MyMasterPageRenderer.cs

using System;
using Xamarin.Forms.Platform.iOS;
using Xamarin.Forms;
using SplitTest;
using SplitTest.iOS;
using MonoTouch.UIKit;

[assembly:ExportRenderer(typeof(MyMasterPage), typeof(MyMasterPageRenderer))]

namespace SplitTest.iOS
{
	public class MyMasterPageRenderer : TabletMasterDetailRenderer
	{
		protected override void OnElementChanged (VisualElementChangedEventArgs e)
		{
			base.OnElementChanged (e);

			Console.WriteLine ("In renderer");

			var split = (UISplitViewController)this;
			split.MinimumPrimaryColumnWidth = 270;
			split.MaximumPrimaryColumnWidth = 600;
		}
	}
}