1、Launcher

Launcher作為Android系統(tǒng)的桌面涂身，它的作用有兩點(diǎn)：
作為Android系統(tǒng)的啟動器，用于啟動應(yīng)用程序搓蚪；
作為Android系統(tǒng)的桌面蛤售，用于顯示和管理應(yīng)用程序的快捷圖標(biāo)或者其它桌面組件；

2妒潭、Launcher進(jìn)程啟動流程

2.1悴能、SystemServer調(diào)用

在SystemServer進(jìn)程啟動之后，執(zhí)行其run()函數(shù)雳灾，在里面執(zhí)行了大量的配置設(shè)置操作漠酿，并且啟動了各種引導(dǎo)服務(wù)、核心服務(wù)以及其他服務(wù)等谎亩，包括AMS炒嘲、PMS、WMS匈庭、電量管理服務(wù)等一系列服務(wù)夫凸，以及創(chuàng)建主線程Looper，并循環(huán)等待消息阱持；
其中在啟動引導(dǎo)服務(wù)方法中夭拌，啟動了ActivityManagerService，并且在啟動其他服務(wù)的方法中衷咽，調(diào)用AMS的systemReady()方法啼止，Launcher進(jìn)程就是從這兒開始啟動的；

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啟動的時候兵罢，執(zhí)行startOtherServices()方法中献烦，里面調(diào)用了AMS的systemReady()方法，通過該方法來啟動Launcher卖词；

// 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巩那、AMS執(zhí)行

在AMS中執(zhí)行systemReady()方法吏夯，在其中執(zhí)行startHomeActivityLocked()方法，傳入當(dāng)前用戶ID即横；

public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {
  ...
  synchronized (this) {
    ...
    startHomeActivityLocked(currentUserId, "systemReady");
    ...
  }
  ...
}

2.2.1噪生、獲取Launcher的Intent

在startHomeActivityLocked()方法中，首先通過getHomeIntent()方法东囚，獲取到要啟動的HomeActivity的intent對象跺嗽，其中mTopAction默認(rèn)為INTENT.ACTION_MAIN，并添加CATEGORY_HOME的category標(biāo)志页藻；
得到Intent對象桨嫁，通過PackageManager去獲取對應(yīng)符合的Activity，獲取對應(yīng)的ActivityInfo份帐，并獲取對應(yīng)的進(jìn)程記錄璃吧，此時對應(yīng)的進(jìn)程還沒啟動，后面繼續(xù)執(zhí)行废境，為intent添加FLAG_ACTIVITY_NEW_TASK啟動參數(shù)畜挨，開啟新棧，隨后調(diào)用ActivityStartController類的startHomeActivity()方法去執(zhí)行啟動噩凹；

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巴元、啟動Launcher

在startHomeActivity()方法中，調(diào)用obtainStarter()方法獲取到一個ActivityStarter對象驮宴，setCallingUid()方法設(shè)置當(dāng)前調(diào)用的Uid=0务冕，然后執(zhí)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()方法中幻赚，mayWait默認(rèn)為false禀忆，執(zhí)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();
  }
}

這里進(jìn)入了Activity的啟動流程落恼，Launcher本身就是一個系統(tǒng)APP箩退，用于顯示桌面等，LauncherApp啟動之后會執(zhí)行其生命周期方法初始化桌面布局佳谦；

2.3戴涝、初始化桌面圖標(biāo)

2.3.1、執(zhí)行onCreate()方法

@Override
protected void onCreate(Bundle savedInstanceState) {
  ...
  LauncherAppState app = LauncherAppState.getInstance(this);
  ...
}

獲取LauncherAppState钻蔑，通過LauncherAppState的getInstance()方法獲取啥刻，該方法里面會判斷當(dāng)前線程是否為主線程，在主線程時還會直接new出對象咪笑，不在主線程時可帽，通過MainThreadExecutor的submit()方法向主線程提交一個任務(wù)去獲取該對象；

// 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窗怒、讀取安裝APP信息

在LauncherAppState的構(gòu)造方法中映跟，會新建InvariantDeviceProfile對象蓄拣，這個類主要是存儲App的基本配置信息，例如App圖標(biāo)的尺寸大小努隙，文字大小球恤，每個工作空間或文件夾能顯示多少App等；
在LauncherAppState的構(gòu)造方法中荸镊，會獲取WindowManager咽斧，并獲取屏幕的尺寸，解析桌面布局文件躬存，獲取默認(rèn)尺寸信息等张惹；

@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、注冊Intent廣播

新建LauncherModel對象优构，該對象是一個BroadcastReceiver，并添加App變化的回調(diào)雁竞，以及設(shè)置Filter并注冊廣播钦椭，用于監(jiān)聽桌面App的變化；

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碑诉、解析Launcher布局

繼續(xù)回到Launcher的onCreate()方法彪腔，將Launcher添加到LauncherModel中，是以弱引用的方式添加进栽，初始化一些其工作德挣，解析Launcher的布局，

2.3.5快毛、加載桌面

onCreate()方法中格嗅，通過LauncherModel的startLoader()來加載桌面App；

@Override
protected 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()方法中唠帝，新建了一個LoaderResults對象屯掖，并通過startLoaderForResults()方法創(chuàng)建出一個LoaderTask的Runnable任務(wù)，將其在工作線程中執(zhí)行起來襟衰；

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()方法中贴铜，去加載手機(jī)已安裝的App的信息，查詢數(shù)據(jù)庫獲取已安裝的App的相關(guān)信息瀑晒，加載Launcher布局绍坝，并將數(shù)據(jù)轉(zhuǎn)化為View，綁定到界面上苔悦，由此我們就可以看到桌面顯示的宮格列表的桌面圖標(biāo)了轩褐；

public void run() {
  ...
  try (LauncherModel.LoaderTransaction transaction = mApp.getModel().beginLoader(this)) {
    // 查詢數(shù)據(jù)庫整理App信息，轉(zhuǎn)化為View綁定到界面
    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);
}

來自：https://www.yuque.com/jesus_yangshijie/ruafsa/yl7sey