Question

Problem – I am trying my hand at plugIn development and all is going well except where trying to cast object A to object B even though A implements B.

Interface:

namespace DynamicApplications
{
    public interface IPlugIn
    {
        string Name { get; set; }
        IPlugInHost myHost { set; }
        void Show();
    }

    public interface IPlugInHost
    {
        bool Register(IPlugIn plug);
    }
}

Class which Implements IPlugIn

namespace plugInOne
{
    class PlugIn : IPlugIn
    {
        IPlugInHost _myHost;

        public string Name
        {
            get
            {
                return "Plug-In One";
            }
            set
            {
            }
        }

        public IPlugInHost myHost
        {
            set
            {
                _myHost = value;
            }
        }

        public void Show()
        {
        }
    }
}

And now THE CODE for the instantiation:

        String path = Application.StartupPath;
        string[] assemblyNames = Directory.GetFiles(path, "*.dll");
        plugs = new IPlugIn[assemblyNames.Length];

        for(int i = 0; i < assemblyNames.Length; i++)
        {
            string Name = assemblyNames[i];
            Name = Name.Substring(Name.LastIndexOf("\\") + 1, Name.Length - Name.LastIndexOf("\\") - 1);
            Name = Name.Remove(Name.LastIndexOf(".dll"));
            assemblyNames[i] = Name;
        }

        for (int i = 0; i < assemblyNames.Length; i++)
        {
            Assembly DLL = Assembly.Load(assemblyNames[i]);

            if(DLL != null)
            {
                try
                {
                    Object p = Activator.CreateInstance(DLL.GetType(assemblyNames[i] + ".PlugIn"));

                    if (p is DynamicApplications.IPlugIn)
                    {
                        MessageBox.Show("YES!!!!");
                    }
                    else
                    {
                        MessageBox.Show("no>?>?>>><<?????");
                    }

                    plugs[i] = (IPlugIn)p;
                }
                catch(Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }
        }

Note the debugger shows that p is in fact instantiated and accessible

The Application always hits MessageBox.Show("no>?>?>>><<?????");

Help Please

Aiden

EDIT

P is of Type:

Also

YET plugInOne.PlugIn implements IPlugIn

Answer 1

Your referencing a DynamicApplications.IPlugIn and that is not the same interface which will be contained in the assembly.

You need to get your IPlugin instance from your assembly instead of using a local instance. Your code for checking is fine, if you did something like this:

public interface IA { }
public class A :IA { }


object a = Activator.CreateInstance<A>();
if (a is IA)
    Console.WriteLine("Yes");

However you are getting your A (in the above context) from somewhere else, and still trying to reference your local version of IA – therefore you need to get your interface from your assembly instead of trying to reference it locally. Perhaps you could do something like this:

if (objA.GetType().GetInterfaces().Any(x => x.Name == "IA"))
  Console.WriteLine("Yes");