在Android10.0上，Recents功能分布在SystemUI和Launcher3里面集成.

一.初始化

跟Android8.1类似，先看初始化入口：

1.Recents.java

Recents继承SystemUI，进程启动后会在Dependency里面通过@Inject进行初始化，然后在SystemUIService里面调用SystemUIApplication的startServicesIfNeeded()里面进行启动：

private final RecentsImplementation mImpl
@Override
public void start() {
    //加入callback
    mCommandQueue.addCallback(this);
    mImpl.onStart(mContext);
}

RecentsImplementation替代了之前的RecentsImpl，是一个interface，由其实现类OverviewProxyRecentsImpl来执行操作，关于该类的实例化用到了dagger2，不懂的同学可以去学习一下；

2.OverviewProxyRecentsImpl.java

private OverviewProxyService mOverviewProxyService;
@Override
public void onStart(Context context) {
   
    mOverviewProxyService = Dependency.get(OverviewProxyService.class);
}

根据调用关系，在onStart()里面创建了OverviewProxyService对象，看一下具体实现：

3.OverviewProxyService.java

中间类，在该类内部去绑定远端的service：

@Inject
public OverviewProxyService(Context context, CommandQueue commandQueue,
            NavigationBarController navBarController, NavigationModeController navModeController,
            NotificationShadeWindowController statusBarWinController, SysUiState sysUiState,
            PipUI pipUI, Optional<Divider> dividerOptional,
            Optional<Lazy<StatusBar>> statusBarOptionalLazy,
            BroadcastDispatcher broadcastDispatcher) {
    super(broadcastDispatcher);

    mRecentsComponentName = ComponentName.unflattenFromString(context.getString(
            com.android.internal.R.string.config_recentsComponentName));
    mQuickStepIntent = new Intent(ACTION_QUICKSTEP)
            .setPackage(mRecentsComponentName.getPackageName());

   

    // Connect to the service
    updateEnabledState();
    startConnectionToCurrentUser();
}

public void startConnectionToCurrentUser() {
    if (mHandler.getLooper() != Looper.myLooper()) {
        mHandler.post(mConnectionRunnable);
    } else {
        internalConnectToCurrentUser();
    }
}

private void internalConnectToCurrentUser() {
    
    Intent launcherServiceIntent = new Intent(ACTION_QUICKSTEP)
                .setPackage(mRecentsComponentName.getPackageName());
    try {
        mBound = mContext.bindServiceAsUser(launcherServiceIntent,
                    mOverviewServiceConnection,
                    Context.BIND_AUTO_CREATE | Context.BIND_FOREGROUND_SERVICE_WHILE_AWAKE,
                    UserHandle.of(getCurrentUserId()));
        }
    
}

private IOverviewProxy mOverviewProxy;
private final ServiceConnection mOverviewServiceConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
      
        mOverviewProxy = IOverviewProxy.Stub.asInterface(service);
       
    }
}

跟随调用关系来看，在构造方法内部，会去执行startConnectionToCurrentUser来调用bindServiceAsUser()去启动service，在onServiceConnected中，通过IOverviewProxy.Stub.asInterface(service)来获取IOverviewProxy实例，后续会用到；
Service对应的Intent为android.intent.action.QUICKSTEP_SERVICE，R.string.config_recentsComponentName对应如下，用来获取远端服务的应用包名：

<string name="config_recentsComponentName" translatable="false"
        >com.android.launcher3/com.android.quickstep.RecentsActivity</string>

从ComponentName可以看到，被bind的service是在Launcher3里面，接下来一起看一下对应的远端Service；

4.TouchInteractionService.java

Launcher3内的入口类，通过该类来调用相关逻辑：

private final IBinder mMyBinder = new IOverviewProxy.Stub() {
   
    @BinderThread
    @Override
    public void onOverviewToggle() {
        mOverviewCommandHelper.onOverviewToggle();
    }
   
