实现原理

1、使用拖动手势记录获取用户签名路径.
2、当用户初次接触屏幕,生成一个新的UIBezierPath,并加入数组中.设置接触点为起点.在手指拖动过程中为UIBezierPath添加线条,并重新绘制,生成连续的线.
3、手指滑动中不断的重新绘制,形成签名效果.
4、签名完成,转化为UIImage保存.

class CXGSignView: UIView {

 var path: UIBezierPath?
 var pathArray: [UIBezierPath] = []

 override init(frame: CGRect) {
 super.init(frame: frame)
 self.backgroundColor = UIColor.gray
 setupSubviews()
 }


 required init?(coder aDecoder: NSCoder) {
 fatalError("init(coder:) has not been implemented")
 }


 func setupSubviews() {

 let panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(panGestureRecognizerAction(_:)))
 self.addGestureRecognizer(panGestureRecognizer)

 }

 @objc func panGestureRecognizerAction(_ sender: UIPanGestureRecognizer) {
 // 获取当前点
 let currentPoint = sender.location(in: self)

 if sender.state == .began {
  self.path = UIBezierPath()
  path?.lineWidth = 2
  path?.move(to: currentPoint)
  pathArray.append(path!)
 }else if sender.state == .changed {
  path?.addLine(to: currentPoint)
 }
 self.setNeedsDisplay()
 }

 // 根据 UIBezierPath 重新绘制
 override func draw(_ rect: CGRect) {

 for path in pathArray {
  // 签名颜色
  UIColor.black.set()
  path.stroke()
 }
 }

 // 清空
 func clearSign() {
 pathArray.removeAll()
 self.setNeedsDisplay()
 }

 // 撤销
 func undoSign() {
 guard pathArray.count > 0 else {
 return
 }
 pathArray.removeLast()
 self.setNeedsDisplay()
 }

 /// 签名转化为图片
 func saveSignToImage() -> UIImage? {
 UIGraphicsBeginImageContextWithOptions(self.bounds.size, false, UIScreen.main.scale)
 guard let context = UIGraphicsGetCurrentContext() else {
  return nil
 }
 self.layer.render(in: context)
 let image = UIGraphicsGetImageFromCurrentImageContext()
 UIGraphicsEndImageContext()
 return image
 }
}