The GeoCoordinate class (.NET Framework 4 and higher) already has GetDistanceTo method. var sCoord = new GeoCoordinate(sLatitude, sLongitude); var eCoord = new GeoCoordinate(eLatitude, eLongitude); return sCoord.GetDistanceTo(eCoord); The distance is in meters. You need to reference System.Device.
Most of the other answers here are somewhat out-of-date with today’s best practices. As such here is the application of using PBKDF2/Rfc2898DeriveBytes to store and verify passwords. The following code is in a stand-alone class in this post: Another example of how to store a salted password hash. The basics are really easy, so here … Read more
Have you looked at the ShareStatusTask :- http://msdn.microsoft.com/en-us/library/hh394027(v=VS.92).aspx
If your application is not running in the foreground you can’t catch tap-events. That’s basically the difference between background and foreground.