GET_TASKS权限在5.0已废弃；可以通过如下方式获取任务栈列表

Android任务栈.java

Log.e("Live",getTaskId()+"");
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.M) {
    ActivityManager activityManager = getSystemService(ActivityManager.class);
    //获取任务栈列表
    List<ActivityManager.AppTask> tasks = activityManager.getAppTasks();
    for (ActivityManager.AppTask task : tasks) {
        ActivityManager.RecentTaskInfo info = task.getTaskInfo();
        int activityCount = info.numActivities; //栈内Activity数量
        String topActivity = info.topActivity.getClassName(); //栈顶Activity
        String baseActivity = info.baseActivity.getClassName(); //栈底Activity
        Log.e("Live",activityCount+";"+topActivity+";"+baseActivity+";"+info.affiliatedTaskId);
//                task.setExcludeFromRecents(true); //不显示在最近任务列表中
//                task.finishAndRemoveTask(); //销毁任务栈内全部Activity
    }
}