Extension methods in a class library project

Question

I've implemented some extension methods and put those in separate Class Library project.

Imagine I have a simple extension method like this in class library called MD.Utility:

namespace MD.Utility
{
    public static class ExtenMethods
    {
        public static bool IsValidEmailAddress(this string s)
        {
            Regex regex = new Regex(@"^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$");
            return regex.IsMatch(s);
        }
    } 
}

But nowhere in the web app like the App_code folder or the WebFroms code-behind page can I use this extension method. If I do something like this:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using MD.Utility;

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string email = "[email protected]";
        if (email.IsValidEmailAddress())
        {
            //To do 
        }
    }
}

The compiler doesn't recognize IsValidEmailAddress() and there's even no IntelliSense support.

While if I put my extension method in the App_Code folder, it's usable in another .cs files in the App_code folder or the WebForms code-behind pages.

Answer 1

Did you remember to add a reference to your class library in the web project ?

You will need that. Other than that, your code looks fine, and should work.

Answer 2

If changes are not getting recompiled when you do a solution rebuild, then it could be the type of reference you are using. If the MD.Utility project is in your web project solution, you should make the reference a "Project Reference." That will cause the build to consider that code as a dependency and therefore rebuild it when you change something. If you just include it as a DLL, then the DLL is considered external and the build will not consider it, even if it is in the same solution.