Android判断应用是否是从后台回到前台

很久以前在网上找到的，今天无意间看到这段代码，有点忘记了，赶紧记录下来，以备日后查看。顺便感谢一下当时的大神

private void SetIsRunningForeground() 
{

    var packageName = this.PackageName;
    var activityManager = (ActivityManager)this.GetSystemService(Android.Content.Context.ActivityService);          
    var appProcesses = activityManager.RunningAppProcesses;

    bool flag = false;

    if (appProcesses != null) {
        foreach (var running in appProcesses) {
            if (running.ProcessName.Equals (packageName)) {
                var status = running.Importance;
                if (status == Importance.Visible || status == Importance.Foreground) {
                    flag = true;
                }
            }
        }
    }

    SharedPreferenceManager.SetIsRunningForeground (this, flag);
}   
可以在onStop里用handler在0.5s（也可以更短）之后调用这个方法，然后在onResume里取sharedPreference的值就知道是否是从后台回到前台的了。