如何取消CTreeCltr中Item的选择

用SetItemState并不能够清除选择，看下面代码，不能够弹出对话框来。请问高手们，这是怎么回事，怎样才能够弹出那个对话框阿！谢谢！HTREEITEM hTreeItemCurrent = m_treeCtrl.GetSelectedItem();
if (hTreeItemCurrent != NULL)
{
m_treeCtrl.SetItemState(hTreeItemCurrent, 0, TVIS_SELECTED);
HTREEITEM hItem = m_treeCtrl.GetSelectedItem();
if (hItem == NULL)
{
AfxMessageBox(_T("选择为空"));
}
}