Alert message from C#

Question

Is there any other way to display alert message from back end in asp.net web application rather than this.

ScriptManager.RegisterStartupScript(this, GetType(), "alertMessage","alert('Called from code-behind directly!');", true);

I have included using System.Web.UI namespace also, but still am getting these 2 errors with this code:

First error:

The best overloaded method match for 'System.Web.UI.ScriptManager.RegisterStartupScript(System.Web.UI.Page, System.Type, string, string, bool)' has some invalid arguments D:\my_backup\Demos\NewShop\NewShop\API\ProductAPIController.cs 85 17 N‌​ewShop

Second error:

Argument 1: cannot convert from 'NewShop.API.ProductAPIController' to 'System.Web.UI.Page' D:\my_backup\Demos\NewShop\NewShop\API\ProductAPIController‌​.cs 85 53 NewShop

Answer 1

The error messages tell you what is wrong. The RegisterStartupScript method requires a first argument of type System.Web.UI.Page, which is used in ASP.NET WebForms. Instead you are passing this as the first argument, which is a Controller class, which is used in ASP.NET MVC!

That means the code you are using is meant for another web architecture. To control JavaScript output from a Controller, you are much better off using the Model or maybe ViewBag. Like this:

In your controller code

ViewBag.ShowAlert = true;

In your view

@if (ViewBag.ShowAlert)
{
    <script>alert("(Almost) called from code-behind");</script>
}

If you need full control over the script that is rendered, save the script as a string in the ViewBag, even though this is definitely not recommended!

In your controller code

ViewBag.SomeScript = "alert('Added by the controller');";

In your view

@if (ViewBag.SomeScript != null)
{
    <script>@Html.Raw(ViewBag.SomeScript)</script>
}