与Android类似,绘制过程需要重写draw(_ rect:CGRect)方法

class CustomUIView:UIView{
  override func draw(_ rect:CGRect){
    //上下文对象:可以理解为具体的设备对象，比如IOS设备，MacOS设备，PDF等
    let context = UIGraphicsGetCurrentContext()
    //设置线段属性
    setLineProperties(context)
    //绘制直线
    drawLine(context)
    //绘制虚线
    drawDashLine(context)
    //绘制椭圆
    drawEllipse(context)
    //绘制圆形
    drawCircle(context)
    //绘制弧线
    drawArc(context)
    //绘制矩形
    drawRect(context)
    //绘制路径
    drawPath(context)
    //裁剪区域
    clipArea(context)
  }
}

绘制方法

extension CustomUIView{

  private func setLineProperties(_ context:CGContext?){
        //设置线段相关属性
        context?.setLineJoin(.round)
        context?.setStrokeColor(UIColor.red.cgColor)
        context?.setLineWidth(2)
        context?.setLineCap(CGLineCap.square)
   }

  private func drawLine(_ context:CGContext?){
        //将起始点移动到原点
        context?.move(to: CGPoint(x: 0, y: 0))
        //此函数以当前点为startPoint，连接线段到终点(endPoint)
        context?.addLine(to: CGPoint(x: 50, y: 50))
        //调用这个函数才能真正绘制出线段
        context?.strokePath()
   }

  private func drawArc(_ context:CGContext?){
        //参数分别为:center(圆心),radius(半径),startAngle(开始角度:以弧度表示),endAngle(结束角度:以弧度表示),clockwise(true为顺时针圆弧,false为逆时针圆弧)
        let center = CGPoint(x: bounds.width/2, y: bounds.height/2)
        let radius = bounds.width/2
        let startAngle = CGFloat(90).asRad()
        let endAngle = CGFloat(180).asRad()
        print("endAngle = \(endAngle)")
        let clockwise = false
        context?.addArc(center: center, radius: radius, startAngle: startAngle, endAngle: endAngle, clockwise: clockwise)
        context?.strokePath()
   }

    private func drawRect(_ context:CGContext?){
        let rect = CGRect(x: 70, y: 50, width: 100, height: 50)
        context?.addRect(rect)
        context?.strokePath()
    }
}

因为drawArc参数是弧度，所以这里扩展一下CGFloat方法，支持弧度输出

extension CGFloat{
    //转成弧度
    func asRad() -> CGFloat{
        return self * CGFloat.pi / 180
    }
}

触摸手势处理

//MARK:重写触摸拦截
extension CustomUIView{
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        print("touchesBegan")
    }
    
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        print("touchesMoved")
    }
    
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        print("touchesEnded")
    }
    
    override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
        print("touchesCancelled")
    }
    
}