A UIVIew class to detect swipes, and forward the message on to a delegate which can react to the swipe

SwipeView.h

#import <UIKit/UIKit.h>

@protocol SwipeViewDelegate;

@interface SwipeView : UIView {
  id <SwipeViewDelegate> swipeDelegate;
  int touchBeganX, touchBeganY;
  int touchMovedX, touchMovedY;
}

@property (nonatomic, retain) id swipeDelegate;
@end

@protocol SwipeViewDelegate <NSObject>
- (void)viewDidSwipeLeft:(SwipeView *)swipeView;
- (void)viewDidSwipeRight:(SwipeView *)swipeView;
@end

SwipeView.m

// Swipe detection snagged from here: http://www.dosomethinghere.com/2009/07/23/simple-swipe-detection-in-the-iphone-sdk

#import "SwipeView.h"

@implementation SwipeView

@synthesize swipeDelegate;

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  CGPoint pt;
  NSSet *allTouches = [event allTouches];
  if ([allTouches count] == 1) {
    UITouch *touch = [[allTouches allObjects] objectAtIndex:0];
    if ([touch tapCount] == 1) {
      pt = [touch locationInView:self];
      touchBeganX = pt.x;
      touchBeganY = pt.y;
    }
  }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
  CGPoint pt;
  NSSet *allTouches = [event allTouches];
  if ([allTouches count] == 1) {
    UITouch *touch = [[allTouches allObjects] objectAtIndex:0];
    if ([touch tapCount] == 1) {
      pt = [touch locationInView:self];
      touchMovedX = pt.x;
      touchMovedY = pt.y;
    }
  }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
  NSSet *allTouches = [event allTouches];
  if ([allTouches count] == 1) {
    int diffX = touchMovedX - touchBeganX;
    int diffY = touchMovedY - touchBeganY;
    if (diffY >= -20 && diffY <= 20) {
      if (diffX > 20) {
        NSLog(@"swipe right");
        if (swipeDelegate) [swipeDelegate viewDidSwipeRight:self];
      } else if (diffX < -20) {
        NSLog(@"swipe left");
        if (swipeDelegate) [swipeDelegate viewDidSwipeLeft:self];
      }
    }
  }
}

- (void)dealloc {
  if (swipeDelegate) [swipeDelegate release];
  [super dealloc];
}
@end