}

@Override
public IBinder onBind(Intent intent) {
    return mMyBinder;
}

可以看到，TouchInteractionService里面创建了IOverviewProxy.Stub实例，然后在onBind()返回；
TouchInteractionService是一个Service，在onCreate()里面进行了一些初始化相关的调用：

@Override
public void onCreate() {
    super.onCreate();
   
    mDeviceState.runOnUserUnlocked(this::onUserUnlocked);
   

    sConnected = true;
}

@UiThread
public void onUserUnlocked() {
   
    mOverviewComponentObserver = new OverviewComponentObserver(this, mDeviceState);
    mOverviewCommandHelper = new OverviewCommandHelper(this, mDeviceState,
                mOverviewComponentObserver);
   
}

可以看到，在TouchInteractionService启动后，会创建OverviewComponentObserver实例和OverviewCommandHelper实例，一起看一下这两个类的实现：

5.OverviewComponentObserver.java

public OverviewComponentObserver(Context context, RecentsAnimationDeviceState deviceState) {
    
    ComponentName fallbackComponent = new ComponentName(mContext, RecentsActivity.class);
    mFallbackIntent = new Intent(Intent.ACTION_MAIN)
                .addCategory(Intent.CATEGORY_DEFAULT)
                .setComponent(fallbackComponent)
                .setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    
    updateOverviewTargets();
}

可以看到，在构造方法内部会创建mFallbackIntent，从组成来看，通过该Intent启动RecentsActivity；接下来看一下 updateOverviewTargets()：

private void updateOverviewTargets() {
   
    mActivityInterface = FallbackActivityInterface.INSTANCE;
    mIsHomeAndOverviewSame = false;
    mOverviewIntent = mFallbackIntent;
   
}

在该方法内部，会将mFallbackIntent赋值给mOverviewIntent，后续启动Recents会用到mOverviewIntent；

6.OverviewCommandHelper.java

启动Recents的直接入口类，最终实现了onOverviewToggle()：

public OverviewCommandHelper(Context context, RecentsAnimationDeviceState deviceState,
            OverviewComponentObserver observer) {
    
    mRecentsModel = RecentsModel.INSTANCE.get(mContext);
    mOverviewComponentObserver = observer;
}

@BinderThread
public void onOverviewToggle() {
   
    ActivityManagerWrapper.getInstance()
                .closeSystemWindows(CLOSE_SYSTEM_WINDOWS_REASON_RECENTS);
    MAIN_EXECUTOR.execute(new RecentsActivityCommand<>());
}

以上就是Recents功能在初始化过程中涉及到的关键类，用一张流程图总结一下：

image

二.启动

前面分析了初始化涉及到的关键类，系统启动后会启动SystemUI进程，然后进行一系列初始化，接下来看一下进入Recents的流程：
关于手势或Key按键触发这一块逻辑处理跟Android8.1处理是一样的，入口都是在PhoneWindowManager，咱们从Recents接收toggleRecentApps()分析：

1.Recents.java

@Override
public void toggleRecentApps() {
   
    mImpl.toggleRecentApps();
}

2.OverviewProxyRecentsImpl.java

@Override
public void toggleRecentApps() {
    // If connected to launcher service, let it handle the toggle logic
    IOverviewProxy overviewProxy = mOverviewProxyService.getProxy();
    if (overviewProxy != null) {
        final Runnable toggleRecents = () -> {
            try {
                if (mOverviewProxyService.getProxy() != null) {
                    mOverviewProxyService.getProxy().onOverviewToggle();
                    mOverviewProxyService.notifyToggleRecentApps();
                }
            } catch (RemoteException e) {
                Log.e(TAG, "Cannot send toggle recents through proxy service.", e);
            }
        };
        //启动runnable
    }
}

在runnable内部会通过OverviewProxyService的getProxy()来获取到Launcher3端实现的IOveriewProxy对象引用，然后调用onOverviewToggle()方法：

3.TouchInteractionService.java

@BinderThread
@Override
public void onOverviewToggle() {
    mOverviewCommandHelper.onOverviewToggle();
}

