WakefulBroadcastReceiver Xamarin不起作用

Question

我写了一个程序，当收到短信时它会响起。但是它仅在程序运行时有效，而在程序关闭时则无效。

我该怎么办？

public class MainActivity : Activity
{
    SampleReceiver receiver;

    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);

        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.Main);

        receiver = new SampleReceiver();

        IntentFilter intentFilter = new IntentFilter("android.provider.Telephony.SMS_RECEIVED");
        intentFilter.Priority = 1000;

        RegisterReceiver(receiver, intentFilter);

        // Code omitted for clarity
    }


}

[BroadcastReceiver(Enabled = true, Exported = true)]
public class SampleReceiver : WakefulBroadcastReceiver
{

    private const string IntentAction = "android.provider.Telephony.SMS_RECEIVED";
    public override void OnReceive(Context context, Intent intent)
    {
        try
        {
            Android.Net.Uri uri = RingtoneManager.GetDefaultUri(RingtoneType.Ringtone);
            Ringtone ringtone = RingtoneManager.GetRingtone(context, uri);
            ringtone.Play();

            if (intent.HasExtra("pdus"))
            {
                var smsArray = (Java.Lang.Object[])intent.Extras.Get("pdus");

                foreach (var item in smsArray)
                {
                    var sms = SmsMessage.CreateFromPdu((byte[])item);
                    string address = sms.OriginatingAddress;
                    string smsText = sms.MessageBody;

                    Toast.MakeText(context, "Massage from : " + address + " Says : " + smsText, ToastLength.Long).Show();
                }
            }


        }
        catch (System.Exception ex)
        {
            //Toast.MakeText(context, ex.Message, ToastLength.Long).Show();
        }
    }
}

Tnx