CoreText的认识（二）

1.创建CTRunDelegate

• 创建CTRunDelegate对象，并且传递callback和参数

    var imageName = "e_banner"
    var imageCallBack = CTRunDelegateCallbacks(version: kCTRunDelegateVersion1, dealloc: { (_) in
        print("-------")
    }, getAscent: { (ascent) -> CGFloat in
        return 80
    }, getDescent: { (descent) -> CGFloat in
        return 0
    }) { (width) -> CGFloat in
        return 200
    }
    let runDelegate = CTRunDelegateCreate(&imageCallBack, &imageName)
  

• 创建一个富文本类型的图片占位图，绑定代理

    let imageString = NSMutableAttributedString(string: " ")
    imageString.addAttribute(NSAttributedString.Key(rawValue: kCTRunDelegateAttributeName as String), value: runDelegate!, range: NSRange(location: 0, length: 1))
    imageString.addAttribute(NSAttributedString.Key.init(rawValue: "imageName"), value: imageName, range: NSRange(location: 0, length: 1))
  

• 将图片占位符插入到我们的富文本中

    attString.insert(imageString, at: 14)
  

2.通过遍历CTLine中的CTRun计算图片所在位置

• 首先遍历CTLine

• 遍历每个Line下的CTRun

• 拿到每个CTRun的attribute属性，并判断代理是否为空，文字的代理为空，而图片代理是不为空的；

• 计算CTRun的frame

• 通过CTLine获取对应的原点，CTRunGetTypographicBounds获取宽和ascent，descent;

    // 处理绘制图片的逻辑
    let lines = CTFrameGetLines(frame) as Array
    var originsArrays = [CGPoint](repeating: CGPoint.zero, count: lines.count)
    let range = CFRangeMake(0, 0)
    CTFrameGetLineOrigins(frame, range, &originsArrays)
    for i in 0..<lines.count {
        let line = lines[i]
  
        let runs = CTLineGetGlyphRuns(line as! CTLine) as Array
  
        for j in 0..<runs.count {
            
            let run = runs[j]
            
            let attributes = CTRunGetAttributes(run as! CTRun) as NSDictionary
            
            if attributes.value(forKey: kCTRunDelegateAttributeName as String) == nil {
                continue
            }
    
            if let imageUrlStr = attributes["imageName"] as? String, let image = UIImage(named: imageUrlStr) {
                
                var runAscent = CGFloat()
                var runDescent = CGFloat()
                let lineOrigin = originsArrays[i]
                
                let width = CTRunGetTypographicBounds(run as! CTRun, CFRangeMake(0, 0), &runAscent, &runDescent, nil)
                
                let runRect = CGRect(x: lineOrigin.x + CTLineGetOffsetForStringIndex(line as! CTLine, CTRunGetStringRange(run as! CTRun).location, nil), y: lineOrigin.y - runDescent, width: CGFloat(width), height: runAscent + runDescent)
                
                imageFrame = runRect
                
                context?.draw(image.cgImage!, in: runRect)
            }
        }
    }