Server-side Selection

There might be scenarios where you need to perform server-side selection for the RadTreeList items.For that purpose, you can use one of the below approaches:

• Add a TreeListSelectColumn and provide the ability to the user to select the desired items through it.

• Use server-side code to programmatically select the treelist items.

In both cases, to enable multi-item selection, you need to set the RadTreeList AllowMultiItemSelection property to true.

Using the TreeListSelectColumn

RadTreeList server-side selection is enabled for the users once you add the TreeListSelectColumn to the RadTreeList Columns collection. You do not need to set any additional properties. Then checking the checkbox rendered in the column marks the corresponding item as selected. As a result, postback is performed and the ItemCommand event is fired with command name RadTreeList.SelectCommandName. To deselect an item,one should uncheck the checkbox in the select column. Then again postback is performed and theItemCommand event is fired with command name RadTreeList.DeselectCommandName.

<telerik:RadTreeList RenderMode="Lightweight" ID="RadTreeList1" runat="server" DataKeyNames="EmployeeID" DataSourceID="SqlDataSource1"
    ParentDataKeyNames="ReportsTo" AllowMultiItemSelection="True" OnItemCommand="RadTreeList1_ItemCommand">
    <Columns>
        <telerik:TreeListSelectColumn UniqueName="SelectColumn">
        </telerik:TreeListSelectColumn>
    </Columns>
</telerik:RadTreeList>
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>"
    SelectCommand="SELECT [EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [City], [ReportsTo] FROM [Employees]">
</asp:SqlDataSource>

protected void RadTreeList1_ItemCommand(object sender, Telerik.Web.UI.TreeListCommandEventArgs e)
{
    if (e.CommandName == RadTreeList.SelectCommandName)
    {
        //item is being selected    
    }
    if (e.CommandName == RadTreeList.DeselectCommandName)
    {
        //item is being deselected    
    }
}           

Protected Sub RadTreeList1_ItemCommand(ByVal sender As Object, ByVal e As Telerik.Web.UI.TreeListCommandEventArgs)
    If e.CommandName = RadTreeList.SelectCommandName Then
        'item is being selected    
    End If
    If e.CommandName = RadTreeList.DeselectCommandName Then
        'item is being deselected    
    End If
End Sub

Programmatic items selection

To select an item/items with server-side code, you can set the particular item/items Selected property to true:

protected void Page_PreRender(object sender, EventArgs e)
{
    TreeListDataItem item = RadTreeList1.Items[0];
    item.Selected = true;
}           

Protected Sub Page_PreRender(ByVal sender As Object, ByVal e As EventArgs) Handles Me.PreRender
    Dim item As TreeListDataItem = RadTreeList1.Items(0)
    item.Selected = True
End Sub

Deselecting items programmatically

To deselect an item/items programmatically, set its Selected property to false.

You can also call the ClearSelectedItems() method of the RadTreeList control to deselect all selected items which are visible on the current page.