button如何取的treeview的节点
button如何取的treeview的节点：

页面左边有个treeview用来显示单位
右边有button用来查询的，有一系列的下拉框用来拼接sql条件的

<asp:TreeView ID="TreeView1" runat="server" OnSelectedNodeChanged="TreeView1_SelectedNodeChanged"
                            OnLoad="TreeView1_Load">
                      
                            <SelectedNodeStyle ForeColor="Red" Font-Bold="True" />
                        </asp:TreeView>


我的代码为
protected void btnSearch_Click(object sender, EventArgs e)
        {
            ViewState["DropDownList1"] = DropDownList1.SelectedValue;
            ViewState["DropDownList2"] = DropDownList2.SelectedValue;
            string startdate = DropDownList1.SelectedValue + DropDownList2.SelectedValue;
 if (zzjg == "dydm")
            {
                if (TreeView1.SelectedNode.Depth == 2 && TreeView1.SelectedNode.ChildNodes.Count == 0)
                {
                    Dictionary<string, string> yqt = sql_Organization1(a);
                    foreach (var y in yqt)
                    {
                        if (yqt.Count > 0)
                        {
                            TreeView1.SelectedNode.ChildNodes.Add(new TreeNode(y.Value, y.Key));
                        }
                    }

                }
            }

 if (TreeView1.SelectedNode.ChildNodes.Count == 0)???????????
  我这个条件就取不到树形节点，老是为空错在这里的
｛
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