UICollectionView在reloadData上崩溃

Question

UICollectionview is loaded with simple cells and there is a simple int variable for calculating the number of items in the section.

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return viewCount
}

When the value of viewCount (initially at 45) is changed to a lower number (say 12) the app crashes.

This is error message to update the item count:

 *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'UICollectionView received layout attributes for a cell with an index path that does not exist: <NSIndexPath: 0x17402fbe0> {length = 2, path = 0 - 12}'

I tried reloading data and invalidating the cache as well as said here . This didn't help. I also tried reloading the indexSet before invalidating the cache. That didn't help either.

    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        if textField == countTextField {
            viewCount = Int(textField.text!)!
            textField.resignFirstResponder()
            let indexSet = IndexSet(integer: 0)

//            collectionView.reloadSections(indexSet)
            collectionView.reloadData()
            collectionView.collectionViewLayout.invalidateLayout()
        }

        return true
    }

I use 2 custom UICollectinViewLayout and I also set shouldInvalidateLayout to be true. Any help?

Update

func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "DemoCell", for: indexPath) as! DemoCollectionViewCell
        cell.indexLabel.text = "\(indexPath.item + 1)"

        return cell
    }

    @IBAction func showLayout1(_ sender: Any) {
        currentLayout = DemoACollectionViewLayout()
        animateLayout()
    }

    @IBAction func showLayout2(_ sender: Any) {
        currentLayout = DemoBCollectionViewLayout()
        animateLayout()
    }

    func animateLayout() {
        UIView.animate(withDuration: 0.3) { [weak self] value in
            guard let `self` = self else { return }
            self.collectionView.collectionViewLayout.invalidateLayout()
            self.collectionView.collectionViewLayout = self.currentLayout!
        }
    }

Here is the sample project.

Update : I have updated to use an dataObject to reload the UICollectionView but the cache in UICollectionViewLayout is not being cleared when I invalidate.

Answer 1

The cache must be cleared when the number of items for the collectionView has changed.

guard let views = collectionView?.numberOfItems(inSection: 0)
            else {
    cache.removeAll()
    return
}

if views != cache.count {
    cache.removeAll()
}

if cache.isEmpty { 
   //Layout attributes
}