如何在sizeForItem中獲得自定義集合視圖單元格

Question

如您所知，我們可以使用UICollectionViewDelegateFlowLayout中的sizeForItemAt方法設置UICollectionView單元格的大小。 但是無法獲得具有以下自定義類的單元格。

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
  // This will raise runtime errors.
  let cell = collectionView.cellForItem(at: indexPath) as! MyCustomCell
  // Also this.
  let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "default", for: indexPath) as! MyCustomCell

  return cell.dynamicSize
}

我該怎么辦？

Answer 1

var size = super.collectionView(collectionView, layout: collectionViewLayout, sizeForItemAt: indexPath)

if let cell = collectionView.cellForItem(at: indexPath) as? MyCustomCell {
    size = cell.dynamicSize
}
return size

Answer 2

您可以使用UICollectionViewLayout來做到這一點，例如：

override func viewDidLoad() {
    super.viewDidLoad()

    let customLayout = UICollectionViewFlowLayout()
    customLayout.scrollDirection = .horizontal // .vertical
    customLayout.itemSize = CGSize(width: 100, height: 200) // set the item size here .
    customLayout.sectionInset = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
    customLayout.minimumLineSpacing = 30
    myCollectoinView.collectionViewLayout = customLayout

    let anotherCustomLayout = UICollectionViewFlowLayout()
    anotherCustomLayout....
    myAnotherCollectoinView.collectionViewLayout = anotherCustomlayout
}

如果要使用sizeForItemAt方法 ：

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
      if collectionView == myCollectionView {
         // myCollectionView cell size
         return CGSize(width :100 , height : 100)
      }else { 
         // myAnotherCollectionView cell size
         return CGSize(width: 50 m height : 50)
      }
    }