Previously in windowsphone 8.0,to determine screen resolutions we are using the "App.Current.Host.Content.ScaleFactor" .
But now its not working in windowsphone 8.1,So this post is explained about what is the alternative way for detecting screen resolutions in windowsphone store 8.1.
var scaleFactor = DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel;
string currentresolution = Window.Current.Bounds.Width * scaleFactor + "*" +
Window.Current.Bounds.Height * scaleFactor;
MessageDialog messageDialog = new MessageDialog(currentresolution);
await messageDialog.ShowAsync();