asp.net - Programmatically change a TreeView expand depth

Change TreeView expand depth programmatically
The TreeView is an asp.net web server control. The TreeView is located under System.Web.UI.WebControls namespace. TreeView web server control displays hierarchical data. Such as a table of contents in a tree structure.

The following asp.net c# tutorial code demonstrates how we can change the TreeView expand depth programmatically. The asp.net c# developers can change the expand depth of a TreeView programmatically using its ExpandDepth property.

The TreeView ExpandDepth property gets or sets the number of levels that are expanded when a TreeView control is displayed for the first time. This property value is an Int32 which is the depth to display when the TreeView is initially displayed. The default is -1, which displays all the nodes.

The asp.net c# developers need to use the TreeView ExpandDepth property to control the rendering of the TreeView control the first time that it is displayed. On subsequent postbacks, the nodes retain their current expanded state. In this tutorial code we set the TreeView expand depth on page load event.
TreeViewExpandDepth.aspx

<%@ Page Language="C#" %>

<!DOCTYPE html>

<script runat="server">
    protected void Page_Load(object sender, System.EventArgs e)
    { 
        if(!this.IsPostBack)
        {
            TreeView1.ExpandDepth = 1;
        }
    }
    protected void Button1_Click(object sender, System.EventArgs e)
    {
        TreeView1.ExpandAll();
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>How to set, change TreeView expand depth (ExpandDepth) in page load</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:Navy">TreeView Example: ExpandDepth</h2>
        <asp:SiteMapDataSource ID="SiteMapDataSource1" runat="server" />
        <asp:TreeView 
             ID="TreeView1"
             runat="server"
             DataSourceID="SiteMapDataSource1"
             Width="250"
             BackColor="SkyBlue"
             ForeColor="White"
             >
        </asp:TreeView>
        <br />
        <asp:Button 
             ID="Button1" 
             runat="server"
             ForeColor="SteelBlue"
             Text="TreeView Expand All"
             Height="45"
             OnClick="Button1_Click"
             Font-Bold="true"
             />
    </div>
    </form>
</body>
</html>
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