layout - CollectionView 动态单元格高度 swift

Question

我正在尝试创建一个 Collection View ，其中的单元格显示可变长度的字符串。

我正在使用这个函数来设置单元格布局:

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

我想做的是根据我的 cell.labelString.utf16Count 长度操纵 cellSize.height。基本逻辑是 sa that

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

但是，我无法设法检索始终返回 nil 的单元格标签字符串长度。 (我认为它还没有加载...

为了更好的理解，这里是完整的代码:

// 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

虽然上面的答案可能会解决您的问题，但它建立了一种分配每个单元格高度的相当粗略的方法。您被迫根据某些估计对每个单元格高度进行硬编码。处理此问题的更好方法是在 collectionview 的 sizeForItemAtIndexPath 委托(delegate)方法中设置每个单元格的高度。

我将在下面引导您完成有关如何执行此操作的步骤。

第 1 步:让您的类扩展 UICollectionViewDelegateFlowLayout

第 2 步:创建一个函数来估计文本的大小:此方法将返回适合您的字符串的高度值!

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)
}

第 3 步:使用或覆盖下面的委托(delegate)方法:

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)
}