void WhenDragOver(DragEventArgs e) { if (_manager == null) { return; } var point = treeView1.PointToClient(new Point(e.X, e.Y)); var node = treeView1.GetNodeAt(point); if (null == node) { return; } if (node.Tag is ProjectId) { var requestId = (string)e.Data.GetData(DataFormats.StringFormat); var projectId = (ProjectId)node.Tag; if (_manager.CanDropToProject(requestId, projectId)) { e.Effect = DragDropEffects.Move; } else { e.Effect = DragDropEffects.None; } } else { e.Effect = DragDropEffects.None; } // }