ComboBox with empty item?

Question

Suppose we have a DataSource bind to a collection from Database. There is no null item of course. How to add a void item into a ComboBox, so that at first l

Answer 1

    



    
        
            
            
        
    


public class ComboBox : System.Windows.Controls.ComboBox
{
    public static readonly DependencyProperty IsNullableProperty =
        DependencyProperty.Register("IsNullable", typeof(bool), typeof(ComboBox));

    public bool IsNullable
    {
        get { return (bool)GetValue(IsNullableProperty); }
        set { SetValue(IsNullableProperty, value); }
    }

    public ComboBox()
    {
        Loaded += ComboBox_Loaded;
    }

    void ComboBox_Loaded(object sender, RoutedEventArgs e)
    {

        if (IsNullable)
        {
            this.ItemContainerStyle = new Style();

            this.ItemContainerStyle.Setters.Add(new EventSetter()
            {
                Event = ComboBoxItem.PreviewMouseUpEvent,
                Handler = new MouseButtonEventHandler(cmbItem_PreviewMouseUp)
            });
        }
    }

    public void cmbItem_PreviewMouseUp(object sender, MouseButtonEventArgs e)
    {
        if (Items.IndexOf(sender as ComboBoxItem) == 0)
        {
            SelectedItem = null;
        }
    }
}