4.OverviewCommandHelper.java

@BinderThread
public void onOverviewToggle() {

   ActivityManagerWrapper.getInstance()
                .closeSystemWindows(CLOSE_SYSTEM_WINDOWS_REASON_RECENTS);
   MAIN_EXECUTOR.execute(new RecentsActivityCommand<>());
}

可以看到，在执行onOverviewToggle()后，实际上是通过Executoe执行了RecentsActivityCommand：

private class RecentsActivityCommand<T extends StatefulActivity<?>> implements Runnable {
  
    public RecentsActivityCommand() {
        mActivityInterface = mOverviewComponentObserver.getActivityInterface();
      

        //预加载，Android8.1也有相同的逻辑
        mRecentsModel.getTasks(null);
    }

    @Override
     public void run() {
         
         // Otherwise, start overview.
         mListener = mActivityInterface.createActivityInitListener(this::onActivityReady);
         mListener.registerAndStartActivity(mOverviewComponentObserver.getOverviewIntent(),
                    new RemoteAnimationProvider() {
                        @Override
                        public AnimatorSet createWindowAnimation(
                                RemoteAnimationTargetCompat[] appTargets,
                                RemoteAnimationTargetCompat[] wallpaperTargets) {
                            return RecentsActivityCommand.this.createWindowAnimation(appTargets,
                                    wallpaperTargets);
                        }
                    }, mContext, MAIN_EXECUTOR.getHandler(),
                    mAnimationProvider.getRecentsLaunchDuration());
        }

可以看到，最终是通过registerAndStartActivity()来启动了intent，前面分析到mOverviewComponentObserver.getOverviewIntent()对应的就是mFallbackIntent，最终启动了RecentsActivity；
用一张流程图总结一下：

image

三.显示

在启动RecentsActivity后，会显示最近任务列表，看一下具体工作流程：

1.RecentsActivity.java

Recents显示Activity

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
  
    setupViews();
   
}

protected void setupViews() {
    inflateRootView(R.layout.fallback_recents_activity);
    setContentView(getRootView());
    mDragLayer = findViewById(R.id.drag_layer);
    mFallbackRecentsView = findViewById(R.id.overview_panel);
    mActionsView = findViewById(R.id.overview_actions_view);

    mDragLayer.recreateControllers();
    mFallbackRecentsView.init(mActionsView);
}

RecentsActivity继承了StatefulActivity，有些方法实现是在父类里面执行的，在onCreate()里面执行setupViews()，初始化了FallbackRecentsView，FallbackRecentsView继承了RecentsView，主要逻辑都是在RecentsView里面实现的，直接看RecentsView的实现逻辑：

2.RecentsView.java

Recents显示主View

public RecentsView(Context context, AttributeSet attrs, int defStyleAttr,
            BaseActivityInterface sizeStrategy) {
    super(context, attrs, defStyleAttr);
    
    mModel = RecentsModel.INSTANCE.get(context);

    mClearAllButton = (ClearAllButton) LayoutInflater.from(context)
                .inflate(R.layout.overview_clear_all_button, this, false);
    mClearAllButton.setOnClickListener(this::dismissAllTasks);
    mTaskViewPool = new ViewPool<>(context, this, R.layout.task, 20 /* max size */,
                10 /* initial size */);

   
}

可以看到，在构造方法内部，获取了RecentsModel实例，创建了ViewPool实例mTaskViewPool，该mTaskViewPool存储TaskView，对应的layout为 R.layout.task，最大数量为20；

@Override
protected void onAttachedToWindow() {
    super.onAttachedToWindow();
    updateTaskStackListenerState();
    ActivityManagerWrapper.getInstance().registerTaskStackListener(mTaskStackListener);
    //当snapshot更新时，会进行回调刷新UI
    RecentsModel.INSTANCE.get(getContext()).addThumbnailChangeListener(this);
}

