Simultaneous gesture recognizers in Iphone SDK

I need to catch two different swipping gestures using UISwipeGestureRecognizer(for example, UISwipeGestureRecognizerDirectionRight and UISwipeGestureRecognizerDirectionLeft). When I add two different recognisers with addGestureRecognizer method, only last added recognizer works. I've read that I need to implement gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer: method of UIGestureRecognizerDelegate protocol, but nothing works.

Can anyone help with simple example of catching two or more same gestures? Thanks!

Solution 1:

It was really easy:

At first we should create class, that implements UIGestureRecognizerDelegate protocol:

@interface MyGestureDelegate : NSObject <UIGestureRecognizerDelegate>

@implementation MyGestureDelegate

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer{
    return YES;
}

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer{
    return YES;
}
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldReceiveTouch:(UITouch *)touch{
    return YES;
}

And use it like this:

    UISwipeGestureRecognizer *swipeGestureLeft = [[UISwipeGestureRecognizer alloc]
                                              initWithTarget:self action:@selector(handleSwipeGestureLeft:)];
    [self.view addGestureRecognizer:swipeGestureLeft];
    swipeGestureLeft.direction = UISwipeGestureRecognizerDirectionLeft;
    [swipeGestureLeft release];

    UISwipeGestureRecognizer *swipeGesture = [[UISwipeGestureRecognizer alloc]
                                          initWithTarget:self action:@selector(handleSwipeGesture:)];
    swipeGesture.direction = UISwipeGestureRecognizerDirectionRight;
    [self.view addGestureRecognizer:swipeGesture];

    MyGestureDelegate *deleg = [[MyGestureDelegate alloc] init];

    [swipeGesture setDelegate:deleg];
    [swipeGesture release];

Solution 2:

The answer: "Um, a quick look at the documentation..." from Phoenix absolutely will not work!

He is setting a mask, then using the same variable to test as if the recognizer cleared it and set a single bit. It stores, as he correctly quoted from the documentation:

The permitted directions of the swipe

sender.direction

will simply return the mask you set initially and in his example, will never resolve to a single direction!

UISwipeGestureRecognizerDirectionRight == 1
UISwipeGestureRecognizerDirectionRight | UISwipeGestureRecognizerDirectionLeft == 3

Additionaly, for most cases you don't need to:

• setup a delegate
• permit simultaneous gesture recognition (unless you want simultaneous swipes; not likely)
• send the recognizer to the selector

The following works for me:

   UISwipeGestureRecognizer* swipe;

   swipe = [[[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipeL)] autorelease];
   swipe.direction = UISwipeGestureRecognizerDirectionLeft;
   [view addGestureRecognizer:swipe];

   swipe = [[[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipeR)] autorelease];
   swipe.direction = UISwipeGestureRecognizerDirectionRight; // default
   [view addGestureRecognizer:swipe];