首先创建协议前加上@objc ，可选的方法前面加上@objc optional，必须实现的不需要加

@objc protocol PhotoPickerCollectionViewCellDelegate: NSObjectProtocol {
     @objc optional func photoPickerCollectionViewCellAddPhotoBtnClick(cell: PhotoPickerCollectionViewCell)
}

class PhotoPickerCollectionViewCell: UICollectionViewCell {
    weak var delegate: PhotoPickerCollectionViewCellDelegate?
    
    @IBAction func addPhotoBtn(_ sender: Any) {
        delegate?.photoPickerCollectionViewCellAddPhotoBtnClick?(cell: self)
    }
}

实现协议

extension PhotoPickerCollectionViewController: PhotoPickerCollectionViewCellDelegate {
    func photoPickerCollectionViewCellAddPhotoBtnClick(cell: PhotoPickerCollectionViewCell) {
        print("")
    }
}

最后别忘记设置代理，就这些吧！