在collectionview中计算高度时，ios swift index 0超出了空数组的范围

Question

我想计算 HTML 字符串上 Collection View 单元格的高度。 HTML 字符串通过底部扩展名转换为字符串。但是在运行时出现此错误并崩溃:

*** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndexedSubscript:]: index 0 beyond bounds for empty array'

我的代码:

extension String {
    var htmlToAttributedString: NSAttributedString? {
        guard let data = data(using: .utf8) else { return NSAttributedString() }
        do {
            return try NSAttributedString(data: data, options: [.documentType: NSAttributedString.DocumentType.html, .characterEncoding:String.Encoding.utf8.rawValue], documentAttributes: nil)
        } catch {
            return NSAttributedString()
        }
    }
    var htmlToString: String {
        return htmlToAttributedString?.string ?? ""
    }
}

在方法 cellForItemAt :

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    //let cell  = ....
    cell?.biographyTextView.text = artistModel?.biography?.htmlToString
}

在方法 sizeForItemAt

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    let htmlToString = artistModel?.biography?.htmlToString
    let size = CGSize(width: collectionView.frame.width, height: .greatestFiniteMagnitude)
    let attributes = [NSAttributedStringKey.font: UIFont.systemFont(ofSize: 15)]
    let estimatedFrame = NSString(string: htmlToString!).boundingRect(with: size, options: [.usesFontLeading, .usesLineFragmentOrigin], attributes: attributes, context: nil)
    return CGSize(width: collectionView.frame.width, height: estimatedFrame.height)
}

传记文本例如:

<p>blahblah><br /><br/><li>asd</li>....

Answer 1

清理这个。改变:

let htmlToString = artistModel?.biography?.htmlToString

到:

guard let artist = artistModel, let biblio = artist.biography else {return a default size}

let htmlToString = biblio.htmlToString