1、Launcher
Launcher作为Android体系的桌面，它的作用有两点：
作为Android体系的启动器，用于启动应用步伐；
作为Android体系的桌面，用于表现和管理应用步伐的快捷图标大概别的桌面组件；
2、Launcher进程启动流程
2.1、SystemServer调用
在SystemServer进程启动之后，实行其run()函数，在内里实行了大量的设置设置操纵，而且启动了各种引导服务、核心服务以及其他服务等，包罗AMS、PMS、WMS、电量管理服务等一系列服务，以及创建主线程Looper，并循环等待消息；
此中在启动引导服务方法中，启动了ActivityManagerService，而且在启动其他服务的方法中，调用AMS的systemReady()方法，Launcher进程就是从这儿开始启动的；
public final class SystemServer { private void run() { ... startBootstrapServices(); startOtherServices(); ... } private void startBootstrapServices() { ... mActivityManagerService = mSystemServiceManager.startService(ActivityManagerService.Lifecycle.class).getService(); mActivityManagerService.setSystemServiceManager(mSystemServiceManager); mActivityManagerService.setInstaller(installer); ... } private void startOtherServices() { ... mActivityManagerService.systemReady(() -> { }, BOOT_TIMINGS_TRACE_LOG); }}在SystemServer启动的时间，实行startOtherServices()方法中，内里调用了AMS的systemReady()方法，通过该方法来启动Launcher；
// Tag for timing measurement of main thread.private static final String SYSTEM_SERVER_TIMING_TAG = "SystemServerTiming";private static final TimingsTraceLog BOOT_TIMINGS_TRACE_LOG = new TimingsTraceLog(SYSTEM_SERVER_TIMING_TAG, Trace.TRACE_TAG_SYSTEM_SERVER);private void startOtherServices() { ... mActivityManagerService.systemReady(() -> { Slog.i(TAG, "Making services ready"); traceBeginAndSlog("StartActivityManagerReadyPhase"); mSystemServiceManager.startBootPhase(SystemService.PHASE_ACTIVITY_MANAGER_READY); ... }, BOOT_TIMINGS_TRACE_LOG);}2.2、AMS实行
在AMS中实行systemReady()方法，在此中实行startHomeActivityLocked()方法，传入当前用户ID；
public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) { ... synchronized (this) { ... startHomeActivityLocked(currentUserId, "systemReady"); ... } ...}2.2.1、获取Launcher的Intent
在startHomeActivityLocked()方法中，起首通过getHomeIntent()方法，获取到要启动的HomeActivity的intent对象，此中mTopAction默以为INTENT.ACTION_MAIN，并添加CATEGORY_HOME的category标记；
得到Intent对象，通过PackageManager去获取对应符合的Activity，获取对应的ActivityInfo，并获取对应的进程纪录，此时对应的进程还没启动，反面继续实行，为intent添加FLAG_ACTIVITY_NEW_TASK启动参数，开启新栈，随后调用ActivityStartController类的startHomeActivity()方法去实行启动；
boolean startHomeActivityLocked(int userId, String reason) { ... Intent intent = getHomeIntent(); ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId); if (aInfo != null) { intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name)); // Don't do this if the home app is currently being instrumented. 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() | FLAG_ACTIVITY_NEW_TASK); final int resolvedUserId = UserHandle.getUserId(aInfo.applicationInfo.uid); // For ANR debugging to verify if the user activity is the one that actually launched. final String myReason = reason + ":" + userId + ":" + resolvedUserId; mActivityStartController.startHomeActivity(intent, aInfo, myReason); } } ... return true;}Intent getHomeIntent() { Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null); intent.setComponent(mTopComponent); intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING); if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) { intent.addCategory(Intent.CATEGORY_HOME); } return intent;}2.2.2、启动Launcher
在startHomeActivity()方法中，调用obtainStarter()方法获取到一个ActivityStarter对象，setCallingUid()方法设置当前调用的Uid=0，然后实行其execute()方法；
