在任务栏中清除掉播放器的进程，状态栏仍有音乐播放器状态，且音乐仍在后台播放

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在任务栏中清除掉播放器的进程，状态栏仍有音乐播放器状态，且音乐仍在后台播放

1.先从UI切入问题分析，使用Monitor—Hierarchy View找到清除任务X按钮对应的id为r.id.dismiss_task,并且属于SystemUI

2.到SystemUI定位到包含dismiss_task的是TaskViewHeader.java,该按钮对应的onClick事件为：

TaskView tv = Utilities.findParent(this, TaskView.class);
            tv.dismissTask();

            // Keep track of deletions by the dismiss button
            MetricsLogger.histogram(getContext(), "overview_task_dismissed_source",
                    Constants.Metrics.DismissSourceHeaderButton);

3.查看TaskView.java中的dismissTask

void dismissTask() {
        // Animate out the view and call the callback
        final TaskView tv = this;
        DismissTaskViewEvent dismissEvent = new DismissTaskViewEvent(tv);
        dismissEvent.addPostAnimationCallback(new Runnable() {
            @Override
            public void run() {
                EventBus.getDefault().send(new TaskViewDismissedEvent(mTask, tv,
                        new AnimationProps(TaskStackView.DEFAULT_SYNC_STACK_DURATION,
                                Interpolators.FAST_OUT_SLOW_IN)));
            }
        });
        EventBus.getDefault().send(dismissEvent);
    }

这里EventBus send一个DismissTaskViewEvent，处理完成会回调再发生一个TaskViewDismissedEvent

5.定位到处理DismissTaskViewEvent是在TaskStackView.java

    public final void onBusEvent(DismissTaskViewEvent event) {
        // For visible children, defer removing the task until after the animation
        mAnimationHelper.startDeleteTaskAnimation(
                event.taskView, useGridLayout(), event.getAnimationTrigger());
    }

处理TaskViewDismissedEvent

public final void onBusEvent(TaskViewDismissedEvent event) {
        // Announce for accessibility
        announceForAccessibility(getContext().getString(
                R.string.accessibility_recents_item_dismissed, event.task.title));

        if (useGridLayout() && event.animation != null) {
            event.animation.setListener(new AnimatorListenerAdapter() {
                public void onAnimationEnd(Animator animator) {
                    if (mTaskViewFocusFrame != null) {
                        // Resize the grid layout task view focus frame
                        mTaskViewFocusFrame.resize();
                    }
                }
            });
        }

        // Remove the task from the stack
        mStack.removeTask(event.task, event.animation, false /* fromDockGesture */);
        EventBus.getDefault().send(new DeleteTaskDataEvent(event.task));
        if (mStack.getTaskCount() > 0 && Recents.getConfiguration().isLowRamDevice) {
            EventBus.getDefault().send(new ShowStackActionButtonEvent(false /* translate */));
        }

        MetricsLogger.action(getContext(), MetricsEvent.OVERVIEW_DISMISS,
                event.task.key.getComponent().toString());
    }

6.接着DeleteTaskDataEvent在RecentsActivity.java处理

public final void onBusEvent(DeleteTaskDataEvent event) {
        // Remove any stored data from the loader
        RecentsTaskLoader loader = Recents.getTaskLoader();
        loader.deleteTaskData(event.task, false);

        // Remove the task from activity manager
        SystemServicesProxy ssp = Recents.getSystemServices();
        ssp.removeTask(event.task.key.id);
    }

7.SystemServicesProxy.java中removeTask

 /** Removes the task */
    public void removeTask(final int taskId) {
        if (mAm == null) return;
        if (RecentsDebugFlags.Static.EnableMockTasks) return;

        // Remove the task.
        mUiOffloadThread.submit(() -> {
            mAm.removeTask(taskId);
        });
    }

