DLL Injection in C#

Question

DLL

I wrote a C# program that injects a DLL into a workflow.

But the problem is that the DLL (also written in C #) is injected, but the message does not show.
Do not tell me what could be the problem?

DLL code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices; 

namespace MyDll
{
  public class Class1
  {
    public void Main()
    {
      while (true)
      {
        MessageBox.Show("Hello world!");
      }
    } 
  }
}

If you need I can also add the loader code.!