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I'm attempting to convert my web app into a form usable by mobile devices. I'm attempting to build in support for touch gestures like horizontal scrolling. I'm finding some strange behavior in my app.

I start a gesture with a touchstart event, and then scroll on touchmove. However, my application sees a 500-700 ms delay between receiving these two events. As far as I can tell, my app is doing no other work between these two events.

Other aspects: The code is written in jquery, using 

  $(element).bind(touchmove, function(ev) {return myobject.DoTouch(ev) }

were the DoTouch command simply checks the ev.type, records the touch position, and returns false.

Any ideas what I should look for to try to solve this? The lag between touching and getting a response from the app is very annoying.

Nathaniel Tagg
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1 Answers1

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Yes. It turns out, this is how iOS works. I was pulling my own hair out for some time. Read more here: http://developer.apple.com/library/ios/#DOCUMENTATION/AppleApplications/Reference/SafariWebContent/HandlingEvents/HandlingEvents.html. Essentially, if iOS thinks it can handle this as an internal PAN gesture, it does and doesn't even bother sending a touchmove event at all.

In my project, I found that if the viewer makes the touchmove gesture very deliberately and pauses a bit longer before lifting the finger at the end of the move, then the touchmove event is, in fact, sent as one might expect. So, the documented behaviour may be a little iffy versus reality, which only added to confusion and my debugging efforts.

Anyway, if iOS handles the event internally as a PAN gesture, it will send a scroll event before the touchend. In my project I was able to use this to set the flag I was using to distinguish dragging gestures (which was normally sent in my touchmove handler) and ignore any behaviour in stand-alone touchend handlers that were not related to the handling of my own scroll-handling.

I hope this helps you (and others) as well!

mkoistinen
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