Programming a variable speed slider for iPhone

Question

Hi, I have a slider with values from 0 to 100. I can easily stop at any number in the simulator but on my device the slider becomes a little jumpy and might move one or two ticks when you release your finger. I would like to have my slider act like the multispeed scrubber in the iPod, but I can't find a "prepackaged version" for the UISlider. I can't seem to capture the y coordinates of my touch once I have already grabbed the thumb of the slider. Or maybe it is a sensitivity issue. Any help would be much appreciated. Thanks

Answer 1

I'd write my own UISlider subclass and implement all the touch handling myself (i.e. in hitTest:withEvent:, return [self pointInside:point withEvent:event] ? self : nil;, using UISlider just to do the rendering (you can get the relevant min/max rects by calling thumbRectForValue: or whatever it's called).

I'm not sure what you mean by "I can't seem to capture the y coordinates of my touch", but it's not (easily) possible to access a touch event once a subview has "captured" it. One hack is to handle all touches yourself but then forward touchesBegan/Moved/Ended/Cancelled.

Answer 2

If I get your meaning it seems like you want the thumb to move at variable speed with the relative y position of the touch. I haven't used the scrubber control.

The UISlider control inherits from UIResponder so you can subclass it and add your own

– touchesBegan:withEvent:
– touchesMoved:withEvent:
– touchesEnded:withEvent:

touchesMoved will be of special interest since it will give you the y coordinate. Don't forget to call super and pass the events up the responder chain.

If you still get no events - maybe the thumb is in front and is intercepting them. Place a regular transparent UIView subclass over the slider, intercept touches and get coordinates there and again pass events up the chain.

I used this code once:

int progressAsInt = ((int)((completionSlider.value + 2.5f) / 5.0f) * 5);
 [sender setValue:progressAsInt animated:YES];

in the slider's action function to make a UISlider set its thumb to discrete values only, like a volume control with detents. You could use different values decided by the y position of the touches you have detected to vary the granularity you allow, or to influence the amount of movement represented by actual touch events.