C# Instantiate Class from String given an Interface

I am trying to make an instance of a class based on a string that will be retrieved from the User Interface, and then I want to access the properties of the instance of the class.

Here is an overview of what I have so far -

namespace MamdaAdapter
{
    public interface IExchange
    {
        string GetTransport();
    }
}


namespace MamdaAdapter
{
    public class Exchange
    {
        public class Arca : IExchange
        {
            private const string _Transport = "tportname";

            public string GetTransport()
            {
                return _Transport;
            }
        }


        public static IExchange DeriveExchange(string ExchangeName)
        {
            IExchange SelectedExchange = (IExchange)Activator.CreateInstance(Type.GetType(ExchangeName));

            return SelectedExchange;
        }
    }
}



namespace MyUserInterface
{
    public class MainForm
    {
        private void simpleButton1_Click(object sender, EventArgs e)
        {
            IExchange SelectedExchange = Exchange.DeriveExchange("Exchange.Arca");

            Console.WriteLine(SelectedExchange.GetTransport());
        }
    }
}

UPDATE: Right now, I'm getting an Exception that says t开发者_如何学Che "Value cannot be null" which to me means that it is unable to create the instance of the class given the string provided -

The problem here is how you specify the name of your class:

First, specify the namespace. Second, since Arca is an inner class you must use '+' instead of '.'

(...) = Exchange.DeriveExchange("MamdaAdapter.Exchange+Arca");

Assuming you UI doesnt expose the full type name, you typically want a dictionary to associate the display name to the type:

Dictionary<string, Type> _associations = new Dictionary<string, Type>(); 

Then, you simply instantiate the new object:

if(_associations.ContainsKey(someString))
{
   Type selectedType = _associations[someString];

   return Activator.CreateInstance(selectedType) as IExchange;
}

throw new ApplicationException("No type defined for that string yo");

If the string is not known at compile time, you basically need to check for the existance of the type:

var type = Type.GetType(someString);

if(type != null)
{
    // Do Stuff
}

I wrote a small c# console application to simulate your need, tested ok, hope it helps:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MamdaAdapter;
using System.Reflection;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            IExchange SelectedExchange = Exchange.DeriveExchange("MamdaAdapter.Arca");
            Console.WriteLine(SelectedExchange.GetTransport());
        }
    }
}

namespace MamdaAdapter
{
    public interface IExchange
    {
        string GetTransport();
    }
}


namespace MamdaAdapter
{
    public class Arca : IExchange
    {
        private const string _Transport = "tportname";

        public string GetTransport()
        {
            return _Transport;
        }
    }
}

namespace MamdaAdapter
{
    public class Exchange
    {
        public static IExchange DeriveExchange(string ExchangeName)
        {
            IExchange SelectedExchange = (IExchange)Assembly.GetAssembly(typeof(IExchange)).CreateInstance(ExchangeName, false, BindingFlags.CreateInstance, null, null, null, null);
            return SelectedExchange;
        }
    }

}

If the Type you are looking for is not defined in the same assembly that is executing Type.GetType you must use the AssemblyQualifiedName (something like MyNamespace.MyClass, MyAssembly, Version=1.3.0.0, Culture=neutral, PublicKeyToken=b17a5c561934e089), even the FullName is not enough. Otherwise you could first get the assembly containing the class and then execute the GetType method of the Assembly class.