关于android 7.2获取顶层应用的问题

目前试了三种方法，由于21版本之前的sdk好多接口废弃了，在android7.2上getRunningTasks的方法和getRunningAppProcesses的方法都不太起作用。试到最后一种才生效。

private String focusedPackage(){
        Log.d(TAG, "focusedPackage");
        ActivityManager am = (ActivityManager) mContext.getSystemService(mContext.ACTIVITY_SERVICE);
        List<ActivityManager.RunningTaskInfo> runningTaskInfos = am.getRunningTasks(6);
        if(runningTaskInfos==null||runningTaskInfos.size()<=0){
            Log.e(TAG,"focusedPackage falied for unknown package runningTaskInfos==null");
            return null;
        }
        ComponentName cn = runningTaskInfos.get(0).topActivity;
        if(cn==null){
            Log.e(TAG,"focusedPackage falied for unknown package cn==null");
            return null;
        }
        Log.e(TAG,"focusedPackage getPackageName here" + cn.getPackageName());
        return cn.getPackageName();
    }

    public static class TopActivityInfo {
        public String packageName = "";
        public String topActivityName = "";
    }

    private TopActivityInfo getTopActivityInfo() {
        Log.e(TAG,"focusedPackage getTopActivityInfo here");
        ActivityManager manager = ((ActivityManager)mContext.getSystemService(mContext.ACTIVITY_SERVICE));
        TopActivityInfo info = new TopActivityInfo();
        if (Build.VERSION.SDK_INT >= 21) {
            List<ActivityManager.RunningAppProcessInfo> pis = manager.getRunningAppProcesses();
            ActivityManager.RunningAppProcessInfo topAppProcess = pis.get(0);
            if (topAppProcess != null && topAppProcess.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND) {
                info.packageName = topAppProcess.processName;
                info.topActivityName = "";
                Log.e(TAG,"focusedPackage info.packageName here 22" + info.packageName);
            }
        } else {
            //getRunningTasks() is deprecated since API Level 21 (Android 5.0)
            List localList = manager.getRunningTasks(1);
            ActivityManager.RunningTaskInfo localRunningTaskInfo = (ActivityManager.RunningTaskInfo)localList.get(0);
            info.packageName = localRunningTaskInfo.topActivity.getPackageName();
            info.topActivityName = localRunningTaskInfo.topActivity.getClassName();
            Log.e(TAG,"focusedPackage info.packageName here 21" + info.packageName);
        }
        return info;
    }

虽然getRecentTasks在android studio中显示也在21之后的版本被废弃掉了，但是在target版本为25上还是实测起作用的。

    private boolean isSettingTop(){
        ActivityManager activityManager = (ActivityManager)mContext.getSystemService(Context.ACTIVITY_SERVICE);
        assert activityManager != null;
        String topPackage = activityManager.getRecentTasks(1,activityManager.RECENT_IGNORE_UNAVAILABLE).get(0).topActivity.getPackageName();
        Log.e(TAG,"focusedPackage isSettingTop" + topPackage);
        return SETTINGSNAME.equalsIgnoreCase(topPackage);
    }