When implementing touch and gesture based interaction in your application, for example the swipe effect, you had to handle the TouchesMoved, TouchesBegan, TouchesEnded and TouchesCancelled events and handle the location of the finger and last location and so on, based on the quality of the algorithm it worked or not.

With the new SDK and with the great support from MonoTouch team, its current version of MonoTouch implements the UIGestureRecognizer and UIGestureRecognizerDelegate and related classes - UITapGestureRecognizer, UISwipeGestureRecognizer, UIRotationGestureRecognizer, UIPinchGestureRecognizer, UILongPressGestureRecognizer, UIPanGestureRecognizer. Lets have a look and few simple steps to take advantage of these common gesture implementations on the iPhone/iPad. For the demonstration we will use the swipe gesture.

First we need to have a view controller and define a Selector for the gesture recognizer. More on Selectors check the iPhone SDK, in general it is a special form of message. In MonoTouch Selectors can be consumed (fired from MonoTouch code) or exposed, being available to SDK functions and classes to be called from within.

Lets have a look at the typical implementation:

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public partial class MyViewController : UIViewController
	{
		public static Selector MySelector
		{
			get 
			{
				return new Selector("HandleSwipe");
			}
		}
///
/// and other class definition
///
	}

Please note that the Selector is defined as a static access property returning the identification of the selector via its name (HandleSwipe).

Next we need to define the gesture recognizer and its delegate and assign it to the view. We do this in the ViewDidLoad event of the controller implementation class.

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// define the gesture recognizer 
MonoTouch.UIKit.UISwipeGestureRecognizer sgr = new MonoTouch.UIKit.UISwipeGestureRecognizer();
 
// add the target to it, we put the instance itself of the controller 
// and the class instance selector
sgr.AddTarget(this, MainComicsViewController.MySelector);

// add the swipe direction, there are 4 of them (left, right, up, down). If other than one swipe is 
// needed then more recognizers must be defined and added to the view - each for the direction
sgr.Direction = UISwipeGestureRecognizerDirection.Left; 

// also assign the delegate
sgr.Delegate = new SwipeRecognizerDelegate();
 
// and last, add the recognizer to this view to take actions
this.View.AddGestureRecognizer(sgr);

Then we need our delegate class for the swipe recognizer:

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public class SwipeRecognizerDelegate : MonoTouch.UIKit.UIGestureRecognizerDelegate
	{
		public override bool ShouldReceiveTouch(UIGestureRecognizer recognizer, UITouch touch)
		{
			return true;
		}
	}

And last and finally our handler for the swipe event:

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[Export("HandleSwipe")]
public void HandleSwipe(UISwipeGestureRecognizer recognizer)
{
	// get the point of the swipe action
	PointF point = recognizer.LocationInView(this.View);
 
	// TODO: do something with the swipe
}

Well, that is all and we are done.

Happy coding!