Question

I implemented gesture recognizer in UIMapView just as described in the accepted answer to this question: How to intercept touches events on a MKMapView or UIWebView objects?

Single touches are recognized correctly. However, when I changed the superclass of my class from UIGestureRecognizer to UIPinchGestureRecognizer in order to recognize map scaling, everything stopped working.
Now TouchesEnded event occurs only when the user double tap the annotation on map (don’t know, why!) and doesn’t occur when the user pinches the map (zoom in or out doesn’t matter).

PS I’m using iOS SDK 4.3 and testing my app in simulator if that matters.

The code of mapViewController.m – viewDidLoad method:

 - (void)viewDidLoad
 {
     [super viewDidLoad];
     MapGestureRecognizer *changeMapPositionRecognizer = [[MapGestureRecognizer alloc] init];
     changeMapPositionRecognizer.touchesEndedCallback = ^(NSSet * touches, UIEvent * event) 
     {
        ...
     };
     [self.mapView addGestureRecognizer:changeMapPositionRecognizer];
     [changeMapPositionRecognizer release];
}

The code of MapGestureRecognizer.h:

#import <UIKit/UIKit.h>
typedef void (^TouchesEventBlock) (NSSet * touches, UIEvent * event);
@interface MapGestureRecognizer : UIPinchGestureRecognizer    
@property(nonatomic, copy) TouchesEventBlock touchesEndedCallback;
@end

The code of MapGestureRecognizer.m:

#import "MapGestureRecognizer.h"

@implementation MapGestureRecognizer
@synthesize touchesEndedCallback = _touchesEndedCallback;

- (id)init
{
    self = [super init];
    if (self) {
        self.cancelsTouchesInView = NO;
}

    return self;
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    if (self.touchesEndedCallback)
    {
        self.touchesEndedCallback(touches, event);
        NSLog(@"Touches ended, callback done");
    }
    else
    {
        NSLog(@"Touches ended, callback skipped");
    }
}

- (void) dealloc
{
    [super dealloc];
}

@end

What should I correct in to make pinch gesture to be recognized?

Answer 1

I’m not sure why you need to subclass UIPinchGestureRecognizer instead of using it directly as-is.

Also not sure why you need the gesture recognizer to detect map scaling which you could do by using the delegate methods regionWillChangeAnimated and regionDidChangeAnimated and comparing the span before and after. Unless you are trying to detect the scaling as it is happening (and not wanting to wait until user finishes the gesture)

The gesture recognizer may not be getting called because the map view’s own pinch gesture recognizer is getting called instead.

To have your recognizer called as well as the map view’s, implement the UIGestureRecognizer delegate method shouldRecognizeSimultaneouslyWithGestureRecognizer and return YES:

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

Make sure the gesture recognizer’s delegate property is set or that method won’t get called either.