Use UIElements MaskField to select data

[Mask(nameof(DataSource))]
public int IntValue;
 
private static DropdownList DataSource()
{
    var list = new DropdownList();
    list.Add(1, "One");
    list.Add(2, "Two");
    list.Add(4, "Three");
    return list;
}

A data source is required, as described in DropdownAttribute