在RecentsView显示时会回调onAttachedToWindow()，在内部执行了updateTaskStackListenerState()，然后做了一些注册回调操作，当有变化时，会进行回调通知来更新UI；

private void updateTaskStackListenerState() {
    boolean handleTaskStackChanges = mOverviewStateEnabled && isAttachedToWindow()
                && getWindowVisibility() == VISIBLE;
    if (handleTaskStackChanges != mHandleTaskStackChanges) {
        mHandleTaskStackChanges = handleTaskStackChanges;
        if (handleTaskStackChanges) {
            reloadIfNeeded();
        }
    }
}

在updateTaskStackListenerState()内部会进行一系列条件判断来确定是否执行reloadIfNeeded()，当首次进入时会执行reloadIfNeeded()：

public void reloadIfNeeded() {
    if (!mModel.isTaskListValid(mTaskListChangeId)) {
        mTaskListChangeId = mModel.getTasks(this::applyLoadPlan);
    }
}

通过RecentsModel的getTasks()来获取任务列表，然后回到applyLoadPlan()，getTasks()逻辑在后面进行分析，先看一下applyLoadPlan()方法的执行逻辑：

protected void applyLoadPlan(ArrayList<Task> tasks) {

    // Unload existing visible task data
    unloadVisibleTaskData();

    final int requiredTaskCount = tasks.size();
    if (getTaskViewCount() != requiredTaskCount) {
        for (int i = getTaskViewCount(); i < requiredTaskCount; i++) {
            addView(mTaskViewPool.getView());
        }
        if (requiredTaskCount > 0) {
            addView(mClearAllButton);
        }
    }

    // Rebind and reset all task views
    for (int i = requiredTaskCount - 1; i >= 0; i--) {
        final int pageIndex = requiredTaskCount - i - 1 + mTaskViewStartIndex;
        final Task task = tasks.get(i);
        final TaskView taskView = (TaskView) getChildAt(pageIndex);
        taskView.bind(task, mOrientationState);
    }
    resetTaskVisuals();
    }

在applyLoadPlan()内部，主要执行了四项工作：
  1. unloadVisibleTaskData()：将现有visible的task数据进行置空；
  2. 根据task数量(首次进入)进行addView，TaskView通过mTaskViewPool的getView()进行获取，最后添加clearAllButton；
  3. 对添加完的TaskView进行bind()操作，将对应的task存在TaskView内部，类似setTag()功能；
  4. 执行resetTaskVisuals()来刷新加载数据；

public void resetTaskVisuals() {
    // Update the set of visible task's data
    loadVisibleTaskData();
}

public void loadVisibleTaskData() {

    // Update the task data for the in/visible children
    for (int i = 0; i < getTaskViewCount(); i++) {
        TaskView taskView = getTaskViewAt(i);
        Task task = taskView.getTask();
         int index = indexOfChild(taskView);
         boolean visible = lower <= index && index <= upper;
         if (visible) {
             if (task == mTmpRunningTask) {
                // Skip loading if this is the task that we are animating into
                 continue;
             }
             if (!mHasVisibleTaskData.get(task.key.id)) {
                 taskView.onTaskListVisibilityChanged(true /* visible */);
             }
             mHasVisibleTaskData.put(task.key.id, visible);
         }
    }
}

最终在loadVisibleTaskData()里面通过TaskView的onTaskVisibilityChanged(true)来加载数据；

3.TaskView.java

Recents列表中Task对应的显示View

public void bind(Task task, RecentsOrientedState orientedState) {
    mTask = task;
    mSnapshotView.bind(task);
}

