Castle Dynamic Proxy Example

Freezable.cs

using System;
using System.Collections.Generic;
using Castle.DynamicProxy.Generators;
using Castle.DynamicProxy;

// http://kozmic.net/2008/12/16/castle-dynamicproxy-tutorial-part-i-introduction/

public interface IFreezable
{
	bool IsFrozen { get; }
	void Freeze();
}

public static class Freezable
{
	public static readonly IDictionary<object, IFreezable> _freezables = new Dictionary<object, IFreezable>();

	private static readonly ProxyGenerator _generator = new ProxyGenerator();

	public static bool IsFreezable(object obj)
	{
		return obj != null && _freezables.ContainsKey(obj);
	}

	public static void Freeze(object freezable)
	{
		if (!IsFreezable(freezable))
		{
			throw new System.Exception("not freezable object: " + freezable.GetHashCode());
		}
		_freezables[freezable].Freeze();
	}

	public static bool IsFrozen(object freezable)
	{
		return IsFreezable(freezable) && _freezables[freezable].IsFrozen;
	}

	public static T MakeFreezable<T>() where T : class, new()
	{
		var interceptor = new FreezableInterceptor();
		var proxy = _generator.CreateClassProxy<T>(new CallLoggingInterceptor(), interceptor);
		_freezables.Add(proxy, interceptor);
		return proxy;
	}
}

public class CallLoggingInterceptor : IInterceptor
{
	private int indentation;

	public void Intercept(IInvocation invocation)
	{
		try
		{
			indentation++;
			Console.WriteLine(string.Format("{0} ! {1}", new string(' ', indentation), invocation.Method.Name));
			invocation.Proceed();
		}
		finally
		{
			indentation--;
		}
	}
}

public class FreezableInterceptor : IInterceptor, IFreezable
{
	private bool _isFrozen;

	public bool IsFrozen
	{
		get
		{
			return _isFrozen;
		}
	}

	public void Freeze()
	{
		_isFrozen = true;
	}

	public void Intercept(IInvocation invocation)
	{
		if (_isFrozen && invocation.Method.Name.StartsWith("set_", StringComparison.OrdinalIgnoreCase))
		{
			throw new Exception("Object Frozen");
		}
		invocation.Proceed();
	}
}

public class Person
{
	public virtual string FirstName { get; set; }
	public virtual string LastName { get; set; }

	public override string ToString()
	{
		return FirstName + " " + LastName;
	}
}

class Program
{
	static void Main(string[] args)
	{
		Person p = Freezable.MakeFreezable<Person>();
		p.FirstName = "Foo";
		p.LastName = "Bar";
		Console.WriteLine(p);
		Freezable.Freeze(p);
		p.FirstName = "what";
		Console.WriteLine(p);
	}
}