ios - CATextLayer 渲染具有截断和段落样式的 AttributedString

Question

我正在尝试创建一个具有动画属性的自定义标签，所以我决定使用 CATextLayer 而不是直接使用 CoreText..

我想出了下面的代码(我用 playground 来测试东西):

//: A UIKit based Playground for presenting user interface
  
import UIKit
import PlaygroundSupport


public extension CGRect {
    public static func centerRect(_ rectToCenter: CGRect, in rect: CGRect) -> CGRect {
        return CGRect(x: rect.origin.x + ((rect.width - rectToCenter.width) / 2.0),
                      y: rect.origin.y + ((rect.height - rectToCenter.height) / 2.0),
                      width: rectToCenter.width,
                      height: rectToCenter.height)
    }
}

class MyLabel : UIView {
    private let textLayer = CATextLayer()
    public var textColor: UIColor = UIColor.black
    public var font: UIFont = UIFont.systemFont(ofSize: 17.0)
    private var _lineBreak: NSLineBreakMode = .byTruncatingTail

    
    init() {
        super.init(frame: .zero)
        self.text = nil
        self.textAlignment = .natural
        self.lineBreakMode = .byTruncatingTail
        self.textLayer.isWrapped = true
        
        self.layer.addSublayer(self.textLayer)
    }
    
    @available(*, unavailable)
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    
    //Update the CATextLayer's attributed string when this property is set..
    public var text: String? {

        //Getter just returns the CATextLayer's string
        get {
            if let attrString = self.textLayer.string as? NSAttributedString {
                return attrString.string
            }
            
            return self.textLayer.string as? String
        }
        
        //Setter creates an attributed string with paragraph style..
        //Font and colour..
        set {
            if let value = newValue {
                let paragraphStyle = NSParagraphStyle.default.mutableCopy() as! NSMutableParagraphStyle
                paragraphStyle.alignment = self.textAlignment
                paragraphStyle.lineBreakMode = self.lineBreakMode
                
                self.textLayer.string = NSMutableAttributedString(string: value, attributes: [
                    .foregroundColor: self.textColor,
                    .font: self.font])
            }
            else {
                self.textLayer.string = nil
            }
        }
    }
    
    //Convert NSTextAlignment to kCAAlignment String for CATextLayer
    public var textAlignment: NSTextAlignment {
        get {
            switch self.textLayer.alignmentMode {
            case kCAAlignmentLeft:
                return .left
                
            case kCAAlignmentCenter:
                return .center
                
            case kCAAlignmentRight:
                return .right
                
            case kCAAlignmentJustified:
                return .justified
                
            default:
                return .natural
            }
        }
        
        set {
            switch newValue {
            case .left:
                self.textLayer.alignmentMode = kCAAlignmentLeft
                
            case .center:
                self.textLayer.alignmentMode = kCAAlignmentCenter
                
            case .right:
                self.textLayer.alignmentMode = kCAAlignmentRight
                
            case .justified:
                self.textLayer.alignmentMode = kCAAlignmentJustified
                
            default:
                self.textLayer.alignmentMode = kCAAlignmentNatural
            }
        }
    }
    
    //Convert NSLineBreakMode to kCAAlignmentMode String
    public var lineBreakMode: NSLineBreakMode {
        get {
            return _lineBreak
        }
        
        set {
            _lineBreak = newValue
            
            switch newValue {
            case .byWordWrapping:
                self.textLayer.isWrapped = true
                self.textLayer.truncationMode = kCATruncationNone
                
            case .byCharWrapping:
                self.textLayer.isWrapped = true
                self.textLayer.truncationMode = kCATruncationNone
                
            case .byClipping:
                self.textLayer.isWrapped = false
                self.textLayer.truncationMode = kCATruncationNone
                
            case .byTruncatingHead:
                self.textLayer.truncationMode = kCATruncationStart
                
            case .byTruncatingMiddle:
                self.textLayer.truncationMode = kCATruncationMiddle
                
            case .byTruncatingTail:
                self.textLayer.truncationMode = kCATruncationEnd
            }
        }
    }
    
    
    //Override layoutSubviews to render the CATextLayer..
    internal override func layoutSubviews() {
        super.layoutSubviews()
        
        //Calculate attributed string size..
        let string = self.textLayer.string as! NSAttributedString
        var rect = string.boundingRect(with: self.bounds.size, options: [.usesLineFragmentOrigin, .usesFontLeading], context: nil)

        //If you change dy to 1.0, Text will render weirdly!
        rect = rect.insetBy(dx: 0.0, dy: 0.0)
        
        //Render the textLayer by centering it in its parent..
        self.textLayer.contentsScale = UIScreen.main.scale
        self.textLayer.rasterizationScale = UIScreen.main.scale
        self.textLayer.frame = CGRect.centerRect(rect, in: self.bounds)
        self.textLayer.backgroundColor = UIColor.lightGray.cgColor
    }
    
    //Somehow always returns 21.. ={
    //Not used right now because it doesn't work.. at all..
    private func sizeOfTextThatFits(size: CGSize) -> CGSize {
        if let string = self.textLayer.string as? NSAttributedString {
            let path = CGMutablePath()
            path.addRect(CGRect(x: 0.0, y: 0.0, width: size.width, height: size.height))
            
            let frameSetter = CTFramesetterCreateWithAttributedString(string as CFAttributedString)
            let frame = CTFramesetterCreateFrame(frameSetter, CFRangeMake(0, 0), path, nil)
            let lines = CTFrameGetLines(frame) as NSArray
            
            var lineWidth: CGFloat = 0.0
            var yOffset: CGFloat = 0.0
            
            for line in lines {
                let ctLine = line as! CTLine
                var ascent: CGFloat = 0.0
                var descent: CGFloat = 0.0
                var leading: CGFloat = 0.0
                lineWidth = CGFloat(max(CTLineGetTypographicBounds(ctLine, &ascent, &descent, &leading), Double(lineWidth)))
                yOffset += ascent + descent + leading;
            }
            return CGSize(width: lineWidth, height: yOffset)
        }
        return .zero
    }
}


class MyViewController : UIViewController {
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white

        let label = MyLabel()
        label.backgroundColor = UIColor.red
        label.frame = CGRect(x: 150, y: 200, width: 200, height: 200)
        label.text = "Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!Hello World! Hello World! Hello World! Hello World! Hello World! Hello World!"
        label.textColor = .black
        
        view.addSubview(label)
        self.view = view
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()

问题是，如果我使用 NSParagraphStyle，它根本不会正确渲染或计算大小!

如果我删除段落样式，它可以很好地呈现，但从不遵守换行模式，并且大小不正确..

知道我做错了什么吗？我怎样才能让它服从段落样式的换行模式？为什么在应用段落样式时它总是计算大小为 21？

使用段落样式时:

删除段落样式时:

当删除段落样式但在 CATextLayer 上设置 TruncateEnd 时(它永远不会截断并且最后一行与倒数第二行之间的间距更大):

Answer 1

我发现结束省略号字形不是从属性字符串中获取它的大小，而是从 CATextLayer.fontSize 属性中获取它的大小。

这似乎默认为一个很大的值，这解释了您的文本在您的第一个示例中被向下移动和剪裁。向下扩展文本层的框架大小，设置CATextLayer 的isWrapped=false，您将看到您的文本加上一个巨大的...省略号字形!

设置 CATextLayer.fontSize 以匹配属性文本的字体大小可以解决此问题，但它看起来像是一个 Apple 错误。

我也无法通过单独设置属性字符串属性来使其工作..