private void TreeView_DragOver(object sender, DragEventArgs e) { if (Handler == null) { return; } e.Effect = DragDropEffects.None; if (draggedNodes != null && UI.TreeView.DropPosition.Node != null) { TreeNodeAdv dropTarget = UI.TreeView.DropPosition.Node; if (TreeModel.CanDrop(draggedNodes, dropTarget, UI.TreeView.DropPosition.Position)) { e.Effect = DragDropEffects.Move; } } }