FlickGestureRecognizer.m

#import "FlickGestureRecognizer.h"
#import <UIKit/UIGestureRecognizerSubclass.h>

@implementation FlickGestureRecognizer

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    [super touchesBegan:touches withEvent:event];
    
    _direction = FlickGestureRecognizerDirectionNone;
    
    if (1 == [touches count]) {
        self.state = UIGestureRecognizerStateBegan;
        return;
    }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    [super touchesMoved:touches withEvent:event];
    
    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInView:self.view];
    
    if(CGRectContainsPoint(self.view.bounds, location)) {
        _direction = FlickGestureRecognizerDirectionNone;
    }
    else {
        CGFloat x = location.x - CGRectGetWidth(self.view.frame) / 2;
        CGFloat y = location.y - CGRectGetHeight(self.view.frame) / 2;
        CGFloat radians = atan2f(y, x);
        if (radians < 0) {
            radians = M_PI * 2 + radians;
        }
        CGFloat degree = radians * 180 / M_PI;
        _direction = [self directionFromDegree:degree];
    }
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
    _direction = FlickGestureRecognizerDirectionNone;
    self.state = UIGestureRecognizerStateCancelled;
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    self.state = UIGestureRecognizerStateRecognized;
}

- (void)reset {
    [super reset];
    _direction = FlickGestureRecognizerDirectionNone;
}

- (FlickGestureRecognizerDirection)directionFromDegree:(CGFloat)degree
{
    FlickGestureRecognizerDirection direction = FlickGestureRecognizerDirectionNone;
    CGFloat offsetDegree = fmod((degree + 45.0f), 360.0f);
    
    if(90.0f > offsetDegree) {
        direction = FlickGestureRecognizerDirectionRight;
    }
    else if(180.0f > offsetDegree) {
        direction = FlickGestureRecognizerDirectionDown;
    }
    else if(270.0f > offsetDegree) {
        direction = FlickGestureRecognizerDirectionLeft;
    }
    else {
        direction = FlickGestureRecognizerDirectionUp;
    }
    
    return direction;
}
@end