UIPickerView: Get row value while spinning?

Question

I'd like to get the row value in real-time as the iPhone user spins a wheel in a UIPickerView (not just when the wheel settles onto a particular row). I looked into subclassing UIPickerView then overriding the mouseDown method, but I couldn't get this to work. Any suggestions would be very much appreciated.

Answer 1

Perhaps try implementing the delegate method:

- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view

You could treat it as a passthrough (just passing back the reusingView parameter) but each time it was called you would know that view was coming on the screen as the user scrolled - then you could calculate how many views offset from this one the center view was.

Answer 2

The UIPickerView dimensions are fairly consistent. Instead of subclassing it, perhaps you could overlay a UIView of your own on top of the picker view, from which you can track and measure dragging motions, before passing those touches down to the picker view.

Answer 3

You can find UIScrollView in UIPickerView hierarchy by the following method:

func findScrollView(view:UIView) -> UIScrollView? {
    if view is UIScrollView {
        return view as? UIScrollView
    }
    for subview in view.subviews {
        if subview is UIView {
            let result = findScrollView(subview as UIView)
            if result != nil {
                return result
            }
        }
    }
    return nil
}

Implement and setup UIScrollViewDelegate:

let scrollView = findScrollView(pickerView)
if scrollView != nil {
    scrollView!.delegate = self
}

And detect current selected item:

func scrollViewDidScroll(scrollView: UIScrollView) {
    let offset = scrollView.contentOffset.y
    let index = Int(offset/itemHeight)
    if index >= 0 && index < items.count {
        let item = items[index]
        // do something with item
    }
}