.net remoting accross App Domain

下面这个例子介绍了如何利用.net remoting 来实现App Domain间的访问，而且通过创建一个新的App Domain来加载一些untrusted的dlls，保证了程序自身的App Domain的边界安全。
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下面是程序的main函数：
namespace Microsoft.Samples.Application
{
    static class Program
    {
        static void Main()
        {
            //Create new appDomain
            AppDomain domain = AppDomain.CreateDomain("NewAppDomain");

            // Create remote object in new appDomain via shared interface
            // to avoid loading the implementation library into this appDomain
            IHelloWorld proxy = 
                (IHelloWorld)domain.CreateInstanceAndUnwrap(
                    "ImplementationLibrary", 
                    "Microsoft.Samples.ImplementationLibrary.HelloWorld");

            // Output results of the call
            Console.WriteLine("\nReturn:\n\t{0}", proxy.Echo("Hello"));
            Console.WriteLine();

            Console.WriteLine("Non-GAC assemblies loaded in {0} appDomain:", AppDomain.CurrentDomain.FriendlyName);
            foreach (Assembly assembly in AppDomain.CurrentDomain.GetAssemblies())
            {
                if (!assembly.GlobalAssemblyCache)
                {
                    Console.WriteLine("\t" + assembly.GetName().Name);
                }
            }
            Console.WriteLine("\nImplementationLibrary should not be loaded.");

            Console.ReadLine();
        }
    }
}

下面是被load进新创建的Domain的dll：

namespace Microsoft.Samples.ImplementationLibrary
{
    internal class HelloWorld : MarshalByRefObject, IHelloWorld
    {

        #region IHelloWorld Members

        string IHelloWorld.Echo(string input)
        {
            ConsoleColor originalColor = Console.BackgroundColor;
            Console.BackgroundColor = ConsoleColor.Blue;

            string currentAppDomainName = AppDomain.CurrentDomain.FriendlyName;
            Console.WriteLine("AppDomain: {0}", currentAppDomainName);
            Console.WriteLine("Echo Input: {0}", input);
            Console.WriteLine();
            Console.WriteLine("Non-GAC assemblies loaded in {0} appDomain:", AppDomain.CurrentDomain.FriendlyName);
            foreach (Assembly assembly in AppDomain.CurrentDomain.GetAssemblies())
            {
                if (!assembly.GlobalAssemblyCache)
                {
                    Console.WriteLine("\t" + assembly.GetName().Name);
                }
            }


            Console.BackgroundColor = originalColor;

            
            return input + " from AppDomain: " + currentAppDomainName;

        }

        #endregion

    }
}
程序的输出结果是：
AppDomain: NewAppDomain
Echo Input: Hello

Non-GAC assemblies loaded in NewAppDomain appDomain:
 ImplementationLibrary
 SharedInterface

Return:
 Hello from AppDomain: NewAppDomain

Non-GAC assemblies loaded in Application.vshost.exe appDomain:
 vshost
 Application
 SharedInterface

ImplementationLibrary should not be loaded.

另外解释一下Unwarp()函数的作用，例如ObjectHandleAssembly有一个MyType的类：
// Creates an instance of MyType defined in the assembly called ObjectHandleAssembly.
ObjectHandle obj = domain.CreateInstance("ObjectHandleAssembly", "MyType");

// Unwrapps the proxy to the MyType object created in the other AppDomain.
MyType testObj = (MyType)obj.Unwrap();