public void onTaskListVisibilityChanged(boolean visible) {
    if (mTask == null) {
        return;
    }
        cancelPendingLoadTasks();
    if (visible) {
        // These calls are no-ops if the data is already loaded, try and load the high
        // resolution thumbnail if the state permits
        RecentsModel model = RecentsModel.INSTANCE.get(getContext());
        TaskThumbnailCache thumbnailCache = model.getThumbnailCache();
        TaskIconCache iconCache = model.getIconCache();
        mThumbnailLoadRequest = thumbnailCache.updateThumbnailInBackground(
                    mTask, thumbnail -> mSnapshotView.setThumbnail(mTask, thumbnail));
        mIconLoadRequest = iconCache.updateIconInBackground(mTask,
                    (task) -> {
                        setIcon(task.icon);
                        if (ENABLE_QUICKSTEP_LIVE_TILE.get() && isRunningTask()) {
                            getRecentsView().updateLiveTileIcon(task.icon);
                        }
                        mDigitalWellBeingToast.initialize(mTask);
                    });
        } else {
            mSnapshotView.setThumbnail(null, null);
            setIcon(null);
            // Reset the task thumbnail reference as well (it will be fetched from the cache or
            // reloaded next time we need it)
            mTask.thumbnail = null;
        }
}

在onTaskListVisibilityChanged()内部，当visible为true时，执行mSnapshotView.setThumbnail()和setIcon()分别来加载缩略图和icon；当visible为false时，将其置空；

public TaskView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    setOnClickListener((view) -> {
         if (getTask() == null) {
             return;
         }
         launchTask(true /* animate */);
        });
}

public void launchTask(boolean animate) {
    launchTask(animate, false /* freezeTaskList */);
}

private void launchTaskInternal(boolean animate, boolean freezeTaskList,
            Consumer<Boolean> resultCallback, Handler resultCallbackHandler) {
    if (mTask != null) {
        ActivityManagerWrapper.getInstance().startActivityFromRecentsAsync(mTask.key,
                    opts, resultCallback, resultCallbackHandler);
        getRecentsView().onTaskLaunched(mTask);
    }
}

在TaskView内部设置了点击事件监听，当点击后会执行launchTask，最终会调用到ActivityManagerWrapper的startActivityFromRecentsAsync()来快速切换到对应的任务；

4.RecentsModel.java

Recents数据获取功能管理类

private RecentsModel(Context context) {
    mContext = context;
    mTaskList = new RecentTasksList(MAIN_EXECUTOR,
                new KeyguardManagerCompat(context), ActivityManagerWrapper.getInstance());
    mIconCache = new TaskIconCache(context, looper);
    mThumbnailCache = new TaskThumbnailCache(context, looper);

   ActivityManagerWrapper.getInstance().registerTaskStackListener(this);
}

   RecentsModel继承了TaskStackChangeListener，在构造方法内部初始化了RecentsTaskList、TaskIconCache和TaskThumbnailCache实例，注册了registerTaskStackListener回调；分别来获取最近任务列表、获取Task对应的Icon和，
   RecentsTaskList：获取最近任务列表；
   TaskIconCache：获取Task对应的icon，并进行缓存；
   TaskThumbnailCache：获取Task对应的thumbnailData，并进行缓存；
   与Android8.1不同的是，8.1上在获取最近任务列表后会获取任务对应的Thumbnail和Icon，最终封装成Task，在显示时直接通过Task.thumbnail和Task.icon就可以直接显示；11上会通过TaskIconCache和TaskThumbnailCache进行分别存储管理，首次显示或有新的任务，需要通过TaskIconCache和TaskThumbnailCache执行对应的request去获取并进行cache存储；

public int getTasks(Consumer<ArrayList<Task>> callback) {
    return mTaskList.getTasks(false /* loadKeysOnly */, callback);
}

执行getTasks时，实际是通过RecentsTaskList的getTasks()来执行的；

@Override
public void onTaskSnapshotChanged(int taskId, ThumbnailData snapshot) {
    mThumbnailCache.updateTaskSnapShot(taskId, snapshot);

    for (int i = mThumbnailChangeListeners.size() - 1; i >= 0; i--) {
        Task task = mThumbnailChangeListeners.get(i).onTaskThumbnailChanged(taskId, snapshot);
        if (task != null) {
            task.thumbnail = snapshot;
        }
    }
}

