Adding and Editing Templates at Runtime

You can also add Templates to RadTreeView at runtime, using the NodeTemplate property. This property is of type ITemplate, so you must assign an object that implements that interface as a value:

The TreeNodes should be dynamically added so that Templates can be defined at run time. Also, the Nodes should be bound to be able to eval DataBinder expressions. In other words, you should call the DataBind method of the RadTreeView object or bind the Nodes that are about to use DataBinder.Eval. You can bind a specific node by calling the DataBind method of this specific Node.

The NodeTemplate should be initialized in the OnInit event of the page. This is needed as the Template should be instantiated before the TreeNodes are initialized.

C#

protected override void OnInit(EventArgs e)
{
    RadTreeView1.NodeTemplate = new TextBoxTemplate();
    base.OnInit(e);
}

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        RadTreeView1.Nodes.Add(new RadTreeNode("root1")); RadTreeView1.Nodes.Add(new RadTreeNode("root2"));
    }

    RadTreeView1.DataBind();
}

class TextBoxTemplate : ITemplate
{
    public void InstantiateIn(Control container)
    {
        Label label1 = new Label();
        label1.ID = "ItemLabel";
        label1.Text = "Text";
        label1.Font.Size = 10;
        label1.Font.Bold = true;
        label1.DataBinding += new EventHandler(label1_DataBinding);
        container.Controls.Add(label1);
    }

    private void label1_DataBinding(object sender, EventArgs e)
    {
        Label target = (Label)sender;
        RadTreeNode node = (RadTreeNode)target.BindingContainer;
        string nodeText = (string)DataBinder.Eval(node, "Text");
        target.Text = nodeText;
    }
}

VB.NET

Protected Overloads Overrides Sub OnInit(ByVal e As EventArgs)
    RadTreeView1.NodeTemplate = New TextBoxTemplate()
    MyBase.OnInit(e)
End Sub

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    If Not Page.IsPostBack Then
        RadTreeView1.Nodes.Add(New RadTreeNode("root1"))
        RadTreeView1.Nodes.Add(New RadTreeNode("root2"))
    End If
    RadTreeView1.DataBind()
End Sub

Class TextBoxTemplate
    Implements ITemplate
        Public Sub InstantiateIn(ByVal container As Control) Implements InstantiateIn
        Dim label1 As New Label()
        label1.ID = "ItemLabel"
        label1.Text = "Text"
        label1.Font.Size = 10
        label1.Font.Bold = True
        AddHandler label1.DataBinding, AddressOf label1_DataBinding
        container.Controls.Add(label1)
    End Sub
    Private Sub label1_DataBinding(ByVal sender As Object, ByVal e As EventArgs)
        Dim target As Label = DirectCast(sender, Label)
        Dim node As RadTreeNode = DirectCast(target.BindingContainer, RadTreeNode)
        Dim nodeText As String = DirectCast(DataBinder.Eval(node, "Text"), String)
        target.Text = nodeText
    End Sub
End Class

If you want to add different templates to specific nodes, based on some property or value for instance, the best way is to use the TemplateNeeded event.

C#

protected void RadTreeView1_TemplateNeeded(object sender, Telerik.Web.UI.RadTreeNodeEventArgs e)
{
    string value = e.Node.Value;
    if (value != null)
    {
        // if the value is an even number
        if ((Int32.Parse(value) % 2) == 0)
        {
            var textBoxTemplate = new TextBoxTemplate();
            e.Node.NodeTemplate = textBoxTemplate;
        }
    }
}	

VB.NET

Sub RadTreeView1_Template(ByVal sender As Object, ByVal e As Telerik.Web.UI.RadTreeNodeEventArgs) Handles RadTreeView1.TemplateNeeded
    Dim value As String = e.Node.Value
    If value IsNot Nothing Then
        ' if the value is an even number
        If ((Int32.Parse(value) Mod 2) = 0) Then
            Dim textBoxTemplate As TextBoxTemplate = New TextBoxTemplate()
            e.Node.NodeTemplate = textBoxTemplate
        End If
    End If
End Sub

If for some reason you cannot define the Template in the OnInit event of the page, or take advantage of the TemplateNeeded event, you could use another approach:

The Template has to be instantiated for each Node upon a postback. Since the TextBoxTemplate class initializes the Label on InstantiateIn we called the InstantiateIn method of the TextBoxTemplate object for each Node.

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        RadTreeView1.Nodes.Add(new RadTreeNode("root1"));
        RadTreeView1.Nodes.Add(new RadTreeNode("root2"));
    }

    TextBoxTemplate template = new TextBoxTemplate();

    foreach (RadTreeNode node in RadTreeView1.GetAllNodes())
    {
        template.InstantiateIn(node);
    }

    RadTreeView1.DataBind();
}

VB.NET

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    If Not Page.IsPostBack Then
        RadTreeView1.Nodes.Add(New RadTreeNode("root1"))
        RadTreeView1.Nodes.Add(New RadTreeNode("root2"))
    End If
    Dim template As New TextBoxTemplate()
    For Each node As RadTreeNode In RadTreeView1.GetAllNodes()
        template.InstantiateIn(node)
    Next
    RadTreeView1.DataBind()
End Sub

The end result of this code looks like the following: