Usage

Namespace

To use GongSolutions.WPF.DragDrop in your application you need to add the namespace to your Xaml files.

xmlns:dd="urn:gong-wpf-dragdrop"

or

xmlns:dd="clr-namespace:GongSolutions.Wpf.DragDrop;assembly=GongSolutions.Wpf.DragDrop"

Default Behaviour

A simple example of adding drag/drop to a ListBox:

<ListBox ItemsSource="{Binding Collection}"
         dd:DragDrop.IsDragSource="True"
         dd:DragDrop.IsDropTarget="True" />

Setting the IsDragSource and IsDropTarget attached propeties to True on an ItemsControl such as ListBox enables drag and drop. The default behaviour is to allow re-ordering of items within the control.

If your project contains another ItemsControl with drag/drop enabled in this manner, and it is bound to a collection of the same type, then items can also be dragged and dropped between the controls.

Adding a Drop Handler

While the defaults can be useful in simple cases, you will usually want more control of what happens when data is dragged/dropped onto your control. You can delegate that responsibility to your ViewModel by setting the DropHandler attached property:

<ListBox ItemsSource="{Binding Collection}"
         dd:DragDrop.IsDragSource="True"
         dd:DragDrop.IsDropTarget="True"
         dd:DragDrop.DropHandler="{Binding}" />

In this example, we're binding the drop handler to the current DataContext, which will usually be your ViewModel.

You handle the drop in your ViewModel by implementing the IDropTarget interface:

class ExampleViewModel : IDropTarget
{
	public ObservableCollection<ExampleItemViewModel> Items;
	
	void IDropTarget.DragOver(IDropInfo dropInfo) {
		ExampleItemViewModel sourceItem = dropInfo.Data as ExampleItemViewModel;
		ExampleItemViewModel targetItem = dropInfo.TargetItem as ExampleItemViewModel;
		
		if (sourceItem != null && targetItem != null && targetItem.CanAcceptChildren) {
			dropInfo.DropTargetAdorner = DropTargetAdorners.Highlight;
			dropInfo.Effects = DragDropEffects.Copy;
		}
	}
	
	void IDropTarget.Drop(IDropInfo dropInfo) {
		ExampleItemViewModel sourceItem = dropInfo.Data as ExampleItemViewModel;
		ExampleItemViewModel targetItem = dropInfo.TargetItem as ExampleItemViewModel;
		targetItem.Children.Add(sourceItem);
	}
}

class ExampleItemViewModel
{
	public bool CanAcceptChildren { get; set; }
	public ObservableCollection<ExampleItemViewModel> Children { get; private set; }
}

In this example, we're checking that the item being dragged and the item being dropped onto are both ExampleItemViewModels and that the target item allows items to be added to its Children collection. If the drag satisfies both of these conditions, then the function tells the framework to display a Copy mouse pointer, and to use a Highlight drop target adorner.

For more information, check out the full DropHandlerExample.

Next : In action