CODEWITHSUNDEEP
iosswiftuicollectionview
Anton
Anton

Reputation: 947

FlowLayout of UICollectionView and reloadData()

My app crashes when I use FlowLayout object in the code and call reloadData() on CollectionView object. I do not have such exception when I use standard FlowLayout (settings from XCode).

This is how I use FlowLayout to calculate section's inset depending on device width.

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    let layout = UICollectionViewFlowLayout()
    layout.itemSize = CGSize(width: itemWidth, height: itemWidth)
    layout.minimumInteritemSpacing = minItemSpacing
    layout.minimumLineSpacing = minItemSpacing

    layout.headerReferenceSize = CGSize(width: 0, height: headerHeight)

    let containerWidth = collectionView.bounds.width
    if (containerWidth < 350) {
        inset = 2
    }
    else if (containerWidth >= 350 && containerWidth < 400) {
        inset = 10
    }
    else {
        inset = 14
    }
    layout.sectionInset = UIEdgeInsets(top: minItemSpacing, left: inset, bottom: minItemSpacing, right: inset)

    collectionView.collectionViewLayout = layout
}

with such code app starts normally, but when I go from another view controller to main where CollectionView is used and collectionView.reloadData() is called

@IBAction func saveMyObjects(segue:UIStoryboardSegue) {
    if let myObjectsViewController = segue.sourceViewController as? MyObjectsViewController {
        MyObjects.Objects.removeAll()
        MyObjects.Objects.appendContentsOf(myObjectsViewController.MyObjects)
        collectionView.reloadData()
    }
}

app crashes with the following exception.

* Terminating app due to uncaught exception 'NSRangeException', reason: '* -[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array' libc++abi.dylib: terminating with uncaught exception of type NSException

If I comment 

// collectionView.collectionViewLayout = layout

line to use values from XCode, app works without exception.

Additional code:

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

    let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! ObjectCollectionViewCell
    // Configure the cell
    cell.imageView.image = UIImage(named: Groups[indexPath.section].Objects[indexPath.row].Image)
    cell.label.text = Groups[indexPath.section].Objects[indexPath.row].Name
    if (Groups[indexPath.section].Objects[indexPath.row].Image != "") {
        cell.label.hidden = true
        cell.imageView.hidden = false
    }
    else {
        cell.imageView.hidden = true
        cell.label.hidden = false
    }
    return cell
}

Upvotes: 0

Views: 1391

Answers (1)

Reinier Melian
Reinier Melian

Reputation: 20804

after to review your code so many times, I think that your problem is that you should remove the code from viewDidLayoutSubviews() and implement the methods existing on UICollectionViewDelegateFlowLayout to do what you need,

optional public func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize

optional public func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAtIndex section: Int) -> CGFloat

optional public func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAtIndex section: Int) -> CGFloat

optional public func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize

optional public func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets

I think if you implement this methods and remove your code from viewDidLayoutSubviews() your code will work as you need, Is highly discouraged to do that with your approach ;), I hope this helps you

Upvotes: 0

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