Xamarin swizzle

XamarinSwizzle.cs

using System;
using System.Runtime.InteropServices;
using MonoTouch.ObjCRuntime;
using MonoTouch.Foundation;

namespace XamarinSwizzle
{
	[Register("TestClass")]
	public class TestCode : NSObject
	{
		public TestCode() : base()
		{
		}

		static TestCode()
		{
			ExchangeMethods();
		}

		public void Run()
		{
			objc_msgSend(this.Handle, Selector.GetHandle("layoutSubviews"));
			objc_msgSend(this.Handle, Selector.GetHandle("myLayoutSubviews"));
		}

		[DllImport ("/usr/lib/libobjc.dylib", EntryPoint = "method_exchangeImplementations")]
		private static extern void method_exchangeImplementations (IntPtr existingMethod, IntPtr newMethod);

		[DllImport ("/usr/lib/libobjc.dylib", EntryPoint = "class_getInstanceMethod")]
		private static extern IntPtr class_getInstanceMethod (IntPtr classHandle, IntPtr selectorHandle);

		[DllImport ("/usr/lib/libobjc.dylib", EntryPoint = "objc_msgSend")]
		private static extern void objc_msgSend (IntPtr receiver, IntPtr selector);

		private static void ExchangeMethods()
		{
			var classHandle = Class.GetHandle("TestClass");

			var s1 = Selector.GetHandle("layoutSubviews");
			var s2 = Selector.GetHandle("myLayoutSubviews");

			var m1 = class_getInstanceMethod(classHandle, s1);
			var m2 = class_getInstanceMethod(classHandle, s2);

			// this won't work since http://forums.xamarin.com/discussion/comment/51694/#Comment_51694
			method_exchangeImplementations(m1, m2);
		}

		[Export("myLayoutSubviews")]
		private void myLayoutSubviews()
		{
			Console.WriteLine("myLayoutSubviews");
		}

		[Export("layoutSubviews")]
		private void layoutSubviews()
		{
			Console.WriteLine("layoutSubviews");
		}

	}
}

Another implementation
https://github.com/dbeattie71/TLYShyNavBar.iOS/blob/master/TLYShyNavBar.iOS/TLYShyNavBarManager.m.cs