How to set UICollectionViewCell Width and Height programmatically

Question

I am trying to implement a CollectionView. When I am using Autolayout, my cells won\'t change the size, but their alignment.

Now I would rather want to

Answer 1

swift 4.1

You have 2 ways in order to change the size of CollectionView.
First way -> add this protocol UICollectionViewDelegateFlowLayout
for In my case I want to divided cell into 3 part in one line. I did this code below

extension ViewController: UICollectionViewDelegate, UICollectionViewDataSource ,UICollectionViewDelegateFlowLayout{
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize
    {
            // In this function is the code you must implement to your code project if you want to change size of Collection view
            let width  = (view.frame.width-20)/3
            return CGSize(width: width, height: width)
    }

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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CollectionViewCell", for: indexPath)
        if let label = cell.viewWithTag(100) as? UILabel {
            label.text = collectionData[indexPath.row]
        }
        return cell
    }
}

Second way -> you don't have to add UICollectionViewDelegateFlowLayout but you have to write some code in viewDidload function instead as code below

class ViewController: UIViewController {
@IBOutlet weak var collectionView1: UICollectionView!
        var collectionData = ["1.", "2.", "3.", "4.", "5.", "6.", "7.", "8.", "9.", "10.", "11.", "12."]

    override func viewDidLoad() {
        super.viewDidLoad()
        let width = (view.frame.width-20)/3
        let layout = collectionView.collectionViewLayout as! UICollectionViewFlowLayout
        layout.itemSize = CGSize(width: width, height: width) 
    }
}

extension ViewController: UICollectionViewDelegate, UICollectionViewDataSource {


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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CollectionViewCell", for: indexPath)
        if let label = cell.viewWithTag(100) as? UILabel {
            label.text = collectionData[indexPath.row]
        }

        return cell
    }
}

Whatever you write a code as the first way or second way you will get the same result as above. I wrote it. It worked for me