void startHomeActivity(Intent intent, ActivityInfo aInfo, String reason) { mSupervisor.moveHomeStackTaskToTop(reason); mLastHomeActivityStartResult = obtainStarter(intent, "startHomeActivity: " + reason) .setOutActivity(tmpOutRecord) .setCallingUid(0) .setActivityInfo(aInfo) .execute(); mLastHomeActivityStartRecord = tmpOutRecord[0]; if (mSupervisor.inResumeTopActivity) { // If we are in resume section already, home activity will be initialized, but not // resumed (to avoid recursive resume) and will stay that way until something pokes it // again. We need to schedule another resume. mSupervisor.scheduleResumeTopActivities(); }}在ActivityStarter的execute()方法中，mayWait默以为false，实行startActivity()方法；
int execute() { try { // TODO(b/64750076): Look into passing request directly to these methods to allow // for transactional diffs and preprocessing. if (mRequest.mayWait) { return startActivityMayWait(mRequest.caller, mRequest.callingUid, ...); } else { return startActivity(mRequest.caller, mRequest.intent, mRequest.ephemeralIntent, ...); } } finally { onExecutionComplete(); }}这里进入了Activity的启动流程，Launcher自己就是一个体系APP，用于表现桌面等，LauncherApp启动之后会实行其生命周期方法初始化桌面结构；
2.3、初始化桌面图标
2.3.1、实行onCreate()方法
@Overrideprotected void onCreate(Bundle savedInstanceState) { ... LauncherAppState app = LauncherAppState.getInstance(this); ...}获取LauncherAppState，通过LauncherAppState的getInstance()方法获取，该方法内里会判断当前线程是否为主线程，在主线程时还会直接new出对象，不在主线程时，通过MainThreadExecutor的submit()方法向主线程提交一个任务去获取该对象；
// We do not need any synchronization for this variable as its only written on UI thread.private static LauncherAppState INSTANCE;public static LauncherAppState getInstance(final Context context) { if (INSTANCE == null) { if (Looper.myLooper() == Looper.getMainLooper()) { INSTANCE = new LauncherAppState(context.getApplicationContext()); } else { try { return new MainThreadExecutor().submit(new Callable<LauncherAppState>() { @Override public LauncherAppState call() throws Exception { return LauncherAppState.getInstance(context); } }).get(); } catch (InterruptedException|ExecutionException e) { throw new RuntimeException(e); } } } return INSTANCE;}2.3.2、读取安装APP信息
在LauncherAppState的构造方法中，会新建InvariantDeviceProfile对象，这个类紧张是存储App的根本设置信息，例如App图标的尺寸大小，笔墨大小，每个工作空间或文件夹能表现多少App等；
在LauncherAppState的构造方法中，会获取WindowManager，并获取屏幕的尺寸，分析桌面结构文件，获取默认尺寸信息等；
@TargetApi(23)public InvariantDeviceProfile(Context context) { WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE); Display display = wm.getDefaultDisplay(); DisplayMetrics dm = new DisplayMetrics(); display.getMetrics(dm); ... ArrayList<InvariantDeviceProfile> closestProfiles = findClosestDeviceProfiles(minWidthDps, minHeightDps, getPredefinedDeviceProfiles(context)); ...}ArrayList<InvariantDeviceProfile> getPredefinedDeviceProfiles(Context context) { ArrayList<InvariantDeviceProfile> profiles = new ArrayList<>(); try (XmlResourceParser parser = context.getResources().getXml(R.xml.device_profiles)) { final int depth = parser.getDepth(); int type; while (((type = parser.next()) != XmlPullParser.END_TAG || parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) { if ((type == XmlPullParser.START_TAG) && "profile".equals(parser.getName())) { TypedArray a = context.obtainStyledAttributes(Xml.asAttributeSet(parser), R.styleable.InvariantDeviceProfile); int numRows = a.getInt(R.styleable.InvariantDeviceProfile_numRows, 0); int numColumns = a.getInt(R.styleable.InvariantDeviceProfile_numColumns, 0); float iconSize = a.getFloat(R.styleable.InvariantDeviceProfile_iconSize, 0); profiles.add(new InvariantDeviceProfile( a.getString(R.styleable.InvariantDeviceProfile_name), a.getFloat(R.styleable.InvariantDeviceProfile_minWidthDps, 0), a.getFloat(R.styleable.InvariantDeviceProfile_minHeightDps, 