swift - 如何安全地解开 header 值

Question

我的应用程序崩溃，因为在解包值“ header ”时发现 nil 我尝试使用guard let 语句，尽管它不起作用，安全解包该值的最佳方法是什么？

override func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {

    self.headerOpen = true

    if self.headerOpen == true {

      let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: headerId, for: indexPath) as! HomePageHeader

    header.currentUser = self.currentUser
    header.usersLocation = self.usersLocation
    header.delegate = self

    reloadInputViews()

    } else if headerOpen == false {


        print("header open is false")

        }




    return header!

}

Answer 1

if let ... 或 guard let ... 可以帮助您。例如:

if let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: headerId, for: indexPath) as? HomePageHeader {
    print("header unwrapped")
}

或

guard let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: headerId, for: indexPath) as? HomePageHeader else { print("header not unwrapped") }
print("header unwrapped")