用Swift 3.0实时绘制一条线

我试图画一个UIImageView。 随着Swift 1.2，我能够得到它的工作，但我不得不将其转换为3.0，我不能得到它的工作。

它需要做的就是用你的手指画出你在屏幕上画的东西。

代码没有提供任何错误，只是不显示任何内容。

variables;

var lastPoint = CGPoint.zero var red: CGFloat = 0.0 var green: CGFloat = 0.0 var blue: CGFloat = 0.0 var brushWidth: CGFloat = 10.0 var opacity: CGFloat = 1.0 var swiped = false 

代码;

 override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) { swiped = false if let touch = touches.first { lastPoint = touch.location(in: self.view) } } func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint) { imageView.image?.draw(in: CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height)) UIGraphicsBeginImageContext(self.imageView.bounds.size); let context = UIGraphicsGetCurrentContext() context?.move(to: fromPoint) context?.addLine(to: toPoint) context?.setLineCap(CGLineCap.round) context?.setLineWidth(brushWidth) context?.setStrokeColor(red: red, green: green, blue: blue, alpha: 1.0) context?.setBlendMode(CGBlendMode.normal) imageView.image = UIGraphicsGetImageFromCurrentImageContext() imageView.alpha = opacity UIGraphicsEndImageContext() } override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) { swiped = true if let touch = touches.first { let currentPoint = touch.location(in: view) drawLineFrom(fromPoint: lastPoint, toPoint: currentPoint) lastPoint = currentPoint } } override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) { if !swiped { // draw a single point self.drawLineFrom(fromPoint: lastPoint, toPoint: lastPoint) } 

Answer 1

您必须开始图像上下文：

 UIGraphicsBeginImageContextWithOptions(view.bounds.size, false, 0) 

你也必须打破这个道路：

 context?.strokePath() 

你也没有画出前一个图像：

 imageView.image?.draw(in: view.bounds) 

从而：

 func drawLine(from fromPoint: CGPoint, to toPoint: CGPoint) { UIGraphicsBeginImageContextWithOptions(view.bounds.size, false, 0) imageView.image?.draw(in: view.bounds) let context = UIGraphicsGetCurrentContext() context?.move(to: fromPoint) context?.addLine(to: toPoint) context?.setLineCap(CGLineCap.round) context?.setLineWidth(brushWidth) context?.setStrokeColor(red: red, green: green, blue: blue, alpha: 1.0) context?.setBlendMode(CGBlendMode.normal) context?.strokePath() imageView.image = UIGraphicsGetImageFromCurrentImageContext() imageView.alpha = opacity UIGraphicsEndImageContext() }