/// <summary>
/// Occurs when activity of the current drag drop operation has changed.
/// </summary>
/// <param name="sender">The event source.</param>
/// <param name="e">The event data.</param>
protected virtual void OnDragActivityChanged(object?sender, EventArgs e)
{
Contract.RequireNotNull(sender, out IDragSourceControl Ctrl);
bool IsHandled = false;
switch (Ctrl.DragActivity)
{
case DragActivity.Idle:
IsHandled = true;
break;
case DragActivity.Starting:
bool IsDragPossible = DragSource.IsDragPossible(out _, out IList ItemList);
Debug.Assert(IsDragPossible);
SetDragItemList(DragSource, ItemList);
CancellationToken cancellation = new CancellationToken();
NotifyDragStarting(cancellation);
if (cancellation.IsCanceled)
{
Ctrl.CancelDrag();
}
IsHandled = true;
break;
case DragActivity.Started:
DataObject Data = new DataObject(DragSource.GetType(), DragSource);
DragDropEffects AllowedEffects = DragDropEffects.Move;
if (DragSource.AllowDropCopy)
{
AllowedEffects |= DragDropEffects.Copy;
}
DragDrop.DoDragDrop(this, Data, AllowedEffects);
ClearCurrentDropTarget();
IsHandled = true;
break;
default:
break;
}
Debug.Assert(IsHandled);
}
/// <summary>
/// Gets the drag source from arguments of a drag drop event.
/// </summary>
/// <param name="e">The event data.</param>
/// <param name="dragSource">The drag source upon return.</param>
/// <returns>True if successful.</returns>
protected virtual bool GetValidDragSourceFromArgs(DragEventArgs e, out IDragSourceControl dragSource)
{
if (e.Data.GetDataPresent(DragSource.GetType()))
{
if (e.Data.GetData(DragSource.GetType()) is IDragSourceControl AsDragSource)
{
if (AsDragSource.HasDragItemList(out object RootItem, out IList _) && IsSameTypeAsContent(RootItem))
{
dragSource = AsDragSource;
return(true);
}
}
}
Contract.Unused(out dragSource);
return(false);
}
/// <summary>
/// Invoked when an unhandled <see cref="UIElement.Drop"/> attached event reaches an element in its route that is derived from this class.
/// </summary>
/// <param name="e">The event data.</param>
protected override void OnDrop(DragEventArgs e)
{
e.Effects = GetAllowedDropEffects(e);
e.Handled = true;
if (e.Effects != DragDropEffects.None)
{
ExtendedTreeViewItemBase?ItemContainer = GetEventSourceItem(e);
IDragSourceControl AsDragSource = (IDragSourceControl)e.Data.GetData(DragSource.GetType());
bool IsDragPossible = AsDragSource.IsDragPossible(out object SourceItem, out IList ItemList);
object?DestinationItem = ItemContainer != null ? ItemContainer.Content : null;
UnselectAll();
if (IsDragPossible && DestinationItem != null)
{
IList CloneList = CreateItemList();
Debug.Assert(CloneList.Count == 0);
NotifyPreviewDropCompleted(DestinationItem, e.Effects, ItemList, CloneList);
if (e.Effects == DragDropEffects.Copy)
{
DragDropCopy(SourceItem, DestinationItem, ItemList, CloneList);
}
else if (e.Effects == DragDropEffects.Move)
{
DragDropMove(SourceItem, DestinationItem, ItemList);
}
Debug.Assert(CloneList.Count > 0 || e.Effects != DragDropEffects.Copy);
NotifyDropCompleted(DestinationItem, e.Effects, ItemList, CloneList);
Expand(DestinationItem);
}
}
}
