核心类

Framework中有一个类SystemActivityMonitoringService专门用于监控Activity堆栈变化，属于隐藏Api，应用侧无法调用。此类位于

packages/services/Car/service/src/com/android/car/SystemActivityMonitoringService.java

方法

void registerTaskStackListener(in ITaskStackListener listener);

void registerProcessObserver(in IProcessObserver observer);

这两个方法都位于AMS中，不对应用开放

SystemActivityMonitoringService中init调用

    @Overridepublic void init() {// Monitoring both listeners are necessary as there are cases where one listener cannot// monitor activity change.try {mAm.registerProcessObserver(mProcessObserver);mAm.registerTaskStackListener(mTaskListener);} catch (RemoteException e) {Log.e(CarLog.TAG_AM, "cannot register activity monitoring", e);throw new RuntimeException(e);}updateTasks();}

 ProcessObserver

void onForegroundActivitiesChanged(int pid, int uid, boolean foregroundActivities) //前台Activity发生改变

void onForegroundServicesChanged(int pid, int uid, int fgServiceTypes) //前台服务发生变化

   private class ProcessObserver extends IProcessObserver.Stub {@Overridepublic void onForegroundActivitiesChanged(int pid, int uid, boolean foregroundActivities) {if (Log.isLoggable(CarLog.TAG_AM, Log.INFO)) {Log.i(CarLog.TAG_AM,String.format("onForegroundActivitiesChanged uid %d pid %d fg %b",uid, pid, foregroundActivities));}mHandler.requestForegroundActivitiesChanged(pid, uid, foregroundActivities);}@Overridepublic void onForegroundServicesChanged(int pid, int uid, int fgServiceTypes) {}@Overridepublic void onProcessDied(int pid, int uid) {mHandler.requestProcessDied(pid, uid);}}

TaskListener

onTaskCreated 应用被创建，首次被拉起至前台；

onTaskRemoved 应用进程被移除

onTaskMovedToFront 应用从后台切换至前台

    private class TaskListener extends TaskStackListener {@Overridepublic void onTaskStackChanged() {if (Log.isLoggable(CarLog.TAG_AM, Log.INFO)) {Log.i(CarLog.TAG_AM, "onTaskStackChanged");}mHandler.requestUpdatingTask();}}