WPF drag and drop from a ListBox that has SelectionMode=Extended

Question

I have a ListBox and want the selection-mode to be extended. Also I want have to implement drag and drop functionality. The problem now is, that if the mouse is clicked on a

Answer 1

Here's what I've done. In your DragDrop code, subscribe to the PreviewMouseLeftButtonDown. If the item you are already clicking on is selected, then set e.Handled to true.

In my sample below, I identify a part of the list box item as a drag grip (with bumps) so that I can distinguish between the item and a drag surface. I just had to get the list box item data template and the drag and drop behavior to agree on a name of the drag grip element.

The PreviewMouseLeftButtonDown from my work in progress:

private void ItemsControl_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    dragStartPoint = e.GetPosition(null);

    ItemsControl itemsControl = this.AssociatedObject as ItemsControl;
    if (itemsControl != null)
    {
        this.sourceItemContainer = itemsControl.ContainerFromElement((Visual)e.OriginalSource) as FrameworkElement;
    }

    // If this is an multiple or extended selection list box, and on a drag grip, then ensure the item being hit is selected
    // This prevents the ItemsControl from using this MouseDown to change selection, except over a selected item's drag grip.            
    if ((this.IsMultipleSelectionListBox() == true) && (this.IsOriginalSourceDragGrip(e) != false) && (this.IsSourceListBoxItemSelected() == true))
    {
        e.Handled = true;
    }
}

Answer 2

Use PreviewMouseLeftButtonDown to add the selected items for the drag operation.

Answer 3

The easiest workaround i can think of would be to change the ListBoxItem to select on MouseUp not Down like so and change the ContainerGenerator to serve your custom ListBoxItems:

public class CustomListBoxItem : ListBoxItem  
{  
    protected override void OnMouseLeftButtonDown( MouseButtonEventArgs e )  
    {  
        //do nothing
    }  

    protected override void OnMouseLeftButtonUp( MouseButtonEventArgs e )  
    {  
        base.OnMouseLeftButtonDown( e );  
    }  
}  

You might need some MouseLeave/LeftButtonDown logic if you want to prevent different items selecting when moving through the List while holding the mouse button down.