Assign the ItemsSource after InitializeComponent
public SelectProfile()
{
InitializeComponent();
ObservableCollection<Player> players = new ObservableCollection<Player>();
players.Add(new Player { FirstName = "Waseem" });
players.Add(new Player { FirstName = "Waseem2" });
players.Add(new Player { FirstName = "Waseem3" });
players.ItemsSource = players; // assigning data
}