Question

I’m trying to detect when a user touches down and up in a view. The view contains some buttons and other UIKit controls. I would like to detect these touch events but not consume them.

I’ve tried two approaches, but neither has been sufficient:

First I added a transparent overlay overriding -touchesBegan:withEvent: and -touchesEnded:withEvent: and forward the event to the next responder with

[self.nextResponder touchesBegan:touches withEvent:event]

However, it seems that UIKit objects ignore all forwarded events.

Next, I tried overriding -pointInside:withEvent: and -hitTest:withEvent: . This worked great to detect touch down events, but pointInside:: and hitTest:: are not called on touch up (i.e. [[[event allTouches] anyObject] phase] is never equal to UITouchPhaseEnded ).

What’s the best way to detect both touch down and touch up events without disturbing interaction with the underlying UIControls?

Answer 1

according to the Event Handling Guide for iOS
you have 3 options:

1) subclassing UIWindow to override sendEvent:

2) using an overlay view

3) designing so that you don’t have to do that… so really more like 2 options.

Here is a simplification of apples example, using UIWindow subclass;

1) change the class of your window in the NIB to your subclass of UIWindow.
2) put this method in the .m file.

- (void)sendEvent:(UIEvent *)event
{
    NSSet * allTouches = [event allTouches];

    NSMutableSet *began = nil;
    NSMutableSet *moved = nil;
    NSMutableSet *ended = nil;
    NSMutableSet *cancelled = nil;

    // sort the touches by phase so we can handle them similarly to normal event dispatch
    for(UITouch *touch in allTouches) {
        switch ([touch phase]) {
            case UITouchPhaseBegan:
                if (!began) began = [NSMutableSet set];
                [began addObject:touch];
                break;
            case UITouchPhaseMoved:
                if (!moved) moved = [NSMutableSet set];
                [moved addObject:touch];
                break;
            case UITouchPhaseEnded:
                if (!ended) ended = [NSMutableSet set];
                [ended addObject:touch];
                break;
            case UITouchPhaseCancelled:
                if (!cancelled) cancelled = [NSMutableSet set];
                [cancelled addObject:touch];
                break;
            default:
                break;
        }

        // call our methods to handle the touches
        if (began)
        {
            NSLog(@"the following touches began: %@", began);
        };
        if (moved)
        {
            NSLog(@"the following touches were moved: %@", moved);
        };
        if (ended)
        {
             NSLog(@"the following touches were ended: %@", ended);
        };
        if (cancelled) 
        {
             NSLog(@"the following touches were cancelled: %@", cancelled);
        };
    }
    [super sendEvent:event];
}

It has way too much output, but you will get the idea… and can make your logic fit where you want it to.