How to display an error message box in a web application asp.net c#

Question

I have an ASP.NET web application, and I wanted to know how I could display an error message box when an exception is thrown.

For example,

Answer 1

If you are using .NET Core with MVC and Razor, you have several levels of preprocessing before your page is rendered. Then I suggest that you try wrapping a conditional error message at the top of your view page, like so:

In ViewController.cs:

if (file.Length < 800000)
{
    ViewData["errors"] = "";
}
else
{
    ViewData["errors"] = "File too big. (" + file.Length.ToString() + " bytes)";
}

In View.cshtml:

@if (ViewData["errors"].Equals(""))
{
    @:
Everything is fine.
}
else
{
    @:
}