i want to make a notification when my position is near to a pin xamarin

i want to make a notification when my position is near to a pin xamarin.
and i have tried .

foreach (Pins a in listpin)
             {
                 double d = Location.CalculateDistance(a.Positionlat, a.Positionlon, MyLocation().Result, DistanceUnits.Kilometers);
                 DisplayAlert("Alert", $"{d}", "OK");
                 if (d < 1)
                 {
                     SendNotification();
                 }
             }

when i run the app the screen stays white and the display alert don’t work please help.

Source: Xamarin.ios Questions