Changes in UISlider / touch events in iOS 7

Question

I ran into an iOS 7 issue that I think is related to how events are handled. I have a slider that, when changing its value, performs some image processing, which takes about 100 ms. In iOS 6, I could see the image change when dragging the slider. After upgrading to iOS 7, it seems that the view does not redraw between calls to the changed values. While dragging the slider, I see that image processing starts and ends many times, but the whole view is not updated (including the large slider) until I stop sliding. The same thing happens when I add a gesture handler to a view that does the same. Has anyone encountered a similar problem?

Thanks.

Answer 1

Make sure you are not doing this processing in the main thread. I recommend using GCD to send processing to a separate queue - it takes very little code and uses a well-established template that is easy to understand.