嵌套的UICollectionView和Responder链

Question

I have two UICollectionVews

• One of them (The parent one) is a full-screen-cell paginated collection view.

• The other one (The child one) is a filter inside the "page" Both have the same scroll direction

My problem is that when I'm scrolling the child one, and it reaches the end, the parent one starts moving. And I would like to avoid that. I tried many things

*ScrollView delegates *Touchesbegan

Any ideas? Thanks!

Answer 1

I think it's easy . To set the parent UICollectionView

collectionView.scrollEnabled = NO;

Or it sounds unreasonable . If the parent UICollectionView could scroll, how could you archive your goal? Because UICollectionView is consisted of the cells (The child one). The cell will affect the parent UICollectionView inevitably.

Maybe The child one is located in part of the cell , you could use the

UIScrollViewDelegate 's method: scrollViewDidScroll , to set the parent collectionView's scrollEnabled property.

Answer 2

I think you prefer this answer. As we know a pan gesture recognizer is built in UIScrollView. We could add an other coordinated pan gesture.

Because the apple says: 'UIScrollView's built-in pan gesture recognizer must have its scroll view as its delegate.'

        let pan = UIPanGestureRecognizer(target: self, action: #selector(ViewController.panGestureRecognizerAction(recognizer:)))
          pan.delegate = self
          mainScrollView.addGestureRecognizer(pan)

          func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, 
                                shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
                return true
            }
     // So we can get the argus of the pan gesture while not affecting the scroll 
     after the setting. 

            var mainScrollEnabled = false
            var subScrollEnabled = false
    // Then we define two BOOL values to identify the scroll of the collectionView    

        func scrollViewDidScroll(_ scrollView: UIScrollView) {
                if scrollView == mainScrollView {
                    if scrollView.contentOffset.y >= maxOffsetY {
                        scrollView.setContentOffset(CGPoint(x: 0, y: maxOffsetY), animated: false)
                        mainScrollView.isScrollEnabled = false
                        subScrollView.isScrollEnabled = true
                        subScrollEnabled = true
                         mainScrollEnabled = false
                    }
                }else {
                    if scrollView.contentOffset.y <= 0 {
                        scrollView.setContentOffset(CGPoint(x: 0, y: 0), animated: false)
                        subScrollView.isScrollEnabled = false
                        mainScrollView.isScrollEnabled = true
                        mainScrollEnabled = true
                        subScrollEnabled = false
                    }
                }
            }

// Then we handle the situation that the collectionView reaches the end , by the pan gesture's recognizer .    
            var currentPanY: CGFloat = 0

            func panGestureRecognizerAction(recognizer: UIPanGestureRecognizer) {
                    if recognizer.state != .changed{
                        currentPanY = 0
                        // clear the data of last time after finishing the scroll 
                        mainScrollEnabled = false
                        subScrollEnabled = false
                    }else {
                       let currentY = recognizer.translation(in: mainScrollView).y
                       // So the collectionView reaches the end.
                        if mainScrollEnabled || subScrollEnabled {
                            if currentPanY == 0 {
                                currentPanY = currentY  //get the y
                            }
                            let offsetY = currentPanY - currentY //get the offsetY

                            if mainScrollEnabled {
                               let supposeY = maxOffsetY + offsetY
                                if supposeY >= 0 {
                                    mainScrollView.contentOffset = CGPoint(x: 0, y: supposeY)
                                }else {
                                    mainScrollView.contentOffset = CGPoint.zero
                                }
                            }else {
                                subScrollView.contentOffset = CGPoint(x: 0, y: offsetY)
                            }
                        }
                    }
                }