使用自动调整大小功能时，UICollectionView单元格不会根据单元格内容调整大小

class MyCollectionViewFlowLayout: UICollectionViewFlowLayout {
    override init() {
        super.init()
        estimatedItemSize = UICollectionViewFlowLayoutAutomaticSize
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        estimatedItemSize = UICollectionViewFlowLayoutAutomaticSize
    }
}

class MyViewController: UIViewController, UICollectionViewDelegateFlowLayout {
    // ...
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        // 根据单元格的内容计算并返回所需的大小
        let item = items[indexPath.item]
        let text = item.text
        let size = text.size(withAttributes: [NSAttributedString.Key.font: UIFont.systemFont(ofSize: 17)])
        return CGSize(width: size.width + 20, height: size.height + 20)
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, estimatedSizeForItemAt indexPath: IndexPath) -> CGSize {
        // 返回一个估计的大小作为占位符
        return CGSize(width: 100, height: 100)
    }
    
    // ...
}