@IBOutlet weak var constraintTxtV: NSLayoutConstraint!
func TextViewDynamicallyIncreaseSize() {
    let contentSize = self.txtVDetails.sizeThatFits(self.txtVDetails.bounds.size)
    let higntcons = contentSize.height
    constraintTxtV.constant = higntcons
}

extension String {
    func height(withConstrainedWidth width: CGFloat, font: UIFont) -> CGFloat {
        let constraintRect = CGSize(width: width, height: .greatestFiniteMagnitude)
        let boundingBox = self.boundingRect(with: constraintRect, options: .usesLineFragmentOrigin, attributes: [NSFontAttributeName: font], context: nil)
        
        return ceil(boundingBox.height)
    }
    
    func width(withConstraintedHeight height: CGFloat, font: UIFont) -> CGFloat {
        let constraintRect = CGSize(width: .greatestFiniteMagnitude, height: height)
        let boundingBox = self.boundingRect(with: constraintRect, options: .usesLineFragmentOrigin, attributes: [NSFontAttributeName: font], context: nil)
        
        return ceil(boundingBox.width)
    }
}

这是我在Swift 4.1和Xcode 9.4.1中的答案

//This is your label
let proNameLbl = UILabel(frame: CGRect(x: 0, y: 20, width: 300, height: height))
proNameLbl.text = "This is your text"
proNameLbl.font = UIFont.systemFont(ofSize: 17)
proNameLbl.numberOfLines = 0
proNameLbl.lineBreakMode = .byWordWrapping
infoView.addSubview(proNameLbl)

//Function to calculate height for label based on text
func heightForView(text:String, font:UIFont, width:CGFloat) -> CGFloat {
    let label:UILabel = UILabel(frame: CGRect(x: 0, y: 0, width: width, height: CGFloat.greatestFiniteMagnitude))
    label.numberOfLines = 0
    label.lineBreakMode = NSLineBreakMode.byWordWrapping
    label.font = font
    label.text = text

    label.sizeToFit()
    return label.frame.height
}

现在你调用这个函数

//Call this function
let height = heightForView(text: "This is your text", font: UIFont.systemFont(ofSize: 17), width: 300)
print(height)//Output : 41.0

在Swift 5中:

label.textRect(forBounds: label.bounds, limitedToNumberOfLines: 1)

顺便说一下，limitedToNumberOfLines的值取决于你想要的标签文本行。

我无法让@KaanDedeoglu的解决方案在Swift 5中为多行标签和文本视图工作-无论出于什么原因-所以我只是写了一个“手工”解决方案，保持与@KaanDedeoglu的答案中看到的相同的函数签名。在我的程序中就像有魅力一样。

宽度

extension String {

    func width(withConstrainedHeight height: CGFloat, font: UIFont) -> CGFloat {
        
        var wordBoxes = [CGSize]()
        var calculatedHeight = CGFloat.zero
        var calculatedWidth = CGFloat.zero
        
        for word in self.wordsWithWordSeparators() {
            
            let box = word.boundingRect(with: CGSize.zero, attributes: [.font: font], context: nil)
            let boxSize = CGSize(width: box.width, height: box.height)
            wordBoxes.append(boxSize)
            calculatedHeight += boxSize.height
            calculatedWidth = calculatedWidth < boxSize.width ? boxSize.width : calculatedWidth
        }
        
        while calculatedHeight > height && wordBoxes.count > 1 {
            
            var bestLineToRelocate = wordBoxes.count - 1
            
            for i in 1..<wordBoxes.count {
                
                let bestPotentialWidth = wordBoxes[bestLineToRelocate - 1].width + wordBoxes[bestLineToRelocate].width
                let thisPotentialWidth = wordBoxes[i - 1].width + wordBoxes[i].width
                
                if bestPotentialWidth > thisPotentialWidth {
                    bestLineToRelocate = i
                }
            }
            
            calculatedHeight -= wordBoxes[bestLineToRelocate].height
            wordBoxes[bestLineToRelocate - 1].width += wordBoxes[bestLineToRelocate].width
            wordBoxes.remove(at: bestLineToRelocate)
            calculatedWidth = max(wordBoxes[bestLineToRelocate - 1].width, calculatedWidth)
        }
        
        return ceil(calculatedWidth)
    }
}

高度

extension String {
    
    func height(withConstrainedWidth width: CGFloat, font: UIFont) -> CGFloat {
        
        var wordBoxes = [CGSize]()
        var calculatedHeight = CGFloat.zero
        var currentLine = 0
        
        for word in self.wordsWithWordSeparators() {
            
            let box = word.boundingRect(with: CGSize.zero, attributes: [.font: font], context: nil)
            let boxSize = CGSize(width: box.width, height: box.height)
            
            if wordBoxes.isEmpty == true {
                wordBoxes.append(boxSize)
            }
            else if wordBoxes[currentLine].width + boxSize.width > width {
                wordBoxes.append(boxSize)
                currentLine += 1
            }
            else {
                wordBoxes[currentLine].width += boxSize.width
                wordBoxes[currentLine].height = max(wordBoxes[currentLine].height, boxSize.height)
            }
        }
        
        for wordBox in wordBoxes {
            calculatedHeight += wordBox.height
        }
        
        return calculatedHeight
    }
}

使用的辅助方法

extension String {
    
    // Should work with any language supported by Apple
    func wordsWithWordSeparators () -> [String] {
        
        let range = self.startIndex..<self.endIndex
        var words = [String]()
        
        self.enumerateSubstrings(in: range, options: .byWords) { (substr, substrRange, enclosingRange, stop) in
            let wordWithWordSeparators = String(self[enclosingRange])
            words.append(wordWithWordSeparators)
        }
        
        return words
    }
}

注意:这些高度和宽度计算假设给定的标签或文本视图在执行换行时不会拆分或连字符。如果这不是你的情况，你应该只用文字来代替字符。此外，如果您处于运行时敏感的环境中，可能需要考虑限制这些函数调用或缓存结果，因为根据字符串包含的单词数量，它们的开销可能会有点大。

这里有一个简单的解决方案，对我来说很有用。类似于其他发布的一些，但它不需要sizeToFit

注意这是用Swift 5写的

let lbl = UILabel()
lbl.numberOfLines = 0
lbl.font = UIFont.systemFont(ofSize: 12) // make sure you set this correctly 
lbl.text = "My text that may or may not wrap lines..."

let width = 100.0 // the width of the view you are constraint to, keep in mind any applied margins here
 
let height = lbl.systemLayoutSizeFitting(CGSize(width: width, height: UIView.layoutFittingCompressedSize.height), withHorizontalFittingPriority: .required, verticalFittingPriority: .fittingSizeLevel).height

它处理行换行等。不是最优雅的代码，但它完成了工作。