解决treeview未选中时，默认选中首个根节点的问题！

private void treeView1_MouseUp(object sender, MouseEventArgs e)
{ TreeNode selectnode = this.treeView1.GetNodeAt(e.Location);
if (selectnode == null)
{
this.treeView1.SelectedNode = null; } } private void treeView1_BeforeSelect(object sender, TreeViewCancelEventArgs e)
{
if (e.Action == TreeViewAction.Unknown)
e.Cancel = true;
}