private async void processPowerBtn_Clicked(object sender, EventArgs e) { TapiHandle handle = Globals.handleModem0; try { handle.NotificationChanged += Handle_NotiPowerStatusChanged; handle.RegisterNotiEvent(Notification.ModemPower); Log.Debug(Globals.LogTag, "Modem powercommand call start"); await modem.ProcessPowerCommand(PhonePowerCommand.Off); Log.Debug(Globals.LogTag, "Modem powercommand call off success"); } catch (Exception ex) { Log.Debug(Globals.LogTag, "Modem processpower command ,exception = " + ex.ToString()); } finally { handle.DeregisterNotiEvent(Notification.ModemPower); handle.NotificationChanged -= Handle_NotiPowerStatusChanged; } }