您需要使用另一个 CAShapeLayer 来表示毕业线，并使用 CATextLayer 表示毕业结束时的文字。
与其像my answer here 那样进行核心图形绘制，我建议您使用 100% 分层方法以最适合您现有的代码。
这样的事情应该可以解决问题：
func drawSemicircle() {
// drawing an upper half of a circle -> 180 degree to 0 degree, clockwise
let startAngle = CGFloat(M_PI)
let endAngle = CGFloat(0.0)
let centerPoint = CGPoint(x: CGRectGetWidth(frame)*0.5 , y: CGRectGetHeight(frame))
let radius = frame.size.width*0.5 - 80.0 // radius of your arc
// path set here
let semiCircleLayer = CAShapeLayer()
semiCircleLayer.frame = bounds // requried for layer calculations
let semiCirclePath = UIBezierPath(arcCenter:centerPoint, radius:radius, startAngle:startAngle, endAngle:endAngle, clockwise: true)
semiCircleLayer.path = semiCirclePath.CGPath
// layer customisation
semiCircleLayer.fillColor = UIColor.clearColor().CGColor
semiCircleLayer.strokeColor = UIColor(red: 237.0/255.0, green: 236.0/255.0, blue: 236.0/255.0, alpha: 1.0).CGColor
semiCircleLayer.lineWidth = 20.0
semiCircleLayer.lineCap = kCALineCapButt
layer.addSublayer(semiCircleLayer)
// draw graduation (cue the wall of code!)
let graduationLayer = CAShapeLayer() // the graduation layer that'll display the graduation
graduationLayer.frame = semiCircleLayer.bounds
let graduationWidth = CGFloat(4.0) // the width of the graduation
let graduationLength = CGFloat(50.0) // the length of the graduation
let graduationColor = UIColor.redColor() // the color of both the graduation line and text
let startGradRad = radius-semiCircleLayer.lineWidth*0.5 // the starting radius of the graduation
let endGradRad = startGradRad+graduationLength // the ending radius of the graduation
let graduationAngle = CGFloat(M_PI*0.79) // 21% along the arc from the left (0 degrees coresponds to the right hand side of the circle, with the positive angle direction going anti-clocwise (much like a unit circle in maths), so we define 79% along the arc, from the right hand side)
// the starting point of the graduation line. the angles are negative as the arc is effectively drawn upside-down in the UIKit coordinate system.
let startGradPoint = CGPoint(x: cos(-graduationAngle)*startGradRad+centerPoint.x, y: sin(-graduationAngle)*startGradRad+centerPoint.y)
let endGradPoint = CGPoint(x: cos(-graduationAngle)*endGradRad+centerPoint.x, y: sin(-graduationAngle)*endGradRad+centerPoint.y)
// the path for the graduation line
let graduationPath = UIBezierPath()
graduationPath.moveToPoint(startGradPoint) // start point
graduationPath.addLineToPoint(endGradPoint) // end point
graduationLayer.path = graduationPath.CGPath // add path to the graduation shape layer
// configure stroking options
graduationLayer.fillColor = UIColor.clearColor().CGColor
graduationLayer.strokeColor = graduationColor.CGColor
graduationLayer.lineWidth = graduationWidth
// add to semi-circle layer
semiCircleLayer.addSublayer(graduationLayer)
// the font of the text to render at the end of the graduation
let textFont = UIFont.systemFontOfSize(30)
// the text to render at the end of the graduation - do you custom value logic here
let str : NSString = "value"
// default paragraph style
let paragraphStyle = NSParagraphStyle()
// the text attributes dictionary. used to obtain a size of the drawn text in order to calculate its frame
let textAttributes = [NSParagraphStyleAttributeName:paragraphStyle, NSFontAttributeName:textFont]
// size of the rendered text
let textSize = str.sizeWithAttributes(textAttributes)
let xOffset = abs(cos(graduationAngle))*textSize.width*0.5 // the x-offset of the text from the end of the graduation line
let yOffset = abs(sin(graduationAngle))*textSize.height*0.5 // the y-offset of the text from the end of the graduation line
/// the padding between the graduation line and the text
let graduationTextPadding = CGFloat(5.0)
// bit of pythagorus to determine how far away the center of the text lies from the end of the graduation line. multiplying the values together is cheaper than using pow. the text padding is added onto it.
let textOffset = sqrt(xOffset*xOffset+yOffset*yOffset)+graduationTextPadding
// the center of the text to render
let textCenter = CGPoint(x: cos(-graduationAngle)*textOffset+endGradPoint.x, y: sin(-graduationAngle)*textOffset+endGradPoint.y)
// the frame of the text to render
let textRect = CGRect(x: textCenter.x-textSize.width*0.5, y: textCenter.y-textSize.height*0.5, width: textSize.width, height: textSize.height)
let textLayer = CATextLayer()
textLayer.contentsScale = UIScreen.mainScreen().scale // to ensure the text is rendered at the screen scale
textLayer.frame = textRect
textLayer.string = str
textLayer.font = textFont
textLayer.fontSize = textFont.pointSize // required as CATextLayer ignores the font size of the font you pass
textLayer.foregroundColor = graduationColor.CGColor // color of text
graduationLayer.addSublayer(textLayer)
}
输出：
这里有很多代码，因为您必须执行一些额外的逻辑才能计算CATextLayer 的大小。您可以通过使用UILabel 来简化此操作，因为您可以使用sizeToFit 来计算大小，但这可能会使层层次结构复杂化。
我已尽力解释每一行代码 - 但如果您仍有问题，我很乐意为您解答！
此外，如果您重新构造代码，您可以轻松地允许从类外部更改毕业角度以及其他变量。我在下面的完整项目中提供了一个示例。