ios - 如何找到 UILabel 的实际行数？

Question

在使用 text 和 font 初始化 UILabel 之后，如何找到它的实际 行数？我已将其 numberOfLines 属性设置为 0，因此它将扩展到需要的行数。但是，我怎么才能知道在我设置了它的text之后它最终得到了多少行呢？

我发现了类似的问题，但似乎没有一个提供简明的答案，在我看来，它一定很容易得到它，而无需在使用 boundingRectWithSize 或 时产生任何开销sizeWithFont,...

Answer 1

这些都不适合我。下面一个做了，

swift 4.2:

extension UILabel {
    func calculateMaxLines() -> Int {
        let maxSize = CGSize(width: frame.size.width, height: CGFloat(Float.infinity))
        let charSize = font.lineHeight
        let text = (self.text ?? "") as NSString
        let textSize = text.boundingRect(with: maxSize, options: .usesLineFragmentOrigin, attributes: [NSAttributedString.Key.font: font], context: nil)
        let linesRoundedUp = Int(ceil(textSize.height/charSize)) 
        return linesRoundedUp
    }    
}

swift 4/4.1:

extension UILabel {

    func calculateMaxLines() -> Int {
        let maxSize = CGSize(width: frame.size.width, height: CGFloat(Float.infinity))
        let charSize = font.lineHeight
        let text = (self.text ?? "") as NSString
        let textSize = text.boundingRect(with: maxSize, options: .usesLineFragmentOrigin, attributes: [.font: font], context: nil)
        let linesRoundedUp = Int(ceil(textSize.height/charSize)) 
        return linesRoundedUp
    }

}

swift 3:

extension UILabel {

    func calculateMaxLines() -> Int {
        let maxSize = CGSize(width: frame.size.width, height: CGFloat(Float.infinity))
        let charSize = font.lineHeight
        let text = (self.text ?? "") as NSString
        let textSize = text.boundingRect(with: maxSize, options: .usesLineFragmentOrigin, attributes: [NSFontAttributeName: font], context: nil)
        let linesRoundedUp = Int(ceil(textSize.height/charSize)) 
        return linesRoundedUp
    }

}