CTLineDraw细节绘制
首先得了解字形，如下图：
字形图.png
步骤
1.
CTFrameGetLines函数获取行数
2.CTFrameGetLineOrigins函数获取每行的坐标
3.CTLineGetTypographicBounds(line as! CTLine, &lineAscent, &lineDescent, &lineLeading)获得每行的字形
4.根据实际情况微调坐标
CGContextSetTextPosition(ctx, lineOrigin.x, lineOrigin.y)
5.CTLineDraw(line as! CTLine, ctx)绘制某一行。
首先绘制大多数情况都要需要高度，那么现在来一个高度计算的大致思路:
/*
根据属性字符串计算绘制所需要的高度
思路就是 lineAscent＋lineDescent ＋lineLeading代表一行的高度，分别对每一行进行高度累加
*/
func getDisplayHeight(attributeStr: NSAttributedString,width:CGFloat) -> CGFloat{
let ctFrameSetter = CTFramesetterCreateWithAttributedString(attributeStr)
//建议的宽高
let suggestSize = CTFramesetterSuggestFrameSizeWithConstraints(ctFrameSetter, CFRangeMake(0, attributeStr.length), nil, CGSize(width: width, height: CGFloat.max), nil)
let path = CGPathCreateMutable()
CGPathAddRect(path, nil, CGRect(x: 0, y: 0, width: width, height: suggestSize.height*2))//2是假的，只是防止画布不够大，计算有误，下面才开始精确计算高度
let ctFrame = CTFramesetterCreateFrame(ctFrameSetter, CFRangeMake(0, 0), path, nil)
let lines = CTFrameGetLines(ctFrame) as Array
var lineOrigins = Array(count: lines.count, repeatedValue: CGPointZero)//获取每一个行的坐标
CTFrameGetLineOrigins(ctFrame, CFRangeMake(0, 0), &lineOrigins)
var lineAscent:CGFloat = 0
var lineDescent:CGFloat = 0
var lineLeading:CGFloat = 0
var lineTotalHeight:CGFloat = 0
for (_,line) in lines.enumerate() {
CTLineGetTypographicBounds(line as! CTLine, &lineAscent, &lineDescent, &lineLeading)
let oneLineHeight = lineAscent+lineDescent + lineLeading//这里可以接上细节微调，来返回高度
lineTotalHeight += oneLineHeight
}
//高度就这么计算好了
return lineTotalHeight
}
CTLineDraw绘制，就是将CTFrameDraw拆分而已
override func drawInContext(ctx: CGContext) {
super.drawInContext(ctx)
//坐标系转换
CGContextSetTextMatrix(ctx, CGAffineTransformIdentity)
CGContextTranslateCTM(ctx, 0, self.bounds.size.height)
CGContextScaleCTM(ctx, 1.0, -1.0)
//创建绘制的区域
let path = CGPathCreateMutable()
CGPathAddRect(path, nil, self.bounds)
// 4.创建需要绘制的文字
let attributed = NSMutableAttributedString(string: "估后共和国开不开vbdkaph估后共和国开不开vbdkaph️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️这是我的第一个coreText demo，我是要给兵来自老白干I型那个饿哦个呢给个I类回滚igkhpwfh 评估后共和国开不开vbdkaphphohghg 的分工额好几个辽宁省更怕hi维护你不看hi好人佛【井柏然把饿哦个️");
attributed.addAttribute(NSFontAttributeName, value: UIFont.systemFontOfSize(20), range: NSMakeRange(0, 5));
attributed.addAttribute(NSForegroundColorAttributeName, value: UIColor.redColor(), range: NSMakeRange(3, 10));
attributed.addAttribute(NSForegroundColorAttributeName, value: UIColor.orangeColor(), range: NSMakeRange(0, 2));
//创建段落属性
let paraStyle = NSMutableParagraphStyle()
attributed.addAttribute(NSParagraphStyleAttributeName, value: paraStyle, range: NSMakeRange(0, attributed.length))
//根据计算的高度画一个比边框 start
