C# with Mono

I’ve been wanting to learn C#. It seems everything is done in C# these days. But I have a Mac. I thought that the only way to program with C# would be on Windows XP via WMWare, but after a bit of research I found I was mistaken.

Enter Mono. (Mono, as in the prefix meaning “one,” not as in the disease.) Mono is an open source, cross platform implementation of the .Net Framework. It is available on a large number of platforms, including Mac OS X, Windows and Linux. Sounds cool, eh? That’s what I thought anyway. So I was excited to download and try it. It even comes with it’s own little IDE, MonoDevelop.

After I installed Mono and MonoDevelop, I was able to compile a quick “Hello World” console application. That was fun and easy. I wondered if I would be able to do the same with a Windows.Forms application. This is where I ran into some complications.

Whenever I tried to use System.Windows.Forms, I would get the following error:

The type or namespace name ‘Windows’ does not exist in the namespace ‘System’. Are you missing an assembly reference?

I searched all around to see what this could possibly mean. The Mono Project website said they supported Windows.Forms on Mac OS X. I had the full version of Mono. I reinstalled Mono and MonoDevelop several times. Unfortunately, since Mono is so new and there isn’t much of a Mac community for it, I was lost.

Finally, I stumbled on the Edit References window in MonoDevelop and found what I was missing. To find it:

  1. In the Project menu, select Edit References.
  2. On the Packages tab, scroll down to and select the assembly you wish to include (mine was System.Windows.Forms).
  3. Click OK.

And that’s all there is to it. My “Hello Form” project compiled just fine. It is important to note, that in order for the Edit References option to be available in the Project menu, you need to be working in an active project, or solution. When I was first trying to compile my “Hello Form” program, I had opened it as a single file and that was a mistake.

It might be best to note here also that System is another available assembly in the list. If you ever get a “missing assembly reference” error, check that list!

The code for my “Hello Form” program was very simple:

using System;
using System.Windows.Forms;

namespace HelloForm
    public class HelloForm : Form
        public static void Main()
            Application.Run(new HelloForm());