Question

I’m posting this message because I’ve been reading the forum and I haven’t been able to find a similar problem. I need to be able to discriminate taps and double taps (this is a standard thing) BUT my problem is that for whatever reasons I have a Scroll View inside another ScrollView. So, I had to sub-class my ScrollView in order to get touchedBegin method called.

I have a class called PhotoViewController (a sub-class of BaseViewController) this class contains another class called CustomScrollView (a subclass of ScrollView). I needed to sub-class this CustomScrollView from ScrollView in order to override the touchesBegin method, and to be able to capture the touches made by the user.

I tried calling the touchesBegin method from CustomScrollView using something like return [super touchesBegan:touches withEvent:event] inside the touchesBegin method, but when the touchesBegin method inside PhotoViewController gets called it’s parameters are empty (and I can’t discriminate if the user made a single or double tap, which is exactly what I need)

I have a class, called PhotoViewController:

@class PhotoViewController
@interface PhotoViewController : BaseViewController  <UIScrollViewDelegate> {

    CustomScrollView*           myScrollView;

}

@implementation PhotoViewController

...

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];

    NSUInteger tapCount = [touch tapCount];

    switch (tapCount) {
        case 1:

            [self performSelector:@selector(singleTapMethod) withObject:nil afterDelay:.4];
            break;
        case 2:

            [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(singleTapMethod) object:nil];
            [self performSelector:@selector(doubleTapMethod) withObject:nil afterDelay:.4];
            break;
        default:
            break;
    }

}

the class CustomScrollView is (CustomScrollView.h):

@interface CustomScrollViewPhoto : UIScrollView {
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;

@end

and it’s implementation is this(CustomScrollView.m):

@implementation CustomScrollViewPhoto

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {    
    [self.superview touchesBegan:[NSSet set] withEvent:event];
    return [super touchesBegan:touches  withEvent:event];
}

Am I going in the wrong direction with what I want to do? Maybe, I should capture the taps/double taps inside the CustomScrollView class(this works fine!), and from there using a @selector or something call the appropiate methods in PhotoViewController?

Thanks for reading!

Answer 1

I think you’re going the wrong route (only slightly!). I do a very similar thing in a photo viewer and I capture the touches in the CustomScrollView. You shouldn’t need to do anything in PhotoViewController.

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    [super touchesEnded:touches withEvent:event];

    UITouch *touch = [touches anyObject];

    if(touch.tapCount == 2)
    {
        if (self.zoomScale == self.minimumZoomScale)
        {
            //Zoom where the user has clicked from
            CGPoint pos = [touch locationInView:self];
            [self zoomToRect:CGRectMake((pos.x - 5.0)/self.zoomScale, (pos.y-5.0)/self.zoomScale, 10.0, 10.0) animated:YES];
        }
        else
        {
            //Zoom back out to full size
            [self setZoomScale:self.minimumZoomScale animated:YES];
        }
    }
}