Hello.

This question is related to Treepanel use.

A Treepanel clicking on the Tree of B Treepanel should try to change dynamically.

What should I do?

Written source code is shown below.

Runtime runtime error occurs
"Microsoft JScript runtime error: 'this.root' that (a) null or not an object."

aspx code
...

<ext:Panel ID="Panel6" runat="server" Title="" Width="175">
                            <Items>
                                <ext:RowLayout ID="RowLayout1" runat="server" Split="true">
                                    <Rows>
                                        <ext:LayoutRow RowHeight="0.45">
                                            <ext:Panel runat="server" Title="System Tree">
                                                <Items>
                                                    <ext:TreePanel ID="left_top" runat="server" AutoHeight="false" Border="false">
                                                        <Loader>
                                                            <ext:WebServiceTreeLoader DataUrl="TreeLoaderService.asmx/Get_TopNodes" />
                                                        </Loader>
                                                        <Listeners>
                                                            <Click Handler="Tree_view(left_top, node);" />
                                                        </Listeners>
                                                    </ext:TreePanel>
                                                </Items>
                                            </ext:Panel>
                                        </ext:LayoutRow>
                                        
                                        <ext:LayoutRow RowHeight="0.25">
                                            <ext:Panel ID="mid_panel" runat="server" Title="Content Tree" >
                                                <Items>
                                                    <ext:TreePanel ID="left_mid" runat="server" AutoHeight="false" Visible="false">
                                                        <Root>
                                                            <ext:TreeNode NodeID="1" Text="Txt"></ext:TreeNode>
                                                        </Root>
                                                    </ext:TreePanel>
                                                </Items>
                                            </ext:Panel>
                                        </ext:LayoutRow>
                                        
                                        <ext:LayoutRow RowHeight="0.30">
                                            <ext:Panel ID="left_foot" runat="server" Title="Content Attribute" />
                                        </ext:LayoutRow>
                                    </Rows>
                                </ext:RowLayout>
                            </Items>
                        </ext:Panel>
...
cs code
...

protected void btn_midCreate_Click(object sender, EventArgs e)
    {
        string par_1 = hidden_id.Value.Split('|')[0];


        string par_lvl = par_1.Split('^')[0]; // level
        string par_id = par_1.Split('^')[1]; // id
        string par_text = hidden_id.Value.Split('|')[1]; // text


        left_mid.Root.Clear();


        Ext.Net.TreeNode root = CreateNode(par_id, par_text);


        left_mid.Root.Add(root);


        left_mid.Visible = true;
    }


    private Ext.Net.TreeNode CreateNode(string id, string txt)
    {
        Ext.Net.TreeNode t = new Ext.Net.TreeNode();


        t.NodeID = id;
        t.Text = txt;


        oMain_Tree.open();


        DataSet oTreeSubDs = oMain_Tree.M_Get_Tree("99", id);


        if (oTreeSubDs.Tables.Count > 0)
        {
            foreach (DataRow row in oTreeSubDs.Tables[0].Rows)
            {
                t.Nodes.Add(this.CreateNode(row["Tree_id"].ToString(), row["name"].ToString()));
            }
        }


        oMain_Tree.close();
        return t;
    }
...