swift - 如何在swift 3中的图像上的两点之间画一条线？

Question

我是 swift 新手，我想在我称为 mapView 的图像上的 2 点之间画一条线，我尝试使用 CGContext 但没有结果，有什么帮助吗？谢谢。

UIGraphicsBeginImageContext(mapView.bounds.size)
    let context : CGContext = UIGraphicsGetCurrentContext()!
    context.addLines(between: [CGPoint(x:oldX,y:oldY), CGPoint(x:newX, y:newY)])
    context.setStrokeColorSpace(CGColorSpaceCreateDeviceRGB())
    context.setStrokeColor(UIColor.blue.cgColor.components!)
    context.setLineWidth(3)
    mapView?.image?.draw(at: CGPoint(x:0, y:0))
    context.strokePath()
    mapView.image = UIGraphicsGetImageFromCurrentImageContext()!
    UIGraphicsEndImageContext()

Answer 1

一种选择是将子视图添加到您的图像视图并将线条绘制代码添加到其draw(_ rect: CGRect)方法中。

一个示例游乐场实现：

class LineView : UIView {
    override init(frame: CGRect) {
        super.init(frame: frame)
        self.backgroundColor = UIColor.init(white: 0.0, alpha: 0.0)
    }

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

    override func draw(_ rect: CGRect) {
        if let context = UIGraphicsGetCurrentContext() {
            context.setStrokeColor(UIColor.blue.cgColor)
            context.setLineWidth(3)
            context.beginPath()
            context.move(to: CGPoint(x: 5.0, y: 5.0)) // This would be oldX, oldY
            context.addLine(to: CGPoint(x: 50.0, y: 50.0)) // This would be newX, newY
            context.strokePath()
        }
    }
}


let imageView = UIImageView(image: #imageLiteral(resourceName: "image.png")) // This would be your mapView, here I am just using a random image
let lineView = LineView(frame: imageView.frame)
imageView.addSubview(lineView)