swift - 如何在 Swift 3 中画一条线

Question

我希望用户触摸 2 个点，然后在这两点之间画一条线。这是我目前所拥有的:

func drawline(){
    let context = UIGraphicsGetCurrentContext()
    context!.beginPath()
    context?.move(to: pointA)
    context?.addLine(to: pointB)
    context!.strokePath()
}

pointA 是用户触摸的第一个点，pointB 是第二个点。我收到错误:

thread 1:EXC_BREAKPOINT

预先感谢您的帮助。

Answer 1

要在两点之间画一条线，您需要做的第一件事是从当前 UIView 获取 CGPoints，有几种方法可以实现这一点。为了示例的缘故，我将使用 UITapGestureRecognizer 来检测您何时进行点击。

另一个步骤是，一旦你保存了两个点，就在两点之间绘制线，为此，你可以像以前一样使用图形上下文或使用 CAShapeLayer。

所以翻译上面的解释我们得到以下代码:

class ViewController: UIViewController {

   var tapGestureRecognizer: UITapGestureRecognizer!

   var firstPoint: CGPoint?
   var secondPoint: CGPoint?

   override func viewDidLoad() {
       super.viewDidLoad()

       tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(self.showMoreActions(touch:)))
       tapGestureRecognizer.numberOfTapsRequired = 1
       view.addGestureRecognizer(tapGestureRecognizer)
   }

   func showMoreActions(touch: UITapGestureRecognizer) {
       let touchPoint = touch.location(in: self.view)

       guard let _ = firstPoint else {
           firstPoint = touchPoint
           return
       }

       guard let _  = secondPoint else {
           secondPoint = touchPoint
           addLine(fromPoint: firstPoint!, toPoint: secondPoint!)

           firstPoint = nil
           secondPoint = nil

           return
       }
   }

   func addLine(fromPoint start: CGPoint, toPoint end:CGPoint) {
       let line = CAShapeLayer()
       let linePath = UIBezierPath()
       linePath.move(to: start)
       linePath.addLine(to: end)
       line.path = linePath.cgPath
       line.strokeColor = UIColor.red.cgColor
       line.lineWidth = 1
       line.lineJoin = kCALineJoinRound
       self.view.layer.addSublayer(line)
   }
}

上面的代码是每选中两个点就画一条线，你可以根据需要自定义上面的函数。

希望对你有帮助