private void treeView_AcceptingDraggedNode(object source, AcceptingDraggedNodeEventArgs e)
{
/*
* This example enforces the following:
* - Folders should only exist at the top level
* - Leaves can exist at the top level or inside a folder
*
* Determining whether a node is a leaf or a folder is based on ImageIndex.
* 0 = folder, 1 = leaf. In a real application, this mechanism would probably
* be replaced with something a litle better (using the Tag property of each
* node, for example).
*/
// Don't allow a folder to become buried
if (e.NodeMoving.ImageIndex == 0 && e.NodeOver.Level > 0)
{
e.PreventAnyDrop = true;
}
// Don't allow folders to be dropped as childen under anything
if (e.NodeMoving.ImageIndex == 0)
{
e.PreventDropAsChild = true;
}
// Don't allow dropping under non-zero items (non-folders)
if (e.NodeOver.ImageIndex > 0)
{
e.PreventDropAsChild = true;
}
}
private void DragDropTreeView_DragOver(object sender, DragEventArgs e)
{
var clientPos = PointToClient(Cursor.Position);
// Scroll the tree up/down if necessary
if (AutoScrollEnabled)
{
AutoScroll(clientPos);
}
var nodeOver = GetNodeAt(clientPos);
var nodeMoving = (TreeNode)e.Data.GetData("System.Windows.Forms.TreeNode");
// nodeOver must not be null, and nodeOver must not be the same as nodeMoving UNLESS
// nodeOver is the last node in the branch (so it is possible to drop below a parent branch)
if (nodeOver != null && (nodeOver != nodeMoving || (nodeOver.Parent != null && nodeOver.Index == (nodeOver.Parent.Nodes.Count - 1))))
{
var offsetY = PointToClient(Cursor.Position).Y - nodeOver.Bounds.Top;
// Prevent paradoxes here and now
if (CausesParadox(nodeOver, nodeMoving))
{
SetPlaceholders(PlaceholderLocation.None, null, null);
return;
}
// Create a new event args object for the AcceptingDraggedNode event.
var args = new AcceptingDraggedNodeEventArgs(nodeOver, nodeMoving);
// Fire the event (if there is a handler attached)
if (AcceptingDraggedNode != null)
{
AcceptingDraggedNode(this, args);
}
if (args.PreventAnyDrop)
{
SetPlaceholders(PlaceholderLocation.None, null, null);
e.Effect = DragDropEffects.None;
return;
}
e.Effect = DragDropEffects.Move;
if (args.PreventDropAsChild)
{
// Node does not accept children (is a leaf)
// Collapse so we don't get weirdness when dropping below the node
// but apparently above its children nodes.
if (nodeOver.IsExpanded)
{
nodeOver.Collapse(true);
}
HandleDraggingOverNonChildAcceptingNode(offsetY, nodeOver);
}
else
{
// Node accepts children
HandleDraggingOverChildAcceptingNode(offsetY, nodeOver, nodeMoving);
}
}
}
