Help understanding UIGestureRecognizer

[TronPlayer]

Could someone please tell me why there are 4 events called sequentially in UIGestureRecognizer? I was initially thinking that the events being passed were UITouchesBegan, UITouchesEnded, etc but now I am unsure. I need to call a function in UIGestureRecognizer a single time when the user initially touches an object. Could someone post a sample solution?


- (BOOL)gestureRecognizerUIGestureRecognizer *)gestureRecognizer shouldReceiveTouchUITouch *)touch {
NSLog(@"Triggered");
}

[Domele]

To receive a message that something has been touched, you need to add a target and a selector to the UIGestureRecognizer. The method you posted is whether the recognizer should message the target with the specified method.

[TronPlayer]

The app needs to detect rapid, consecutive touches on an UIImageView object with two fingers alternating back and forth. Using a single finger the events come trough TouchesBegan just fine. However, with two fingers using the same rapid back and forth motion the events discontinue. I am assuming that at this point the system is detecting a gesture instead. Do you have any suggestions on how to remedy this?

[Domele]

I would see maybe if it detecting a double tap. Set up a gesture recognizer for that and if it turns out that it is, just have 2 gesture recognizers that call the same method.

[TronPlayer]

It's not detecting a doubletap but rather once two fingers happen to touch the UIImageView at the same time the events become sporatic. Is there anyway to turn off multitouch or equivilant to prevent this?

[BrianSlick]

I haven't gone too complicated with gesture recognizers, but you should be able to look at the touches and the state to see what is happening. Ex:

- (void)handleTapGesture:(UIGestureRecognizer *)gestureRecognizer
{
   UIGestureRecognizerState state = [gestureRecognizer state];
...

I'm going to make a guess that each time you change fingers, you're canceling the previous touch. Not sure. But taking a look at this state, and using some of the other UIGestureRecognizer instance methods will help you to figure out what is happening.

I'm also going to make a guess that you'll need to add 2 subviews to your image view, so that each finger is touching one view and each view has its own recognizer, and then handling things that way. Not sure.

[baja_yu]

If you just need notifications of when a finger first touches the screen, you could implement the old

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