0), numRows, numColumns, a.getInt(R.styleable.InvariantDeviceProfile_numFolderRows, numRows), a.getInt(R.styleable.InvariantDeviceProfile_numFolderColumns, numColumns), iconSize, a.getFloat(R.styleable.InvariantDeviceProfile_landscapeIconSize, iconSize), a.getFloat(R.styleable.InvariantDeviceProfile_iconTextSize, 0), a.getInt(R.styleable.InvariantDeviceProfile_numHotseatIcons, numColumns), a.getResourceId(R.styleable.InvariantDeviceProfile_defaultLayoutId, 0), a.getResourceId(R.styleable.InvariantDeviceProfile_demoModeLayoutId, 0))); a.recycle(); } } } catch (IOException|XmlPullParserException e) { throw new RuntimeException(e); } return profiles;}2.3.3、注册Intent广播
新建LauncherModel对象，该对象是一个BroadcastReceiver，并添加App变革的回调，以及设置Filter并注册广播，用于监听桌面App的变革；
private LauncherAppState(Context context) { ... mModel = new LauncherModel(this, mIconCache, AppFilter.newInstance(mContext)); LauncherAppsCompat.getInstance(mContext).addOnAppsChangedCallback(mModel); // Register intent receivers IntentFilter filter = new IntentFilter(); filter.addAction(Intent.ACTION_LOCALE_CHANGED); // For handling managed profiles filter.addAction(Intent.ACTION_MANAGED_PROFILE_ADDED); filter.addAction(Intent.ACTION_MANAGED_PROFILE_REMOVED); ... mContext.registerReceiver(mModel, filter); ...}public class LauncherModel extends BroadcastReceiver ... {}2.3.4、分析Launcher结构
继续回到Launcher的onCreate()方法，将Launcher添加到LauncherModel中，是以弱引用的方式添加，初始化一些其工作，分析Launcher的结构，
2.3.5、加载桌面
onCreate()方法中，通过LauncherModel的startLoader()来加载桌面App；
@Overrideprotected void onCreate(Bundle savedInstanceState) { ... if (!mModel.startLoader(currentScreen)) { if (!internalStateHandled) { // If we are not binding synchronously, show a fade in animation when // the first page bind completes. mDragLayer.getAlphaProperty(ALPHA_INDEX_LAUNCHER_LOAD).setValue(0); } } else { // Pages bound synchronously. mWorkspace.setCurrentPage(currentScreen); setWorkspaceLoading(true); } ...}在LauncherModel的startLoader()方法中，新建了一个LoaderResults对象，并通过startLoaderForResults()方法创建出一个LoaderTask的Runnable任务，将其在工作线程中实行起来；
public boolean startLoader(int synchronousBindPage) { ... 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) { ... LoaderResults loaderResults = new LoaderResults(mApp, sBgDataModel, mBgAllAppsList, synchronousBindPage, mCallbacks); if (mModelLoaded && !mIsLoaderTaskRunning) { ... return true; } else { startLoaderForResults(loaderResults); } } } return false;}public void startLoaderForResults(LoaderResults results) { synchronized (mLock) { stopLoader(); mLoaderTask = new LoaderTask(mApp, mBgAllAppsList, sBgDataModel, results); runOnWorkerThread(mLoaderTask); }}private static void runOnWorkerThread(Runnable r) { if (sWorkerThread.getThreadId() == Process.myTid()) { r.run(); } else { // If we are not on the worker thread, then post to the worker handler sWorker.post(r); }}在LoaderTask的run()方法中，去加载手机已安装的App的信息，查询数据库获取已安装的App的干系信息，加载Launcher结构，并将数据转化为View，绑定到界面上，由此我们就可以看到桌面表现的宫格列表的桌面图标了；
public void run() { ... try (LauncherModel.LoaderTransaction transaction = mApp.getModel().beginLoader(this)) { // 查询数据库整理App信息，转化为View绑定到界面 loadWorkspace(); mResults.bindWorkspace(); loadAllApps(); mResults.bindAllApps(); loadDeepShortcuts(); mResults.bindDeepShortcuts(); mBgDataModel.widgetsModel.update(mApp, null); mResults.bindWidgets(); transaction.commit(); } catch (CancellationException e) { // Loader stopped, ignore TraceHelper.partitionSection(TAG, "Cancelled"); } TraceHelper.endSection(TAG);}来自：https://www.yuque.com/jesus_yangshijie/ruafsa/yl7sey
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