i'm creating a windows phone app ,where i've put a button to pin the app to start screen , but when press and hold the app icon on application list screen i find that the pin to start option can be used

ShellTile TileToFind = ShellTile.ActiveTiles.FirstOrDefault(x => x.NavigationUri.ToString().Contains("MainPage.xaml"));

        // Create the Tile if we didn't find that it already exists.
        if (TileToFind == null)
        {
            // Create the Tile object and set some initial properties for the Tile.
            // The Count value of 12 shows the number 12 on the front of the Tile. Valid values are 1-99.
            // A Count value of 0 indicates that the Count should not be displayed.
            StandardTileData NewTileData = new StandardTileData
            {
                BackgroundImage = new Uri("300.png", UriKind.Relative),
                Title = "apptitle",

                BackTitle = "title",
                BackContent = "testing ",
                BackBackgroundImage = null
            };

            // Create the Tile and pin it to Start. This will cause a navigation to Start and a deactivation of our app.
            ShellTile.Create(new Uri("/MainPage.xaml", UriKind.Relative), NewTileData);
        }
        else {
            MessageBox.Show("Already Pinned");
        }

how can i disable the user from pinning the application again from application list screen