Android应用程序框架之Home程序（Launcher）

上一篇博客我们讲了PackageManagerService的启动过程以及对于应用程序的注册过程，当系统启动完成后，系统需要开启第一个应用程序，这就是Home程序，也就是我们熟知的桌面程序。本篇博客主要介绍Home的启动过程。 通过上一篇博客介绍，我们知道系统在启动的时候会启动SystemServer,并且在SystemServer中会启动一系列的Service，包括PackageManagerService,ActivityManagerService等等，而ActivityManagerService在启动后就会负责Home的启动。所以一开始先来看看ActivityManagerService的启动。

1.ActivityManagerService

通过前一篇博客的介绍，我们知道SystemServer在启动后会开启一个线程ServerThread来启动各种系统级Service，其中就包括ActivityManagerService,ServerThread的run函数可以参看上一篇博客。接下来看看ActivityManagerService启动后都干些什么。

1 ActivityManagerService.main

public final class ActivityManagerService extends ActivityManagerNative implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback { ...... public static final Context main(int factoryTest) { AThread thr = new AThread(); thr.start(); synchronized (thr) { while (thr.mService == null) { try { thr.wait(); } catch (InterruptedException e) { } } } ActivityManagerService m = thr.mService; mSelf = m; ActivityThread at = ActivityThread.systemMain(); mSystemThread = at; Context context = at.getSystemContext(); m.mContext = context; m.mFactoryTest = factoryTest; m.mMainStack = new ActivityStack(m, context, true); m.mBatteryStatsService.publish(context); m.mUsageStatsService.publish(context); synchronized (thr) { thr.mReady = true; thr.notifyAll(); } m.startRunning(null, null, null, null); return context; } ...... }

这个函数首先通过AThread线程对象来内部创建了一个ActivityManagerService实例，然后将这个实例保存其成员变量mService中，接着又把这个ActivityManagerService实例保存在ActivityManagerService类的静态成员变量mSelf中，最后初始化其它成员变量，就结束了。

2.ActivityManagerService.setProcessSystem

public final class ActivityManagerService extends ActivityManagerNative implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback { ...... public static void setSystemProcess() { try { ActivityManagerService m = mSelf; ServiceManager.addService("activity", m); ServiceManager.addService("meminfo", new MemBinder(m)); if (MONITOR_CPU_USAGE) { ServiceManager.addService("cpuinfo", new CpuBinder(m)); } ServiceManager.addService("permission", new PermissionController(m)); ApplicationInfo info = mSelf.mContext.getPackageManager().getApplicationInfo( "android", STOCK_PM_FLAGS); mSystemThread.installSystemApplicationInfo(info); synchronized (mSelf) { ProcessRecord app = mSelf.newProcessRecordLocked( mSystemThread.getApplicationThread(), info, info.processName); app.persistent = true; app.pid = MY_PID; app.maxAdj = SYSTEM_ADJ; mSelf.mProcessNames.put(app.processName, app.info.uid, app); synchronized (mSelf.mPidsSelfLocked) { mSelf.mPidsSelfLocked.put(app.pid, app); } mSelf.updateLruProcessLocked(app, true, true); } } catch (PackageManager.NameNotFoundException e) { throw new RuntimeException( "Unable to find android system package", e); } } ...... }

这个函数主要做了两件事，第一是将ActivityManagerService实例添加到ServiceManager中，这样其他组件就可以通过getSystemService接口来获取到ActivityManagerSerivce了。 第二件事就是通过调用mSystemThread.installSystemApplicationInfo函数来把应用程序框架层下面的android包加载进来。

3.ActivityManagerService.systemReady

接下来ActivityManagerService会调用systemReadey接口。

public final class ActivityManagerService extends ActivityManagerNative implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback { ...... public void systemReady(final Runnable goingCallback) { ...... synchronized (this) { ...... mMainStack.resumeTopActivityLocked(null); } } ...... }

这里就是通过mMainStack.resumeTopActivityLocked函数来启动Home应用程序的了，这里的mMainStack是一个ActivityStack类型的实例变量。

2.Home应用程序启动

1.mMainStack.resumeTopActivityLocked

接着上面的指令流继续往下看，前文已经讲到了，mMainStack是一个ActivityStack，即一个activity的栈，每个应用程序都会有一个或多个ActivityStack用来维护activity。而resumeTopActivityLocked就是把栈顶的activity恢复到前台。

public class ActivityStack { ...... final boolean resumeTopActivityLocked(ActivityRecord prev) { // Find the first activity that is not finishing. ActivityRecord next = topRunningActivityLocked(null); ...... if (next == null) { // There are no more activities! Let's just start up the // Launcher... if (mMainStack) { return mService.startHomeActivityLocked(); } } ...... } ...... }

由于当前Home应用程序并没有启动，所以next为null，进而会调用mService.startHomeActivityLocked来启动Home程序。

2.mService.startHomeActivityLocked

public final class ActivityManagerService extends ActivityManagerNative implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback { ...... boolean startHomeActivityLocked() { ...... Intent intent = new Intent( mTopAction, mTopData != null ? Uri.parse(mTopData) : null); intent.setComponent(mTopComponent); if (mFactoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL) { intent.addCategory(Intent.CATEGORY_HOME); } ActivityInfo aInfo = intent.resolveActivityInfo(mContext.getPackageManager(), STOCK_PM_FLAGS); if (aInfo != null) { intent.setComponent(new ComponentName( aInfo.applicationInfo.packageName, aInfo.name)); // Don't do this if the home app is currently being // instrumented. ProcessRecord app = getProcessRecordLocked(aInfo.processName, aInfo.applicationInfo.uid); if (app == null || app.instrumentationClass == null) { intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK); mMainStack.startActivityLocked(null, intent, null, null, 0, aInfo, null, null, 0, 0, 0, false, false); } } return true; } ...... }

