如何在Swift 3中画一条线 [英] How to draw a line in Swift 3

问题描述

我希望用户触摸2点，然后在这两点之间画一条线。这是我到目前为止的内容：

I would like the user to touch 2 points and then a line is drawn between those two points. Here is what I have so far:

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

pointA 是用户触摸的第一点，并且 pointB 是第二点。我收到错误消息：

pointA is the first point the user touched and pointB is the second point. I get the error:

thread 1:EXC_BREAKPOINT

在此先感谢您的帮助。

推荐答案

在两条线之间画一条线要点，首先需要从当前的 UIView 获取 CGPoints ，有几种方法可以实现。为了示例，我将使用 UITapGestureRecognizer 来检测您何时点击。

To draw a line between two points the first thing you need is get the CGPoints from the current UIView, there are several ways of achieve this. I going to use an UITapGestureRecognizer for the sake of the sample to detect when you make a tap.

步骤是，一旦保存了两个点，就在两个点之间绘制了一条线，然后可以再次使用图形上下文，或者使用 CAShapeLayer 。

The another step is once you have the two points saved draw the line between the two points, and for this again you can use the graphics context as you try before or use CAShapeLayer.

因此，通过翻译上面的解释，我们得到以下代码：

So translating the explained above we get the following code:

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)
   }
}

上面的代码将在每次选择两个点时画一条线，您可以根据需要自定义上面的函数。

The above code is going to draw a line every time two points are selected and you can customize the above function as you like.

希望对您有所帮助。

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