Question

I created a Console application which searches for plugins ending with PlugIn.dll.
It loads the dll assembly and executes the write method of plugInClass in PlugIn.dll.
I created an interface called IWrite which includes the write method.
After executing the console app,it gives an error as given below:

Unable to cast object of type ‘HPlugIn.plugInClass’ to type ‘ConsolePlugIn.IWrite’.

Here is my code for console app..[Main application]

using System;
using System.IO;
using System.Reflection;
namespace ConsolePlugIn
{
    interface IWrite
    {
        void write();
    }
    class Program
    {
        static void Main(string[] args)
        {
            foreach (string s in Directory.GetFiles(AppDomain.CurrentDomain.BaseDirectory, "*PlugIn.dll"))//getting plugins in base directory
            {
                Assembly aWrite = Assembly.LoadFrom(s);
                Type tWrite = aWrite.GetType("HPlugIn.plugInClass");
                IWrite click = (IWrite)Activator.CreateInstance(tWrite);//giving casting error
                click.write();
            }
        } 
    }
}

here is my code for the plugIn dll file

using System;
namespace HPlugIn
{
    interface IWrite
    {
        void write();
    }
    public class plugInClass : IWrite
    {
      public  void write()
        {
            Console.Write("High from plugInClass");
        }
    }
}

Any idea for this casting error?
Thanks in advance!

Answer 1

The IWrite interfaces in the EXE and in the DLL are not the same, even though their structures are identical. You need to make a third dll with the interface, and share it among the DLLs and the EXE.

Common:

namespace Shared {
    interface IWrite {
        void write();
    }
}

DLL:

using System;
using Shared;
namespace HPlugIn {
    public class plugInClass : IWrite {
        public  void write() {
            Console.Write("High from plugInClass");
        }
    }
}

EXE:

using System;
using System.IO;
using System.Reflection;
using Shared;
namespace ConsolePlugIn {
    class Program {
        ...
    } 
}