的APP、快捷图标和抽屉控件startLoaderForResults(loaderResults);}}}return false;}packages\apps\Launcher3\src\com\android\launcher3\LauncherModel
public void startLoaderForResults(LoaderResults results) {synchronized (mLock) {//停止加载stopLoader();//创建新的加载taskmLoaderTask = new LoaderTask(mApp, mBgAllAppsList, sBgDataModel, results);//在WorkerThread中执行该taskrunOnWorkerThread(mLoaderTask);}}//加载中涉及的线程初始化packages\apps\Launcher3\src\com\android\launcher3\LauncherModel
@Thunk static final HandlerThread sWorkerThread = new HandlerThread("launcher-loader");static {sWorkerThread.start();}
@Thunk static final Handler sWorker = new Handler(sWorkerThread.getLooper());

2.2 加载回调处理

通过LauncherModel的加载线程，获取到了系统中所有的apps的信息，同时通过其Callbacks的接口，很方便的将结果传递出去，

packages\apps\Launcher3\src\com\android\launcher3\Launcher.java
public void bindAllApplications(final ArrayList<AppInfo> apps) {Runnable r = new RunnableWithId(RUNNABLE_ID_BIND_APPS) {public void run() {bindAllApplications(apps);}};...//加载完成后AllAppsContainerView数据更新mAppsView.setApps(apps);}if (mLauncherCallbacks != null) {mLauncherCallbacks.bindAllApplications(apps);}}

数据回调值Launcher的bindAllApplications，开始对AllAppsContainerView界面进行数据设置，其设置的控制控件为AlphabeticalAppsList，通过调用AlphabeticalAppsList实现对数据的设置处理，其实现流程和Recycleview的设置比较类似。

packages\apps\Launcher3\src\com\android\launcher3\allapps\AllAppsContainerView.javapublic void setApps(List<AppInfo> apps) {mApps.setApps(apps);}//数据传递控制控件中
packages\apps\Launcher3\src\com\android\launcher3\allapps\AlphabeticalAppsList.java
public void setApps(List<AppInfo> apps) {mComponentToAppMap.clear();addOrUpdateApps(apps);}packages\apps\Launcher3\src\com\android\launcher3\allapps\AllAppsContainerView.java@Overrideprotected void onFinishInflate() {
...mAppsRecyclerView = findViewById(R.id.apps_list_view); //可以看到桌面应用部分的界面为RecyclerViewmAppsRecyclerView.setApps(mApps);mAppsRecyclerView.setLayoutManager(mLayoutManager);mAppsRecyclerView.setAdapter(mAdapter);mAppsRecyclerView.setHasFixedSize(true);
...}

AllAppsContainerView会在XML布局文件加载完成后，调用onFinishInflate方法，使加载的数据最终显示在桌面上。形成我们看到的桌面图标。

2.3 点击桌面图标的跳转至应用

在AllAppsContainerView设置adapter后，由于RecyclerView不包含setOnItemClickListener方法，因此一般是在Adapter中自定义实现，可通过回调的形式将点击事件传递出去，Launcher的执行流程如下：

//packages\apps\Launcher3\src\com\android\launcher3\allapps\AllAppsContainerView.javapublic AllAppsContainerView(Context context, AttributeSet attrs, int defStyleAttr) {...//创建新的AdaptermAdapter = new AllAppsGridAdapter(mLauncher, mApps, mLauncher, this);mSpringAnimationHandler = mAdapter.getSpringAnimationHandler();mApps.setAdapter(mAdapter);...}

设置点击的监听回调

//packages\apps\Launcher3\src\com\android\launcher3\allapps\AllAppsGridAdapter.javapublic AllAppsGridAdapter(Launcher launcher, AlphabeticalAppsList apps, View.OnClickListenericonClickListener, View.OnLongClickListener iconLongClickListener) {...mIconClickListener = iconClickListener;...}

点击事件的处理

packages\apps\Launcher3\src\com\android\launcher3\Launcher.javapublic void onClick(View v) {
...Object tag = v.getTag();if (tag instanceof ShortcutInfo) {onClickAppShortcut(v);} else if (tag instanceof FolderInfo) {if (v instanceof FolderIcon) {onClickFolderIcon(v);}} else if ((v instanceof PageIndicator) ||(v == mAllAppsButton && mAllAppsButton != null)) {onClickAllAppsButton(v);} else if (tag instanceof AppInfo) {startAppShortcutOrInfoActivity(v);} else if (tag instanceof LauncherAppWidgetInfo) {if (v instanceof PendingAppWidgetHostView) {onClickPendingWidget((PendingAppWidgetHostView) v);}}
}//点击桌面应用的快捷图标的处理
protected void onClickAppShortcut(final View v) {
...startAppShortcutOrInfoActivity(v);
...
}private void startAppShortcutOrInfoActivity(View v) {ItemInfo item = (ItemInfo) v.getTag();Intent intent;if (item instanceof PromiseAppInfo) {PromiseAppInfo promiseAppInfo = (PromiseAppInfo) item;intent = promiseAppInfo.getMarketIntent();} else {intent = item.getIntent();}...//跳转至相应的应用boolean success = startActivitySafely(v, intent, item);
...}

至此Launcher的启动过程便分析完，总结如下：

启动：SystemServer启动PMS和AMS，通过AMS的systemReady开始加载；
查找：查找流程如下ActivityStackSuperior#resumeFocusedStackTopActivityLocked() ->ActivityStack#resumeTopActivityUncheckedLocked()->resumeTopActivityInnerLocked()；
显示：在resumeTopActivityInnerLocked中通过调用startHomeActivityLocked方法，启动Launcher的Activty，通过LauncherModel的加载线程处理，获取到所有的Apps信息，借助Callbacks的接口回调的形式将数据返回值Launcher，然后将数据赋值给AllAppsContainerView，使Apps的桌面图标显示至桌面中。
跳转：通过设置点击事件的回调处理，点击桌面图标后，通过startActivitySafely跳转至应用的Main界面。