NET-MEF Programming in Visual C# 2010 Express:Hosting MEF in an Application - 2 errors

Question

Hi all,

I copied the following code from the Microsoft .NET MEF website:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel.Composition;
using System.ComponentModel.Composition.Hosting;
using System.Reflection;
namespace scNET_MEF_1
{
 [Import]
  public IMessageSender MessageSender { get; set; }
    class Program
    {
        static void Main(string[] args)
        {
            Program p = new Program();
            p.Run();
        }
        public void Run()
        {
            Compose();
            MessageSender.Send("Message Sent");
        }
        private void Compose()
        {
            AssemblyCatalog catalog = new AssemblyCatalog(Assembly.GetExecutingAssembly());
            var container = new CompositionContainer(catalog);
            container.ComposeParts(this);
        }
    }
    public interface IMessageSender
    {
        void Send(string message);
    }
    [Export(typeof(IMessageSender))]
    public class EmailSender : IMessageSender
    {
        public void Send(string message)
        {
            Console.WriteLine(message);
        }
    }
}

I got the following 2 errors: 1 Error Expected class, delegate, enum, interface, or struct C:\Documents and Settings\e1enxshc\Local Settings\Application Data\Temporary Projects\scNET_MEF_1\Program.cs 12 10 scNET_MEF_1
2 Error The name 'MessageSender' does not exist in the current context C:\Documents and Settings\e1enxshc\Local Settings\Application Data\Temporary Projects\scNET_MEF_1\Program.cs 23 13 scNET_MEF_1

Please kindly help and advise me what causes the errors and how to correct the errors.

Thanks in advance,

Scott Chang

Answer 1

Your property needs to be inside the class:

namespace scNET_MEF_1
{
 // This can't be outside of the class - move it
 // [Import]
 //  public IMessageSender MessageSender { get; set; }

    class Program
    {
        // Move this inside of the class!
        [Import]
        public IMessageSender MessageSender { get; set; }

        static void Main(string[] args)
        {
            Program p = new Program();
            p.Run();
        }

---

Reed Copsey, Jr. - http://reedcopsey.com
If a post answers your question, please click "Mark As Answer" on that post and "Mark as Helpful".

Answer 2

Hi Reed, Thanks for your valuable response.

After I these 2 code statments to the right place, it worked nicely. But the console screen flashed quickly and I could see the console screen.  How can I make the console screen stay on for a little longer?  I added

 public void Run()
        {
            Compose();
            MessageSender.Send("Message Sent");
            Console.WriteLine(MessageSender);  //I added in order to make the console screen stay on longer!!!
            Console, ReadKey();           //I added in order to make the console screen stay on longer!!!
        }

I got the following errors: 1 Error Only assignment, call, increment, decrement, and new object expressions can be used as a statement C:\Documents and Settings\e1enxshc\Local Settings\Application Data\Temporary Projects\scNET_MEF_1\Program.cs 32 13 scNET_MEF_1
2 Error 'System.Console' is a 'type' but is used like a 'variable' C:\Documents and Settings\e1enxshc\Local Settings\Application Data\Temporary Projects\scNET_MEF_1\Program.cs 32 13 scNET_MEF_1
3 Error The name 'ReadKey' does not exist in the current context C:\Documents and Settings\e1enxshc\Local Settings\Application Data\Temporary Projects\scNET_MEF_1\Program.cs 32 22 scNET_MEF_1
4 Error Invalid expression term ',' C:\Documents and Settings\e1enxshc\Local Settings\Application Data\Temporary Projects\scNET_MEF_1\Program.cs 32 20 scNET_MEF_1
5 Error ; expected C:\Documents and Settings\e1enxshc\Local Settings\Application Data\Temporary Projects\scNET_MEF_1\Program.cs 32 20 scNET_MEF_1
6 Error ; expected C:\Documents and Settings\e1enxshc\Local Settings\Application Data\Temporary Projects\scNET_MEF_1\Program.cs 32 22 scNET_MEF_1

Please help and advise me how to make the console screen stay on a little longer.

Thannks again,

Scott Chang

Answer 3

You need to use

Console.ReadKey();

Not:

Console, ReadKey(); 

(Note that yours has a comma, not a period)

---

Reed Copsey, Jr. - http://reedcopsey.com
If a post answers your question, please click "Mark As Answer" on that post and "Mark as Helpful".