layout - CollectionView Dynamic cell height swift

Question

Im trying to create a collection view with cells displaying string with variable length.

Im using this function to set cell layout:

 func collectionView(collectionView : UICollectionView,layout collectionViewLayout:UICollectionViewLayout,sizeForItemAtIndexPath indexPath:NSIndexPath) -> CGSize
    {
        var cellSize:CGSize = CGSizeMake(self.whyCollectionView.frame.width, 86)
        return cellSize
    }

what I would like to do is manipulate cellSize.height based on my cell.labelString.utf16Count length. the basic logic would be to sa that

if((cell.labelString.text) > 70){
   cellSize.height = x
}
else{
   cellSize.height = y
}

However, I can't manage to retrieve my cell label string length which always return nil. (I think it's not loaded yet...

for better understanding, here is the full code:

// WhyCell section
    var whyData:NSMutableArray! = NSMutableArray()
    var textLength:Int!
    @IBOutlet weak var whyCollectionView: UICollectionView!

//Loading data
    @IBAction func loadData() {
        whyData.removeAllObjects()

        var findWhyData:PFQuery = PFQuery(className: "PlacesWhy")
        findWhyData.whereKey("placeName", equalTo: placeName)

        findWhyData.findObjectsInBackgroundWithBlock({
            (objects:[AnyObject]!,error:NSError!)->Void in

            if (error == nil) {
                for object in objects {
                    self.whyData.addObject(object)
                }

                let array:NSArray = self.whyData.reverseObjectEnumerator().allObjects
                self.whyData = array.mutableCopy() as NSMutableArray

                self.whyCollectionView.reloadData()
                println("loadData completed. datacount is (self.whyData.count)")
            }
        })
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
        self.loadData()


    }

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

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return whyData.count
    }

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell:whyCollectionViewCell = whyCollectionView.dequeueReusableCellWithReuseIdentifier("whyCell", forIndexPath: indexPath) as whyCollectionViewCell

        // Loading content from NSMutableArray to cell
        let therew:PFObject = self.whyData.objectAtIndex(indexPath.row) as PFObject
        cell.userWhy.text = therew.objectForKey("why") as String!
        textLength = (therew.objectForKey("why") as String!).utf16Count
        self.whyCollectionView.layoutSubviews()

        // Displaying user information
        var whatUser:PFQuery = PFUser.query()
        whatUser.whereKey("objectId", equalTo: therew.objectForKey("reasonGivenBy").objectId)

        whatUser.findObjectsInBackgroundWithBlock({
            (objects: [AnyObject]!, error: NSError!)->Void in

            if !(error != nil) {
                if let user:PFUser = (objects as NSArray).lastObject as? PFUser {
                    cell.userName.text = user.username
                    // TODO Display avatar
                }

            }
        })

        return cell
    }

    func collectionView(collectionView : UICollectionView,layout collectionViewLayout:UICollectionViewLayout,sizeForItemAtIndexPath indexPath:NSIndexPath) -> CGSize
    {
        var cellSize:CGSize = CGSizeMake(self.whyCollectionView.frame.width, 86)
        return cellSize
    }

Answer 1

While the answer above may solve your problem, it establishes a pretty crude way of assigning each cells height. You are being forced to hard code each cell height based on some estimation. A better way of handling this issue is by setting the height of each cell in the collectionview's sizeForItemAtIndexPath delegate method.

I will walk you through the steps on how to do this below.

Step 1: Make your class extend UICollectionViewDelegateFlowLayout

Step 2: Create a function to estimate the size of your text: This method will return a height value that will fit your string!

private func estimateFrameForText(text: String) -> CGRect {
    //we make the height arbitrarily large so we don't undershoot height in calculation
    let height: CGFloat = <arbitrarilyLargeValue>

    let size = CGSize(width: yourDesiredWidth, height: height)
    let options = NSStringDrawingOptions.UsesFontLeading.union(.UsesLineFragmentOrigin)
    let attributes = [NSFontAttributeName: UIFont.systemFontOfSize(18, weight: UIFontWeightLight)]

    return NSString(string: text).boundingRectWithSize(size, options: options, attributes: attributes, context: nil)
}

Step 3: Use or override delegate method below:

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
    var height: CGFloat = <someArbitraryValue>

   //we are just measuring height so we add a padding constant to give the label some room to breathe! 
    var padding: CGFloat = <someArbitraryPaddingValue>

    //estimate each cell's height
    if let text = array?[indexPath.item].text {
         height = estimateFrameForText(text).height + padding
    }
    return CGSize(width: yourDesiredWidth, height: height)
}