In this article I will explain with an example, how to open (show) AJAX ModalPopupExtender Modal Popup from Code-Behind (Server-Side) in ASP.Net using C# and VB.Net.
 
 

Installing and Registering AjaxControlToolkit package using Nuget

In order to install and register AJAX Control Toolkit library using Nuget, please refer my article Install AjaxControlToolkit library using Nuget.
 
 

HTML Markup

The HTML Markup consists of following controls:
ScriptManager – For enabling ASP.Net AJAX.
LinkButton – For triggering the Modal popup to open.
ModalPopupExtender – For displaying Modal popup.
The AJAX ModalPopupExtender has been assigned with following properties:
TargetControlID – The control where the Text will displayed.
PopupButtonID – The control which opens the Calendar.
CancelControlID – The control which closes the Calendar.
Note: For more details on using the AJAX ModalPopupExtender, please refer my article Building Modal Popup using ASP.Net AJAX ModalPopupExtender Control.
 
Panel – For displaying content of the Modal popup.
Button – For hiding the Modal popup dialog box.
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<asp:LinkButton ID="lnkDummy" runat="server"></asp:LinkButton> 
<ajaxToolkit:ModalPopupExtender ID="ModalPopupExtender1" runat="server" PopupControlID="pnlPopup" TargetControlID="lnkDummy" BackgroundCssClass="modalBackground" CancelControlID="btnHide">
</ajaxToolkit:ModalPopupExtender>
<asp:Panel ID="pnlPopup" runat="server" CssClass="modalPopup" Style="display:none"> 
    <div class="header">Modal Popup</div>
    <div class="body">This is a ModalPopup.<br />
        <asp:Button ID="btnHide" runat="server" Text="Hide Modal Popup" /> 
    </div>
</asp:Panel>
 
 

Opening AJAX ModalPopupExtender Modal Popup from Code-Behind (Server-Side) in ASP.Net

Inside the Page_Load event handler, the AJAX ModalPopupExtender Modal Popup is opened (shown) using Show method.
C#
protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        ModalPopupExtender1.Show();
    }
}
 
VB.Net
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        ModalPopupExtender1.Show()
    End If
End Sub
 
 

Modal Popup CSS

The following CSS is used for styling the ASP.Net AJAX ModalPopupExtender.
<style type="text/css">
    body { font-family: Arial; font-size: 10pt; }
    .modalBackground { background-color: Black; filter: alpha(opacity=60); opacity: 0.6; }
    .modalPopup { background-color: #FFFFFF; width: 300px; border: 3px solid #0DA9D0; padding: 0; }
    .modalPopup .header { background-color: #2FBDF1; height: 30px; color: White; line-height: 30px; text-align: center; font-weight: bold; }
    .modalPopup .body { min-height: 50px; line-height: 30px; text-align: center; font-weight: bold; margin-bottom: 5px; }
</style>
 
 

Screenshot

Open (Show) ASP.Net AJAX Modal Popup from Code Behind (Server Side) in ASP.Net
 
 

Demo

View Demo
 
 

Downloads

Download Code