Example code showing how to use [Easy Layout](http://praeclarum.org/post/45690317491/easy-layout-a-dsl-for-nslayoutconstraint).

LayoutViewController.cs

using System;
using MonoTouch.UIKit;
using System.Drawing;

namespace Async.iOS
{
    public class LayoutViewController : UIViewController
	{
		UITextField text;
		UIButton button;

		const float ButtonWidth = 88;
		const float HPadding = 22;
		const float VPadding = 44;

		public override void ViewDidLoad ()
		{
			base.ViewDidLoad ();

			View.BackgroundColor = UIColor.White;

			text = new UITextField {
				Placeholder = "Search",
				BorderStyle = UITextBorderStyle.RoundedRect,
			};

			button = UIButton.FromType (UIButtonType.RoundedRect);
			button.SetTitle ("Search", UIControlState.Normal);

			View.AddSubviews (text, button);

//			LayoutWithSpringsAndStruts ();
//			LayoutWithConstraints ();
			LayoutWithEase ();
		}

		void LayoutWithSpringsAndStruts ()
		{
			var b = View.Bounds;

			button.Frame = new RectangleF (
				b.Width - HPadding - ButtonWidth,
				VPadding,
				ButtonWidth,
				44);
			button.AutoresizingMask =
				UIViewAutoresizing.FlexibleLeftMargin |
				UIViewAutoresizing.FlexibleBottomMargin;

			text.Frame = new RectangleF (
				HPadding,
				VPadding,
				b.Width - ButtonWidth - 3 * HPadding,
				text.Font.PointSize + 14);
			text.AutoresizingMask =
				UIViewAutoresizing.FlexibleWidth |
				UIViewAutoresizing.FlexibleBottomMargin;
		}

		void LayoutWithConstraints ()
		{
			button.TranslatesAutoresizingMaskIntoConstraints = false;

			// Set button width
			View.AddConstraint (NSLayoutConstraint.Create (
				button, NSLayoutAttribute.Width,
				NSLayoutRelation.Equal,
				null, NSLayoutAttribute.NoAttribute,
				0, ButtonWidth));
			
			// Set button top
			View.AddConstraint (NSLayoutConstraint.Create (
				button, NSLayoutAttribute.Top,
				NSLayoutRelation.Equal,
				View, NSLayoutAttribute.Top,
				1, VPadding));

			// Set button right
			View.AddConstraint (NSLayoutConstraint.Create (
				button, NSLayoutAttribute.Right,
				NSLayoutRelation.Equal,
				View, NSLayoutAttribute.Right,
				1, -HPadding));

			text.TranslatesAutoresizingMaskIntoConstraints = false;

			// Set text left
			View.AddConstraint (NSLayoutConstraint.Create (
				text, NSLayoutAttribute.Left,
				NSLayoutRelation.Equal,
				View, NSLayoutAttribute.Left,
				1, HPadding));

			// Set text right
			View.AddConstraint (NSLayoutConstraint.Create (
				text, NSLayoutAttribute.Right,
				NSLayoutRelation.Equal,
				button, NSLayoutAttribute.Left,
				1, -HPadding));

			// Set text top
			View.AddConstraint (NSLayoutConstraint.Create (
				text, NSLayoutAttribute.Top,
				NSLayoutRelation.Equal,
				button, NSLayoutAttribute.Top,
				1, 0));
		}

		void LayoutWithEase ()
		{
			View.ConstrainLayout (() => 
				button.Frame.Width == ButtonWidth &&
				button.Frame.Right == View.Frame.Right - HPadding &&
				button.Frame.Top == View.Frame.Top + VPadding &&

				text.Frame.Left == View.Frame.Left + HPadding &&
				text.Frame.Right == button.Frame.Left - HPadding &&
				text.Frame.Top == button.Frame.Top
			);
		}
	}
}

Do you know why this sample viewController would stop working in a Nav controller? It I chose the springs and struts it works perfectly, if I do the auto-layout the background goes black and the constraints related to the superview fail.