Scroll Content when soft keyboard appears/disappears in iOS UIViewController

AutoScrollFromKeyboard.cs

using System;
using CoreGraphics;
using Foundation;
using HakiOS.Ui.Extensions;
using UIKit;

// adapted from http://forums.xamarin.com/discussion/comment/23235/#Comment_23235
namespace HakiOS.Ui.Utils
{
	public class AutoScrollFromKeyboard
	{
		public UIView ViewToCenterOnKeyboardShown { get; set; }

		private UIViewController _controller;
		private NSObject _willHideObserver;
		private NSObject _willShowObserver;

		public AutoScrollFromKeyboard(UIViewController controller, 
			bool dismissKeyboardOnBackgroundTap = true, 
			UIView viewToCenterOnKeyboardShown = null)
		{
			_controller = controller;
			ViewToCenterOnKeyboardShown = viewToCenterOnKeyboardShown;

			if(dismissKeyboardOnBackgroundTap)
				_controller.View.DismissKeyboardOnTap();

			RegisterForKeyboardNotifications();
		}

		private void RegisterForKeyboardNotifications()
		{
			_willHideObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillHideNotification, OnKeyboardNotification);
			_willShowObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillShowNotification, OnKeyboardNotification);
		}

		private void OnKeyboardNotification(NSNotification notification)
		{
			if (!_controller.IsViewLoaded) return;

			//Check if the keyboard is becoming visible
			var visible = notification.Name == UIKeyboard.WillShowNotification;

			//Start an animation, using values from the keyboard
			UIView.BeginAnimations("AnimateForKeyboard");
			UIView.SetAnimationBeginsFromCurrentState(true);
			UIView.SetAnimationDuration(UIKeyboard.AnimationDurationFromNotification(notification));
			UIView.SetAnimationCurve((UIViewAnimationCurve)UIKeyboard.AnimationCurveFromNotification(notification));

			//Pass the notification, calculating keyboard height, etc.
			var landscape = _controller.InterfaceOrientation == UIInterfaceOrientation.LandscapeLeft 
				|| _controller.InterfaceOrientation == UIInterfaceOrientation.LandscapeRight;

			var keyboardFrame = visible
				? UIKeyboard.FrameEndFromNotification(notification)
				: UIKeyboard.FrameBeginFromNotification(notification);

			OnKeyboardChanged(visible, landscape ? keyboardFrame.Width : keyboardFrame.Height);

			//Commit the animation
			UIView.CommitAnimations();
		}

		/// <summary>
		/// Override this method to apply custom logic when the keyboard is shown/hidden
		/// </summary>
		/// <param name='visible'>
		/// If the keyboard is visible
		/// </param>
		/// <param name='keyboardHeight'>
		/// Calculated height of the keyboard (width not generally needed here)
		/// </param>
		protected virtual void OnKeyboardChanged(bool visible, nfloat keyboardHeight)
		{
			var activeView = ViewToCenterOnKeyboardShown ?? _controller.View.FindFirstResponder();
			var scrollView = activeView?.FindSuperviewOfType(_controller.View, typeof(UIScrollView)) as UIScrollView;

			if (scrollView == null)
				return;

			if (!visible)
				RestoreScrollPosition(scrollView);
			else
				CenterViewInScroll(activeView, scrollView, keyboardHeight);
		}

		protected virtual void CenterViewInScroll(UIView viewToCenter, UIScrollView scrollView, nfloat keyboardHeight)
		{
			var contentInsets = new UIEdgeInsets(0.0f, 0.0f, keyboardHeight, 0.0f);
			scrollView.ContentInset = contentInsets;
			scrollView.ScrollIndicatorInsets = contentInsets;

			// Position of the active field relative isnside the scroll view
			var relativeFrame = viewToCenter.Superview.ConvertRectToView(viewToCenter.Frame, scrollView);

			var landscape = _controller.InterfaceOrientation == UIInterfaceOrientation.LandscapeLeft 
				|| _controller.InterfaceOrientation == UIInterfaceOrientation.LandscapeRight;

			var spaceAboveKeyboard = (landscape ? scrollView.Frame.Width : scrollView.Frame.Height) - keyboardHeight;

			// Move the active field to the center of the available space
			var offset = relativeFrame.Y - (spaceAboveKeyboard - viewToCenter.Frame.Height) / 2;
			scrollView.ContentOffset = new CGPoint(0, offset);
		}

		protected virtual void RestoreScrollPosition(UIScrollView scrollView)
		{
			scrollView.ContentInset = UIEdgeInsets.Zero;
			scrollView.ScrollIndicatorInsets = UIEdgeInsets.Zero;
		}

		public void Dispose()
		{
			if(_willHideObserver != null)
				NSNotificationCenter.DefaultCenter.RemoveObserver(_willHideObserver);

			if(_willShowObserver != null)
				NSNotificationCenter.DefaultCenter.RemoveObserver(_willShowObserver);

			_controller = null;
			ViewToCenterOnKeyboardShown = null;
		}
	}
}

ViewExtensions.cs

using System;
using System.Linq;
using UIKit;

namespace HakiOS.Ui.Extensions
{
	public static class ViewExtensions
	{
		/// <summary>
		/// Will hide soft keyboard when tapping on this view
		/// </summary>
		public static void DismissKeyboardOnTap(this UIView view)
		{
			// Add gesture recognizer to hide keyboard
			var tap = new UITapGestureRecognizer { CancelsTouchesInView = false };
			tap.AddTarget(() => view.EndEditing(true));
			tap.ShouldReceiveTouch = (recognizer, touch) => !(touch.View is UIControl);

			view.AddGestureRecognizer(tap);
		}
	}
}