let strockeHegith = self.getDisplayHeight(attributed, width: ScreenWidth)
CGContextSaveGState(ctx)
CGContextSetTextMatrix(ctx, CGAffineTransformIdentity)
CGContextTranslateCTM(ctx, 0, self.bounds.size.height)
CGContextScaleCTM(ctx, 1.0, -1.0)
let strokePath = CGPathCreateMutable()
CGPathAddRect(strokePath, nil, CGRect(x: 1, y: 1, width: ScreenWidth-2, height: strockeHegith))
CGContextAddPath(ctx, strokePath)
CGContextSetStrokeColorWithColor(ctx, UIColor.purpleColor().CGColor)
CGContextStrokePath(ctx)
CGContextRestoreGState(ctx)
//根据计算的高度画一个比边框 end
let ctFrameSetter = CTFramesetterCreateWithAttributedString(attributed)
let ctFrame = CTFramesetterCreateFrame(ctFrameSetter, CFRangeMake(0, attributed.length), path, nil)
let lines = CTFrameGetLines(ctFrame) as NSArray
var originsArray = Array(count: lines.count, repeatedValue: CGPointZero)//用于存储每一行的坐标
CTFrameGetLineOrigins(ctFrame, CFRangeMake(0, 0), &originsArray)
var frameY:CGFloat = 0
let kGlobalLineLeading:CGFloat = 0
for (i,line) in lines.enumerate() {
var lineAscent:CGFloat = 0
var lineDescent:CGFloat = 0
var lineLeading:CGFloat = 0
CTLineGetTypographicBounds(line as! CTLine, &lineAscent, &lineDescent, &lineLeading)
var lineOrigin = originsArray[i];
if (i > 0)
{
frameY = frameY - kGlobalLineLeading - lineAscent;//减去一个行间距，再减去第二行，字形的上部分 （循环）
lineOrigin.y = frameY;
} else
{
frameY = lineOrigin.y;
}
// 调整成所需要的坐标
CGContextSetTextPosition(ctx, lineOrigin.x, lineOrigin.y);
CTLineDraw(line as! CTLine, ctx);
frameY = frameY - lineDescent//说明下这里，就是减去字形下面部分
}
}
效果图如下
总结：因为有中文，英文和表情的存在，默认情况下这三种的行高都是不等的，可以用上面的方法微调行高，使其所有情况下都是等高的。
为所需显示的最后一行添加省略号
步骤：
1.获取所需操作行的range
2.获取需要干掉字符的属性
3.将获取的属性，添加给省略号属性
4.剩下的字符串拼接上省略号
5.创建一个全新的CTLine绘制
6.绘制CTLine
mark:7.别傻傻的，省略号在这里就是一个表示，可以用是任何东西
//处理最后一行，将最后一个字符干掉，并且加上省略号
let lCharacter = "……"
if i == lines.count - 1 {
let lastLineRange = CTLineGetStringRange(line as! CTLine)
let lastCharAttribute = attributed.attributesAtIndex(attributed.length - 1, effectiveRange: nil)
let lastAppentAttributeStr = NSAttributedString(string: lCharacter, attributes: lastCharAttribute)
let foreAttributeStr = attributed.attributedSubstringFromRange(NSMakeRange(lastLineRange.location, lastLineRange.length - 2)) as! NSMutableAttributedString//这里减去2是因为后面有个结尾的符号，c语言里面的“/n”
let afterAttributeStr = attributed.attributedSubstringFromRange(NSMakeRange(lastLineRange.location + lastLineRange.length - 1, 1)) as! NSMutableAttributedString
print("after:\\(afterAttributeStr.string)测试")
foreAttributeStr.appendAttributedString(lastAppentAttributeStr)
let createLastline = CTLineCreateWithAttributedString(foreAttributeStr)
CTLineDraw(createLastline, ctx)
}else{
CTLineDraw(line as! CTLine, ctx)
}