这里就是关键代码了，通过调用ActivityManager的removeTask来删除任务

8.通过ActivityManager.java其对应的是ActivityManagerService.java

    @Override
    public boolean removeTask(int taskId) {
        enforceCallingPermission(android.Manifest.permission.REMOVE_TASKS, "removeTask()");
        synchronized (this) {
            final long ident = Binder.clearCallingIdentity();
            try {
                return mStackSupervisor.removeTaskByIdLocked(taskId, true, REMOVE_FROM_RECENTS);
            } finally {
                Binder.restoreCallingIdentity(ident);
            }
        }
    }

9.ActivityStackSupervisor.java

    boolean removeTaskByIdLocked(int taskId, boolean killProcess, boolean removeFromRecents,
            boolean pauseImmediately) {
        final TaskRecord tr = anyTaskForIdLocked(taskId, MATCH_TASK_IN_STACKS_OR_RECENT_TASKS,
                INVALID_STACK_ID);
        if (tr != null) {
            tr.removeTaskActivitiesLocked(pauseImmediately);
            cleanUpRemovedTaskLocked(tr, killProcess, removeFromRecents);
            if (tr.isPersistable) {
                mService.notifyTaskPersisterLocked(null, true);
            }
            return true;
        }
        Slog.w(TAG, "Request to remove task ignored for non-existent task " + taskId);
        return false;
    }

 void cleanUpRemovedTaskLocked(TaskRecord tr, boolean killProcess, boolean removeFromRecents) {
        if (removeFromRecents) {
            mRecentTasks.remove(tr);
            tr.removedFromRecents();
        }
        ComponentName component = tr.getBaseIntent().getComponent();
        if (component == null) {
            Slog.w(TAG, "No component for base intent of task: " + tr);
            return;
        }

        // Find any running services associated with this app and stop if needed.
        mService.mServices.cleanUpRemovedTaskLocked(tr, component, new Intent(tr.getBaseIntent()));

        if (!killProcess) {
            return;
        }

        // Determine if the process(es) for this task should be killed.
        final String pkg = component.getPackageName();
        ArrayList procsToKill = new ArrayList<>();
        ArrayMap> pmap = mService.mProcessNames.getMap();
        for (int i = 0; i < pmap.size(); i++) {

            SparseArray uids = pmap.valueAt(i);
            for (int j = 0; j < uids.size(); j++) {
                ProcessRecord proc = uids.valueAt(j);
                if (proc.userId != tr.userId) {
                    // Don't kill process for a different user.
                    continue;
                }
                if (proc == mService.mHomeProcess) {
                    // Don't kill the home process along with tasks from the same package.
                    continue;
                }
                if (!proc.pkgList.containsKey(pkg)) {
                    // Don't kill process that is not associated with this task.
                    continue;
                }

                for (int k = 0; k < proc.activities.size(); k++) {
                    TaskRecord otherTask = proc.activities.get(k).getTask();
                    if (tr.taskId != otherTask.taskId && otherTask.inRecents) {
                        // Don't kill process(es) that has an activity in a different task that is
                        // also in recents.
                        return;
                    }
                }

                if (proc.foregroundServices) {
                    // Don't kill process(es) with foreground service.
                    return;
                }

                // Add process to kill list.
                procsToKill.add(proc);
            }
        }

        // Kill the running processes.
        for (int i = 0; i < procsToKill.size(); i++) {
            ProcessRecord pr = procsToKill.get(i);
            if (pr.setSchedGroup == ProcessList.SCHED_GROUP_BACKGROUND
                    && pr.curReceivers.isEmpty()) {
                pr.kill("remove task", true);
            } else {
                // We delay killing processes that are not in the background or running a receiver.
                pr.waitingToKill = "remove task";
            }
        }
    }

通过上述定位会发现music app包含了前台的服务foregroundServices，所以其process不会被kill掉。这个是google原生设计的。
那解决该问题，我们可以增加判断如果是removeFromRecents 为true时将其包含foregroundServices也kill掉