/**
     * Android判断应用是否在前台运行
     *      0：异常；1：前台；2：后台；3：未运行；
     */
    private int isFrontShow(Context context) {
        if (context == null) {
            return 0;
        }
        ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
        List<ActivityManager.RunningTaskInfo> runningTasks = activityManager.getRunningTasks(20);
        if (context.getPackageName().equals(runningTasks.get(0).topActivity.getPackageName())) {
            return 1;
        } else {
            for (ActivityManager.RunningTaskInfo runningTask : runningTasks) {
                if (context.getPackageName().equals(runningTask.topActivity.getPackageName())) {
                    return 2;
                }
            }
        }
        return 3;
    }