ParentViewController.Keyboard.cs

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

namespace TwinCoders.Utils
{
    public abstract partial class ParentViewController
    {

        /// <summary>
        /// Call this method from constructor, ViewDidLoad or ViewWillAppear to enable keyboard handling in the main partial class
        /// </summary>
        void InitKeyboardHandling()
        {
            //Only do this if required
            if (HandlesKeyboardNotifications()) {
                RegisterForKeyboardNotifications();
            }
        }

        /// <summary>
        /// Set this field to any view inside the textfield to center this view instead of the current responder
        /// </summary>
        protected UIView ViewToCenterOnKeyboardShown;
        protected UIScrollView ScrollToCenterOnKeyboardShown;

        /// <summary>
        /// Override point for subclasses, return true if you want to handle keyboard notifications
        /// to center the active responder in the scroll above the keyboard when it appears
        /// </summary>
        public virtual bool HandlesKeyboardNotifications()
        {
            return false;
        }

        NSObject _keyboardShowObserver;
        NSObject _keyboardHideObserver;
        protected virtual void RegisterForKeyboardNotifications()
        {
            if (_keyboardShowObserver == null)
                _keyboardShowObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillShowNotification, OnKeyboardNotification);
            if (_keyboardHideObserver == null)
                _keyboardHideObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillHideNotification, OnKeyboardNotification);
        }

        protected virtual void UnregisterForKeyboardNotifications()
        {
            if (_keyboardShowObserver != null)
            {
                NSNotificationCenter.DefaultCenter.RemoveObserver(_keyboardShowObserver);
                _keyboardShowObserver.Dispose();
                _keyboardShowObserver = null;
            }

            if (_keyboardHideObserver != null)
            {
                NSNotificationCenter.DefaultCenter.RemoveObserver(_keyboardHideObserver);
                _keyboardHideObserver.Dispose();
                _keyboardHideObserver = null;
            }
        }

        /// <summary>
        /// Gets the UIView that represents the "active" user input control (e.g. textfield, or button under a text field)
        /// </summary>
        /// <returns>
        /// A <see cref="UIView"/>
        /// </returns>
        protected virtual UIView KeyboardGetActiveView()
        {
            return View.FindFirstResponder();
        }

        private void OnKeyboardNotification (NSNotification notification)
        {
            if (!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 keyboardFrame = visible
                                ? UIKeyboard.FrameEndFromNotification(notification)
                                : UIKeyboard.FrameBeginFromNotification(notification);

            OnKeyboardChanged (visible, keyboardFrame);

            //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='keyboardFrame'>
        /// Frame of the keyboard
        /// </param>
        protected virtual void OnKeyboardChanged (bool visible, RectangleF keyboardFrame)
        {
            var activeView = ViewToCenterOnKeyboardShown ?? KeyboardGetActiveView();
            if (activeView == null)
                return;

            var scrollView = ScrollToCenterOnKeyboardShown ??
                             activeView.FindTopSuperviewOfType(View, typeof(UIScrollView)) as UIScrollView;
            if (scrollView == null)
                return;

            if (!visible)
                scrollView.RestoreScrollPosition();
            else
                scrollView.CenterView(activeView, keyboardFrame);
        }

        /// <summary>
        /// Call it to force dismiss keyboard when background is tapped
        /// </summary>
        protected void DismissKeyboardOnBackgroundTap()
        {
            // 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 || touch.View.FindSuperviewOfType(View, typeof(UITableViewCell)) != null);
            View.AddGestureRecognizer(tap);
        }
    }
}

ScrollExtensions.cs

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

namespace TwinCoders.Utils
{
    public static class ScrollExtensions
    {
        public static void CenterView(this UIScrollView scrollView, UIView viewToCenter, RectangleF keyboardFrame, bool animated = false) {
            var scrollFrame = scrollView.Frame;

            var adjustedFrame = UIApplication.SharedApplication.KeyWindow.ConvertRectFromView(scrollFrame, scrollView.Superview);

            var intersect = RectangleF.Intersect(adjustedFrame, keyboardFrame);

            scrollView.CenterView(viewToCenter, IsLandscape() ? intersect.Width : intersect.Height, animated:animated);
        }

        public static void CenterView(this UIScrollView scrollView, UIView viewToCenter, float keyboardHeight = 0, bool adjustContentInsets = true, bool animated = false)
        {
            if (adjustContentInsets)
            {
                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
            RectangleF relativeFrame = viewToCenter.Superview.ConvertRectToView(viewToCenter.Frame, scrollView);

            var spaceAboveKeyboard = scrollView.Frame.Height - keyboardHeight;

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

        public static void RestoreScrollPosition(this UIScrollView scrollView)
        {
            scrollView.ContentInset = UIEdgeInsets.Zero;
            scrollView.ScrollIndicatorInsets = UIEdgeInsets.Zero;
        }

        public static bool IsLandscape() {
            var orientation = UIApplication.SharedApplication.StatusBarOrientation;
            bool landscape = orientation == UIInterfaceOrientation.LandscapeLeft 
                        || orientation == UIInterfaceOrientation.LandscapeRight;
            return landscape;
        }
    }
}

ViewExtensions.cs

using System;
using MonoTouch.UIKit;

namespace TwinCoders.Utils
{
    public static class ViewExtensions
    {
        /// <summary>
        /// Find the first responder in the <paramref name="view"/>'s subview hierarchy
        /// </summary>
        /// <param name="view">
        /// A <see cref="UIView"/>
        /// </param>
        /// <returns>
        /// A <see cref="UIView"/> that is the first responder or null if there is no first responder
        /// </returns>
        public static UIView FindFirstResponder(this UIView view)
        {
            if (view.IsFirstResponder)
            {
                return view;
            }
            foreach (UIView subView in view.Subviews)
            {
                var firstResponder = subView.FindFirstResponder();
                if (firstResponder != null)
                    return firstResponder;
            }
            return null;
        }

        /// <summary>
        /// Find the first Superview of the specified type (or descendant of)
        /// </summary>
        /// <param name="view">
        /// A <see cref="UIView"/>
        /// </param>
        /// <param name="stopAt">
        /// A <see cref="UIView"/> that indicates where to stop looking up the superview hierarchy
        /// </param>
        /// <param name="type">
        /// A <see cref="Type"/> to look for, this should be a UIView or descendant type
        /// </param>
        /// <returns>
        /// A <see cref="UIView"/> if it is found, otherwise null
        /// </returns>
        public static UIView FindSuperviewOfType(this UIView view, UIView stopAt, Type type)
        {
            if (view.Superview != null)
            {
                if (type.IsInstanceOfType(view.Superview))
                {
                    return view.Superview;
                }

                if (view.Superview != stopAt)
                    return view.Superview.FindSuperviewOfType(stopAt, type);
            }

            return null;
        }

        public static UIView FindTopSuperviewOfType(this UIView view, UIView stopAt, Type type)
        {
            var superview = view.FindSuperviewOfType(stopAt, type);
            var topSuperView = superview;
            while (superview != null && superview != stopAt)
            {
                superview = superview.FindSuperviewOfType(stopAt, type);
                if (superview != null)
                    topSuperView = superview;

            }
            return topSuperView;
        }
    }

}