1 private void treeView1_MouseUp(object sender, MouseEventArgs e) 2         { 3               4             TreeNode selectnode = this.treeView1.GetNodeAt(e.Location); 5             if (selectnode == null) 6             { 7                 this.treeView1.SelectedNode = null; 8   9             }  10  11         }12  13         private void treeView1_BeforeSelect(object sender, TreeViewCancelEventArgs e)14         {15             if (e.Action == TreeViewAction.Unknown)16                 e.Cancel = true;17         }