swift - 将“UICollectionReusableView”类型的值转换为“MyApp.CSSectionHeader”时出错

Question

我有以下课程：

class CSSectionHeader: UICollectionReusableView {

    @IBOutlet var textLabel: UILabel!

}

然后，我尝试将其投射如下：

override func collectionView(collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, atIndexPath indexPath: NSIndexPath) -> UICollectionReusableView {

    let cell1 = UICollectionReusableView()

    if (kind == UICollectionElementKindSectionHeader) {
        // Throws the cast error here:
        let cell: CSSectionHeader = collectionView.dequeueReusableSupplementaryViewOfKind(kind, withReuseIdentifier: "sectionHeader", forIndexPath: indexPath) as! CSSectionHeader

        return cell
    } else if (kind == CSStickyHeaderParallaxHeader) {
        let cell: UICollectionReusableView = collectionView.dequeueReusableSupplementaryViewOfKind(kind, withReuseIdentifier: "header", forIndexPath: indexPath) as! UICollectionReusableView

        return cell
    }

    return cell1
}

问题是我收到以下错误：

Could not cast value of type 'UICollectionReusableView' (0x10ff4d140) to 'MyApp.CSSectionHeader' (0x10d775a70).

Answer 1

为了能够 deque 自定义类的标头，您必须在调用之前在 collectionview 中注册此类dequeueReusableSupplementaryViewOfKind。

这应该看起来像：

self.collectionView.registerClass(CSSectionHeader.self,
    forSupplementaryViewOfKind: UICollectionElementKindSectionHeader, 
    withReuseIdentifier: "sectionHeader")

你可以把它放在里面viewDidLoad()

Answer 2

您还可以为情节提要中的标题设置自定义类。如果您通过扩展添加流布局委托，这会派上用场。

Answer 3

viewDidLoad() 中的 Swift 3

self.collectionView.registerClass(CSSectionHeader.self,
forSupplementaryViewOfKind: UICollectionElementKindSectionHeader, 
withReuseIdentifier: "sectionHeader")

还添加以下内容

func collectionView(_ collectionView: UICollectionView,
                    viewForSupplementaryElementOfKind kind: String,
                    at indexPath: IndexPath) -> UICollectionReusableView{
    let headerView: CSSectionHeader  = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier:"sectionHeader", for: indexPath) as! CSSectionHeader
    return headerView }