ViewController.cs

using System;
using CoreGraphics;
using UIKit;
using Foundation;
using System.Collections.Generic;
using System.Threading.Tasks;
using System.Threading;

using Zooming;
using System.IO;

namespace Zooming
{
	public partial class ViewController : UIViewController
	{

		ImageScrollView scrollView;

		public ViewController (IntPtr handle) : base (handle)
		{

		}


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

			var image = UIImage.FromFile ("images/1.jpg");
		
			var proImage = new ImageDetails ();

			//In Project we are resizing image and Image height is given image.CGImage.Height;
			proImage.Height = (float)(View.Frame.Height);//image.CGImage.Height;
			proImage.Width = (float)(View.Frame.Width);//image.CGImage.Width;
			proImage.Image = image;

			scrollView = new ImageScrollView (proImage) {
				AutoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleHeight,
			};

			zoomScale = (nfloat) Math.Min(View.Bounds.Size.Width / proImage.Image.Size.Width, 
				View.Bounds.Size.Height / proImage.Image.Size.Height);


			scrollView.MaximumZoomScale = 4f;
			scrollView.MinimumZoomScale = zoomScale;

			UITapGestureRecognizer doubletap = new UITapGestureRecognizer (OnDoubleTap) {
				NumberOfTapsRequired = 2 // double tap
			};
			scrollView.AddGestureRecognizer (doubletap);
			View = scrollView;

			scrollView.BackgroundColor = UIColor.White;
		}

		nfloat zoomScale;

			
		private void OnDoubleTap (UIGestureRecognizer gesture)
		{
			
			if (scrollView.ZoomScale >= (zoomScale * 2))
				scrollView.SetZoomScale (zoomScale, true);
			else
				scrollView.SetZoomScale (scrollView.ZoomScale * 2, true);
		}

	}
}