private void Searchbar_TextChanged(object sender, TextChangedEventArgs e)
{
StudentList.BeginRefresh();
if (String.IsNullOrWhiteSpace(e.NewTextValue))
{
StudentList.ItemsSource = PersonsList;
}
else
{
StudentList.ItemsSource = PersonsList.Where <Person>(i => i.Name.ToLower().StartsWith(e.NewTextValue.ToLower()) ||
i.Surname.ToLower().StartsWith(e.NewTextValue.ToLower()) || i.Pseudo != null && (i.Pseudo.ToLower().StartsWith(e.NewTextValue.ToLower())));
}
StudentList.EndRefresh();
}