Resize font along with frame of label using pinch gesture on UILabel?

问题

Increase or decrease font size smoothly whenever user resize label using pinch gesture on it.

Note

Without compromising quality of font
Not only transforming the scale of UILabel
With support of multiline text
Rotation gesture should work proper with pinch gesture
Reference: SnapChat or Instagram Text Editor tool

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: [NSAttributedStringKey.font: UIFont(name: font.fontName, size: font.pointSize)!], context: nil)
        return ceil(boundingBox.height)
    }

    func width(withConstrainedHeight height: CGFloat, font: UIFont) -> CGFloat {
        let constraintRect = CGSize(width: .greatestFiniteMagnitude, height: height)
        let boundingBox = self.boundingRect(with: constraintRect, options: .usesLineFragmentOrigin, attributes: [NSAttributedStringKey.font: UIFont(name: font.fontName, size: font.pointSize)!], context: nil)
        return ceil(boundingBox.width)
    }
}

func resizeLabelToText(textLabel : UILabel)
{
    let labelFont = textLabel.font
    let labelString = textLabel.text
    let labelWidth : CGFloat = labelString!.width(withConstrainedHeight: textLabel.frame.size.height, font: labelFont!)
    let labelHeight : CGFloat = labelString!.height(withConstrainedWidth: labelWidth, font: labelFont!)

    textLabel.frame = CGRect(x: textLabel.frame.origin.x, y: textLabel.frame.origin.y, width: labelWidth, height: labelHeight)
    textLabel.font = labelFont
}

func pinchedRecognize(_ pinchGesture: UIPinchGestureRecognizer) {
    guard pinchGesture.view != nil else {return}

    if (pinchGesture.view is UILabel) {
        let selectedTextLabel = pinchGesture.view as! UILabel

        if pinchGesture.state == .began || pinchGesture.state == .changed {
            let pinchScale = round(pinchGesture.scale * 1000) / 1000.0
            if (pinchScale < 1) {
                selectedTextLabel.font = selectedTextLabel.font.withSize(selectedTextLabel.font.pointSize - pinchScale)
            }
            else {
                selectedTextLabel.font = selectedTextLabel.font.withSize(selectedTextLabel.font.pointSize + pinchScale)
            }
            resizeLabelToText(textLabel: selectedTextLabel)
        }
    }
}

回答1:

I solved the problem with following code which is working fine with every aspect which are mentioned in question, similar to Snapchat and Instagram:

var pointSize: CGFloat = 0
@objc func pinchRecoginze(_ pinchGesture: UIPinchGestureRecognizer) {
    guard pinchGesture.view != nil else {return}

    let view = pinchGesture.view!
    if (pinchGesture.view is UILabel) {
        let textLabel = view as! UILabel

        if pinchGesture.state == .began {
            let font = textLabel.font
            pointSize = font!.pointSize

            pinchGesture.scale = textLabel.font!.pointSize * 0.1
        }
        if 1 <= pinchGesture.scale && pinchGesture.scale <= 10  {
            textLabel.font = UIFont(name: textLabel.font!.fontName, size: pinchGesture.scale * 10)

            resizeLabelToText(textLabel: textLabel)
        }
    }
}

func resizeLabelToText(textLabel : UILabel) {
    let labelSize = textLabel.intrinsicContentSize
    textLabel.bounds.size = labelSize
}

回答2:

Call following method every time after UILabel size changes.

func labelSizeHasBeenChangedAfterPinch(_ label:UILabel, currentSize:CGSize){
        let MAX = 25
        let MIN = 8
        let RATE = -1
        for proposedFontSize in stride(from: MAX, to: MIN, by: RATE){
            let options = NSStringDrawingOptions.usesFontLeading.union(.usesLineFragmentOrigin)
            let attribute = [NSAttributedString.Key.font:UIFont.systemFont(ofSize: CGFloat(proposedFontSize))]
            // let context = IF NEEDED ...
            let rect =  NSString(string: label.text ?? "").boundingRect(with: currentSize, options: options, attributes: attribute, context: nil)
            let labelSizeThatFitProposedFontSize = CGSize(width: rect.width , height: rect.height)
            if (currentSize.height > labelSizeThatFitProposedFontSize.height) && (currentSize.width > labelSizeThatFitProposedFontSize.width){
                DispatchQueue.main.async {
                    label.font = UIFont.systemFont(ofSize: CGFloat(proposedFontSize))
                }
                break
            }
        }
    }