Martin Martin - 3 months ago 11
Objective-C Question

How to intercept touches events on a MKMapView or UIWebView objects?

I'm not sure what i'm doing wrong but I try to catch touches on a MKMapView object. I subclassed it by creating the following class :

#import <UIKit/UIKit.h>
#import <MapKit/MapKit.h>

@interface MapViewWithTouches : MKMapView {

}

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

@end


And the implementation :

#import "MapViewWithTouches.h"
@implementation MapViewWithTouches

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

NSLog(@"hello");
//[super touchesBegan:touches withEvent:event];

}
@end


But it looks like when I use this class, I see nothing on the Console :

MapViewWithTouches *mapView = [[MapViewWithTouches alloc] initWithFrame:self.view.frame];
[self.view insertSubview:mapView atIndex:0];


Any idea what I'm doing wrong?

Answer

The best way I have found to achieve this is with a Gesture Recognizer. Other ways turn out to involve a lot of hackish programming that imperfectly duplicates Apple's code, especially in the case of multitouch.

Here's what I do: Implement a gesture recognizer that cannot be prevented and that cannot prevent other gesture recognizers. Add it to the map view, and then use the gestureRecognizer's touchesBegan, touchesMoved, etc. to your fancy.

How to detect any tap inside an MKMapView (sans tricks)

WildcardGestureRecognizer * tapInterceptor = [[WildcardGestureRecognizer alloc] init];
tapInterceptor.touchesBeganCallback = ^(NSSet * touches, UIEvent * event) {
        self.lockedOnUserLocation = NO;
};
[mapView addGestureRecognizer:tapInterceptor];

WildcardGestureRecognizer.h

//
//  WildcardGestureRecognizer.h
//  Copyright 2010 Floatopian LLC. All rights reserved.
//

#import <Foundation/Foundation.h>

typedef void (^TouchesEventBlock)(NSSet * touches, UIEvent * event);

@interface WildcardGestureRecognizer : UIGestureRecognizer {
    TouchesEventBlock touchesBeganCallback;
}
@property(copy) TouchesEventBlock touchesBeganCallback;


@end

WildcardGestureRecognizer.m

//
//  WildcardGestureRecognizer.m
//  Created by Raymond Daly on 10/31/10.
//  Copyright 2010 Floatopian LLC. All rights reserved.
//

#import "WildcardGestureRecognizer.h"


@implementation WildcardGestureRecognizer
@synthesize touchesBeganCallback;

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

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    if (touchesBeganCallback)
        touchesBeganCallback(touches, event);
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
}

- (void)reset
{
}

- (void)ignoreTouch:(UITouch *)touch forEvent:(UIEvent *)event
{
}

- (BOOL)canBePreventedByGestureRecognizer:(UIGestureRecognizer *)preventingGestureRecognizer
{
    return NO;
}

- (BOOL)canPreventGestureRecognizer:(UIGestureRecognizer *)preventedGestureRecognizer
{
    return NO;
}

@end