卸载c#中的外部类库

可能重复：
从AppDomain卸载.DLL所需的帮助-即使使用ShadowCopy 也无法工作

在我的项目中，我使用MEF框架来提供可扩展性；主程序可以通过另一个Lib.dll类库进行扩展。

问题是，我需要在不关闭主程序的情况下将此Lib.dll与另一个进行交换。

那么，我如何卸载这个Lib.dll来交换它呢？

更新

主程序的形式是：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel.Composition;
using System.ComponentModel.Composition.Hosting;
namespace SimpleCalculator3
{
    public interface ICalculator
    {
        String Calculate(String input);
    }
    public interface IOperation
    {
        int Operate(int left, int right);
    }
    public interface IOperationData
    {
        Char Symbol { get; }
    }
    [Export(typeof(IOperation))]
    [ExportMetadata("Symbol", '+')]
    class Add : IOperation
    {
        public int Operate(int left, int right)
        {
            return left + right;
        }
    }
    [Export(typeof(IOperation))]
    [ExportMetadata("Symbol", '-')]
    class Subtract : IOperation
    {
        public int Operate(int left, int right)
        {
            return left - right;
        }
    }

    [Export(typeof(ICalculator))]
    class MySimpleCalculator : ICalculator
    {
        [ImportMany]
        IEnumerable<Lazy<IOperation, IOperationData>> operations;
        public String Calculate(String input)
        {
            int left;
            int right;
            Char operation;
            int fn = FindFirstNonDigit(input); //finds the operator
            if (fn < 0) return "Could not parse command.";
            try
            {
                //separate out the operands
                left = int.Parse(input.Substring(0, fn));
                right = int.Parse(input.Substring(fn + 1));
            }
            catch
            {
                return "Could not parse command.";
            }
            operation = input[fn];
            foreach (Lazy<IOperation, IOperationData> i in operations)
            {
                if (i.Metadata.Symbol.Equals(operation)) return i.Value.Operate(left, right).ToString();
            }
            return "Operation Not Found!";
        }
        private int FindFirstNonDigit(String s)
        {
            for (int i = 0; i < s.Length; i++)
            {
                if (!(Char.IsDigit(s[i]))) return i;
            }
            return -1;
        }

    }

    class Program
    {
        private CompositionContainer _container;
        [Import(typeof(ICalculator))]
        public ICalculator calculator;

        private Program()
        {
            //An aggregate catalog that combines multiple catalogs
            var catalog = new AggregateCatalog();
            //Adds all the parts found in the same assembly as the Program class
            catalog.Catalogs.Add(new AssemblyCatalog(typeof(Program).Assembly));
            //catalog.Catalogs.Add(new DirectoryCatalog("C:''Users''SomeUser''Documents''Visual Studio 2010''Projects''SimpleCalculator3''SimpleCalculator3''Extensions"));

            //Create the CompositionContainer with the parts in the catalog
            _container = new CompositionContainer(catalog);
            //Fill the imports of this object
            try
            {
                this._container.ComposeParts(this);
            }
            catch (CompositionException compositionException)
            {
                Console.WriteLine(compositionException.ToString());
            }
        }

        static void Main(string[] args)
        {
            Program p = new Program(); //Composition is performed in the constructor
            String s;
            Console.WriteLine("Enter Command:");
            while (true)
            {
                s = Console.ReadLine();
                Console.WriteLine(p.calculator.Calculate(s));
            }

        }
    }
}

并且扩展Lib.dll的形式是

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel.Composition;
namespace ExtendedOperations {
    [Export(typeof(SimpleCalculator3.IOperation))]
    [ExportMetadata("Symbol", '%')]
    public class Mod : SimpleCalculator3.IOperation
    {
        public int Operate(int left, int right)
        {
            return left % right;
        }
    }
}

也就是说，我想动态地更改Lib.dll中的代码，并在主程序运行时构建它

AppDomainSetup ads = new AppDomainSetup();
ads.PrivateBinPath = Path.GetDirectoryName("C:''some.dll");
AppDomain ad2 = AppDomain.CreateDomain("AD2", null, ads);
ProxyDomain proxy = (ProxyDomain)ad2.CreateInstanceAndUnwrap(typeof(ProxyDomain).Assembly.FullName, typeof(ProxyDomain).FullName);
bool ok = proxy.LoadDll("C:''some.dll");
AppDomain.Unload(ad2);
public class ProxyDomain : MarshalByRefObject
{
    public bool LoadDll(string assemblyPath)
    {
         Assembly myDLL = Assembly.LoadFile(assemblyPath);
        //use your dll here
    }
}