我们如何在活动堆栈android中获取活动的数量。

ActivityManager activityManager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
List<ActivityManager.RunningTaskInfo> runningTasks = activityManager.getRunningTasks(1);
int numActivities = runningTasks.get(0).numActivities;

ActivityManager activityManager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
List<ActivityManager.RunningAppProcessInfo> runningProcesses = activityManager.getRunningAppProcesses();
int numActivities = 0;
for (ActivityManager.RunningAppProcessInfo processInfo : runningProcesses) {
    if (processInfo.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND
            && processInfo.importanceReasonCode == ActivityManager.RunningAppProcessInfo.REASON_ACTIVITY_STACK) {
        numActivities = processInfo.pkgList.length;
        break;
    }
}