UIPickerView, detect "rolling wheel" start and stop?

Question

I just discovered that if I do the following:

1. Click the button that animates a UIPickerView into my view
2. Quickly start the wheel rolling towards, then past, the last item
3. Dismiss the view with a button

Then it has not yet selected the last item yet.

I tried this by simply outputting to the console whenever the didSelectRow method was fired, and it fires when the wheel stabilizes on the last item.

Can I detect that the wheel is still rolling, so that I can delay checking it for a selected value until it stabilizes?

If it matters, I'm programming in MonoTouch, but I can read Objective-C code well enough to reimplement it, if you have a code example that is.

Answer 1

As animation keys don't work, I wrote this simple function that works for detecting if a UIPickerView is currently moving.

-(bool) anySubViewScrolling:(UIView*)view
{
    if( [ view isKindOfClass:[ UIScrollView class ] ] )
    {
        UIScrollView* scroll_view = (UIScrollView*) view;
        if( scroll_view.dragging || scroll_view.decelerating )
        {
            return true;
        }
    }

    for( UIView *sub_view in [ view subviews ] )
    {
        if( [ self anySubViewScrolling:sub_view ] )
        {
            return true;
        }
    }

    return false;
}

It ends up returning true five levels deep.

Answer 2

Swift 4 (updated) version with extension of @DrainBoy answers

extension UIView  {
 func isScrolling () -> Bool {

    if let scrollView = self as? UIScrollView {
        if  (scrollView.isDragging || scrollView.isDecelerating) {
            return true
        }
    }

    for subview in self.subviews {
        if ( subview.isScrolling() ) {
            return true
        }
    }
    return false
 }
}

Answer 3

Since animationKeys seems to not work anymore, I have another solution. If you check the subviews of UIPickerView, you'll see that there is a UIPickerTableView for each component.

This UIPickerTableView is indeed a subclass of UITableView and of course of UIScrollView. Therefore, you can check its contentOffset value to detect a difference.

Besides, its scrollViewDelegate is nil by default, so I assume you can safely set an object of yours to detect scrollViewWillBeginDragging, scrollViewDidEndDecelerating, etc.

By keeping a reference to each UIPickerTableView, you should be able to implement an efficient isWheelRolling method.

Answer 4

Expanded @iluvatar_GR answer

extension UIView { 
func isScrolling () -> Bool {

    if let scrollView = self as? UIScrollView {
        if (scrollView.isDragging || scrollView.isDecelerating) {
            return true
        }
    }

    for subview in self.subviews {
        if ( subview.isScrolling() ) {
            return true
        }
    }
    return false
}
func waitTillDoneScrolling (completion: @escaping () -> Void) {
    var isMoving = true
    DispatchQueue.global(qos: .background).async {
    while isMoving == true {
        isMoving = self.isScrolling()
    }
        DispatchQueue.main.async {
            completion()}

    }
}
}

Answer 5

Expanded @iluvatar_GR, @Robert_at_Nextgensystems answer

Used Gesture, UIScrollView isDragging or isDecelerating.

// Call it every time when Guesture action.
@objc func respondToSwipeGesture(gesture: UIGestureRecognizer) {
    // Changes the button name to scrolling at the start of scrolling.
    DispatchQueue.main.async {
       self._button.setTitle("Scrolling...", for: .normal)
       self._button.isEnabled = false
       self._button.backgroundColor = Utils.hexStringToUIColor(hex: "FF8FAE")
    }

    // Indication according to scrolling status
    _datePicker.waitTillDoneScrolling(completion: {
        print("completion")
        DispatchQueue.main.async {
           self._button.setTitle("Completion", for: .normal)
           self._button.isEnabled = true
           self._button.backgroundColor = Utils.hexStringToUIColor(hex: "7CB0FF")
        }
    })
}

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• Reference : How to recognize swipe in all 4 directions