设置收集视图单元格的动态宽度时出现问题

Question

I am trying to dynamically set the width of collection view cell. Initially it's not rendering as expected. But when I tap on the cell, its getting adjusted as I want. Here's the code that I wrote:

Code

import UIKit

class ViewController: UIViewController,UICollectionViewDelegate,UICollectionViewDataSource {

    @IBOutlet weak var collView: UICollectionView!


    var tasksArray = ["To Do", "SHOPPING","WORK"]
    var selectedIndex = Int()

    override func viewDidLoad() {
        super.viewDidLoad()
        let layout = collView?.collectionViewLayout as! UICollectionViewFlowLayout
        layout.itemSize = UICollectionViewFlowLayout.automaticSize
        layout.estimatedItemSize = CGSize(width: 93, height: 40)
        // Do any additional setup after loading the view, typically from a nib.
    }
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return tasksArray.count
    }
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! CollectionViewCell
        cell.lblName.text = tasksArray[indexPath.row]
        if selectedIndex == indexPath.row
        {
            cell.backgroundColor = UIColor.lightGray
        }
        else
        {
            cell.backgroundColor = UIColor.white
        }
        cell.layer.borderWidth = 1
        cell.layer.cornerRadius = cell.frame.height / 2
        return cell
    }
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        selectedIndex = indexPath.row
        self.collView.reloadData()
    }
}

here i am attaching two image before tapping and after tapping so you can easily understood

[![Here is the image before i tap

on cell] 2 ] 2

so please tell me whats wrong in my code

Answer 1

I have found a small trick for swift 4.2

For dynamic width & fixed height:

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    let label = UILabel(frame: CGRect.zero)
    label.text = textArray[indexPath.item]
    label.sizeToFit()
    return CGSize(width: label.frame.width, height: 32)
}

Answer 2

Inside your CollectionViewCell override preferredLayoutAttributesFitting function This is where the cell has a chance to indicate its preferred attributes, including size, which we calculate using auto layout.

 override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
    setNeedsLayout()
    layoutIfNeeded()
    let size = contentView.systemLayoutSizeFitting(layoutAttributes.size)
    var frame = layoutAttributes.frame
    frame.size.width = ceil(size.width)
    layoutAttributes.frame = frame
    return layoutAttributes
}

Answer 3

It is obvious that you have to use sizeForItemAt flow layout delegate in order to pass the dynamic width. But the tricky part is to calculate the width of the cell based on the text. You can actually calculate the width of a text given that you have a font.

Let's introduce few extension which will help us along the way

StringExtensions.swift

extension String {

    public func width(withConstrainedHeight height: CGFloat, font: UIFont) -> CGFloat {
        let constraintRect = CGSize(width: .greatestFiniteMagnitude, height: height)
        let boundingBox = self.boundingRect(with: constraintRect,
                                        options: .usesLineFragmentOrigin,
                                        attributes: [.font: font], context: nil)

        return ceil(boundingBox.width)
    }
}

This method let us know the width of a string, if i provide it the height and the font. Then use it inside sizeForItem as follows

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    let height = 40
    let text = YOUR_TEXT
    let width = text.width(withConstrainedHeight: height, font: Font.regular.withSize(.extraSmall)) + EXTRA_SPACES_FOR_LEFT_RIGHT_PADDING
    return CGSize(width: width, height: height)
}