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：
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。
