CollectionView Dynamic cell height swift

问题:

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
    }

回答1:

You can dynamically set the frame of the cell in the cellForItemAtIndexPath function, so you can customize the height based on a label if you disregard the sizeForItemAtIndexPath function. With customizing the size, you'll probably have to look into collection view layout flow, but hopefully this points you in the right direction. It may look something like this:

class CollectionViewController: UICollectionViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    var array = ["a","as","asd","asdf","asdfg","asdfgh","asdfghjk","asdfghjklas","asdfghjkl","asdghjklkjhgfdsa"]
    var heights = [10.0,20.0,30.0,40.0,50.0,60.0,70.0,80.0,90.0,100.0,110.0] as [CGFloat]

    override func viewDidLoad() {
        super.viewDidLoad()
    }


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

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

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

            let cell = collectionView.dequeueReusableCellWithReuseIdentifier("CellID", forIndexPath: indexPath) as Cell
            cell.textLabel.text = array[indexPath.row]
            cell.textLabel.sizeToFit()

            // Customize cell height
            cell.frame = CGRectMake(cell.frame.origin.x, cell.frame.origin.y, cell.frame.size.width, heights[indexPath.row])
            return cell
    }

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
        return CGSizeMake(64, 64)
    }
}

which gives dynamic heights like so

回答2:

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)
}

回答3:

In Swift 3, use the below method:

private func updateCollectionViewLayout(with size: CGSize) {
    var margin : CGFloat = 0;
    if isIPad {
        margin = 10
    }
    else{
        margin = 6
        /* if UIDevice.current.type == .iPhone6plus || UIDevice.current.type == .iPhone6Splus || UIDevice.current.type == .simulator{
         margin = 10

         }
         */
    }
    if let layout = menuCollectionView.collectionViewLayout as? UICollectionViewFlowLayout {
        layout.itemSize = CGSize(width:(self.view.frame.width/2)-margin, height:((self.view.frame.height-64)/4)-3)
        layout.invalidateLayout()
    }
}