   当Task的snapshot截取完毕后，会收到onTaskSnapshotChanged()回调，先对snapshot进行缓存，然后执行onTaskThumbnailChanged()通知，在RecentsView里面对thumbnail进行更新；

5.RecentsTaskList.java

获取最近任务列表类

public synchronized int getTasks(boolean loadKeysOnly, Consumer<ArrayList<Task>> callback) {

    // Kick off task loading in the background
    UI_HELPER_EXECUTOR.execute(() -> {
       if (!mResultsBg.isValidForRequest(requestLoadId, loadKeysOnly)) {
            mResultsBg = loadTasksInBackground(Integer.MAX_VALUE, requestLoadId, loadKeysOnly);
       }
       TaskLoadResult loadResult = mResultsBg;
       mMainThreadExecutor.execute(() -> {
           mResultsUi = loadResult;
           if (callback != null) {
               ArrayList<Task> result = copyOf(mResultsUi);
               callback.accept(result);
           }
      });
    });

   return requestLoadId;
}

在getTasks()内部通过loadTasksInBackgroud()来获取TaskLoadResult对象mResultsBg，然后在主线程里面进行回调，最终执行到RecentsView里面的applyLoadPlan()是在主线程里面刷新UI；先看一下loadTasksInBackground()方法：

TaskLoadResult loadTasksInBackground(int numTasks, int requestId, boolean loadKeysOnly) {
    int currentUserId = Process.myUserHandle().getIdentifier();
    List<ActivityManager.RecentTaskInfo> rawTasks =
                mActivityManagerWrapper.getRecentTasks(numTasks, currentUserId);
    // The raw tasks are given in most-recent to least-recent order, we need to reverse it
    Collections.reverse(rawTasks);


    TaskLoadResult allTasks = new TaskLoadResult(requestId, loadKeysOnly, rawTasks.size());
    for (ActivityManager.RecentTaskInfo rawTask : rawTasks) {
        Task.TaskKey taskKey = new Task.TaskKey(rawTask);
        Task task;
        if (!loadKeysOnly) {
            boolean isLocked = tmpLockedUsers.get(taskKey.userId);
            task = Task.from(taskKey, rawTask, isLocked);
        } else {
            task = new Task(taskKey);
        }
        allTasks.add(task);
    }

    return allTasks;
}

可以看到，在loadTasksInBackgroud()内部，通过ActivityManagerWrapper的getRecentTasks()来获取rawTasks，然后反向排序，最后将其处理添加到allTasks，然后返回结果；

6.ActivityManagerWrapper.java

SystemUI与SystemServer交互类

public List<RecentTaskInfo> getRecentTasks(int numTasks, int userId) {
    try {
       return ActivityTaskManager.getService().getRecentTasks(numTasks,RECENT_IGNORE_UNAVAILABLE, userId).getList();
    }
}

public @NonNull ThumbnailData getTaskThumbnail(int taskId, boolean isLowResolution) {
    ActivityManager.TaskSnapshot snapshot = null;
    try {
        snapshot = ActivityTaskManager.getService().getTaskSnapshot(taskId, isLowResolution);
    } catch (RemoteException e) {
        Log.w(TAG, "Failed to retrieve task snapshot", e);
    }
    if (snapshot != null) {
        return new ThumbnailData(snapshot);
    } else {
        return new ThumbnailData();
    }
}

public boolean startActivityFromRecents(int taskId, ActivityOptions options) {
    try {
        Bundle optsBundle = options == null ? null : options.toBundle();
        ActivityTaskManager.getService().startActivityFromRecents(taskId, optsBundle);
        return true;
    } catch (Exception e) {
        return false;
    }
 }

ActivityManagerWrapper提供了跟systemserver交互的接口，相当于Android8.1中的SystemServicesProxy功能；
  用一张流程图总结显示过程：

image

以上就是对Android10.0 Recents功能的分析，功能实现由之前一个进程拆分到两个进程，其他处理基本上保持一致。

原作者：雷涛赛文