在这个函数中，可以看到AMS会创建一个intent实例，并且设置其category为HOME。而category为Home当然就是Home程序的启动Activity。接下来通过resolveActivityInfo向PackageManagerService查询对应的Activity，当然就是Home程序的Activity了。接下来通过mMainStack.startActivityLocked就启动了Home程序。

3.Launcher.onCreate

public final class Launcher extends Activity implements View.OnClickListener, OnLongClickListener, LauncherModel.Callbacks, AllAppsView.Watcher { ...... @Override protected void onCreate(Bundle savedInstanceState) { ...... if (!mRestoring) { mModel.startLoader(this, true); } ...... } ...... } public class LauncherModel extends BroadcastReceiver { ...... public void startLoader(Context context, boolean isLaunching) { ...... synchronized (mLock) { ...... // Don't bother to start the thread if we know it's not going to do anything if (mCallbacks != null && mCallbacks.get() != null) { // If there is already one running, tell it to stop. LoaderTask oldTask = mLoaderTask; if (oldTask != null) { if (oldTask.isLaunching()) { // don't downgrade isLaunching if we're already running isLaunching = true; } oldTask.stopLocked(); } mLoaderTask = new LoaderTask(context, isLaunching); sWorker.post(mLoaderTask); } } } ...... }

通过上面两段代码可以发现，在Launcher的onCreate初始化函数中，通过mModel来加载Loader，这里的mModel是一个LauncherModel类型的成员变量。 这里不是直接加载应用程序，而是把加载应用程序的操作作为一个消息来处理。这里的sWorker是一个Handler，通过它的post方式把一个消息放在消息队列中去，然后系统就会调用传进去的参数mLoaderTask的run函数来处理这个消息，这个mLoaderTask是LoaderTask类型的实例，于是，下面就会执行LoaderTask类的run函数了。

4.LoaderTask.loadAllAppsByBatch

在LoaderTask的run函数会调用loadAndBindAllApps,而在这个函数中又会调用loadAllAppsByBatch,所以真正启动各个app的工作是在这个函数中执行的。

public class LauncherModel extends BroadcastReceiver { ...... private class LoaderTask implements Runnable { ...... private void loadAllAppsByBatch() { ...... final Intent mainIntent = new Intent(Intent.ACTION_MAIN, null); mainIntent.addCategory(Intent.CATEGORY_LAUNCHER); final PackageManager packageManager = mContext.getPackageManager(); List<ResolveInfo> apps = null; int N = Integer.MAX_VALUE; int startIndex; int i=0; int batchSize = -1; while (i < N && !mStopped) { if (i == 0) { mAllAppsList.clear(); ...... apps = packageManager.queryIntentActivities(mainIntent, 0); ...... N = apps.size(); ...... if (mBatchSize == 0) { batchSize = N; } else { batchSize = mBatchSize; } ...... Collections.sort(apps, new ResolveInfo.DisplayNameComparator(packageManager)); } startIndex = i; for (int j=0; i<N && j<batchSize; j++) { // This builds the icon bitmaps. mAllAppsList.add(new ApplicationInfo(apps.get(i), mIconCache)); i++; } final boolean first = i <= batchSize; final Callbacks callbacks = tryGetCallbacks(oldCallbacks); final ArrayList<ApplicationInfo> added = mAllAppsList.added; mAllAppsList.added = new ArrayList<ApplicationInfo>(); mHandler.post(new Runnable() { public void run() { final long t = SystemClock.uptimeMillis(); if (callbacks != null) { if (first) { callbacks.bindAllApplications(added); } else { callbacks.bindAppsAdded(added); } ...... } else { ...... } } }); ...... } ...... } ...... } ...... }

函数首先构造一个CATEGORY_LAUNCHER类型的Intent,接着从mContext变量中获得PackageManagerService的接口。下一步就是通过这个PackageManagerService.queryIntentActivities接口来取回所有Action类型为Intent.ACTION_MAIN，并且Category类型为Intent.CATEGORY_LAUNCHER的Activity了。从queryIntentActivities函数调用处返回所要求的Activity后，便调用函数tryGetCallbacks(oldCallbacks)得到一个返CallBack接口，这个接口是由Launcher类实现的，接着调用这个接口的.bindAllApplications函数来进一步操作。注意，这里又是通过消息来处理加载应用程序的操作的。

5.Launcher.bindAllApplications

public final class Launcher extends Activity implements View.OnClickListener, OnLongClickListener, LauncherModel.Callbacks, AllAppsView.Watcher { ...... private AllAppsView mAllAppsGrid; ...... public void bindAllApplications(ArrayList<ApplicationInfo> apps) { mAllAppsGrid.setApps(apps); } ...... }

函数很简单，就是调用了mAllAppsGrid.setApps(apps)。这里的mAllAppsGrid是一个AllAppsView类型的变量，它的实际类型一般就是AllApps2D了。所以这个函数的作用很清晰了，就是在Home界面绘制各个应用的图标。具体的绘制逻辑这里就不多讲了。 到这里Home应用程序的启动过程就介绍完了。虽然函数的调用过程比较复杂，但其实总的逻辑还是比较简单的:

创建ActivityManagerService；ActivityManagerService通过mMainStack来启动Home程序mMainStack向PackageManagerService查询Home程序的Activity，然后启动该Activity，并放入该mMainStack中Home程序启动后通过PackageManagerService查询所有应用程序的启动ActivityHome程序在初始化的时候绘制Home界面当点击某个应用程序图标的时候，启动对应应用程序的启动Activity 相关资源：ACS-home程序