Observing pinch multi-touch gestures in a UITableView

Question

I am looking to implement a pinch in/out on top of a UITableView, I have looked at several methods including this one:

Similar question

But while I can create a UIViewTouch object and overlay it onto my UITableView, scroll events are not being relayed to my UITableView, I can still select cells, and they respond properly by triggering a transition to a new ViewController object. But I can not scroll the UITableView despite passing the touchesBegan, touchesMoved, and touchesEnded events.

Answer 1

This seems to be a classic problem. In my case I wanted to intercept some events over a UIWebView which can't be subclassed, etc etc.

I've found that the best way to do it is to intercept the events using the UIWindow:

EventInterceptWindow.h

@protocol EventInterceptWindowDelegate
- (BOOL)interceptEvent:(UIEvent *)event; // return YES if event handled
@end


@interface EventInterceptWindow : UIWindow {
    // It would appear that using the variable name 'delegate' in any UI Kit
    // subclass is a really bad idea because it can occlude the same name in a
    // superclass and silently break things like autorotation.
    id <EventInterceptWindowDelegate> eventInterceptDelegate;
}

@property(nonatomic, assign)
    id <EventInterceptWindowDelegate> eventInterceptDelegate;

@end

EventInterceptWindow.m:

#import "EventInterceptWindow.h"

@implementation EventInterceptWindow

@synthesize eventInterceptDelegate;

- (void)sendEvent:(UIEvent *)event {
    if ([eventInterceptDelegate interceptEvent:event] == NO)
        [super sendEvent:event];
}

@end

Create that class, change the class of your UIWindow in your MainWindow.xib to EventInterceptWindow, then somewhere set the eventInterceptDelegate to a view controller that you want to intercept events. Example that intercepts a double-tap:

- (BOOL)interceptEvent:(UIEvent *)event {
    NSSet *touches = [event allTouches];
    UITouch *oneTouch = [touches anyObject];
    UIView *touchView = [oneTouch view];
    //  NSLog(@"tap count = %d", [oneTouch tapCount]);
    // check for taps on the web view which really end up being dispatched to
    // a scroll view
    if (touchView && [touchView isDescendantOfView:webView]
            && touches && oneTouch.phase == UITouchPhaseBegan) {
        if ([oneTouch tapCount] == 2) {
            [self toggleScreenDecorations];
            return YES;
        }
    }   
    return NO;
}

Related info here: http://iphoneincubator.com/blog/windows-views/360idev-iphone-developers-conference-presentation