Microsoft ASP.NET 4 : Diagnostics and Debugging - Error Pages

Open the DebugORama project.

Add a new Web Form named ThrowErrors.aspx to the DebugORama application.

Add two buttons: one to throw 404 errors (the nearly ubiquitous "object not found" error) and one to throw other exceptions. Set the 404 button's ID to ButtonThrow404 and set the other button's ID to ButtonThrowOther.

Add two HTML pages to your application to act as custom error pages. Name one page 404Error.htm and the other SomethingBadHappened.htm. (This example uses straight HTML pages, although you can use ASPX files here.) The following graphic shows the 404Error.htm file being added to the Web solution.

Here is the SomethingBadHappened.htm page being added:

Add some content to the error pages. The 404 error handler here displays an error message in haiku. The other error page simply displays a label saying "Something bad happened."

Tell ASP.NET to use the error pages by adding the customErrors section to web.config, like so:

<configuration>
   <system.web>
      <customErrors
         defaultRedirect="SomethingBadHappened.htm" mode="On">
            <error statusCode="404"
               redirect="404Error.htm"/>
      </customErrors>
   </system.web>
</configuration>

This tells ASP.NET to show the 404Error.htm page when a file isn't found. ASP.NET will show SomethingBadHappened.htm for any other type of error.

Now add handlers to generate the errors. Handle the 404 error button by directing the client to a nonexistent page: In this example, there is no page named NonExistent.aspx, so redirecting to it will cause a 404 error. Handle the second error generator by throwing a random exception.

public partial class ThrowErrors : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }

    protected void ButtonThrow404_Click(object sender, EventArgs e)
    {
        this.Response.Redirect("NonExistent.aspx");
    }

    protected void ButtonThrowOther_Click(object sender, EventArgs e)

    {
        throw new Exception();
    }
}

When you try to redirect to a nonexistent file, the "object not found" error page shows:

Throwing a generic exception causes the other page to show: