Ios 如何在ScrollView中的图像上绘制线条-Swift 3

我正在创建一个应用程序，允许用户在包含在滚动视图中的图像上绘制两个矩形。然而，目前这条线似乎还没有画出来

以下是处理图形的UIViewController：

import UIKit
import CoreGraphics
import CoreData

class PhotoZoomController: UIViewController {

    //Photo View's Variables
    @IBOutlet weak var scrollView: UIScrollView!

    @IBOutlet weak var photoImageView: UIImageView!
    @IBOutlet weak var imageViewLeadingConstraint: NSLayoutConstraint!
    @IBOutlet weak var imageViewBottomConstraint: NSLayoutConstraint!
    @IBOutlet weak var imageViewTopConstraint: NSLayoutConstraint!
    @IBOutlet weak var imageViewTrailingConstraint: NSLayoutConstraint!

    var photo: Photo!

    var indicatorPoints: [CGPoint]!
    var objectPoints: [CGPoint]!

    var context: NSManagedObjectContext!

    var brushWidth: CGFloat = 10.0;
    var brushColor: CGColor = UIColor.cyan.cgColor

    override func viewDidLoad() {
        super.viewDidLoad()

        photoImageView.image = photo.image
        photoImageView.sizeToFit()
        scrollView.contentSize = photoImageView.bounds.size
        updateZoomScale()
        updateConstraintsForSize(view.bounds.size)
        view.backgroundColor = .black        
    }

    var minZoomScale: CGFloat {
        let viewSize = view.bounds.size
        let widthScale = viewSize.width/photoImageView.bounds.width
        let heightScale = viewSize.height/photoImageView.bounds.height

        return min(widthScale, heightScale)
    }

    func updateZoomScale() {
        scrollView.minimumZoomScale = minZoomScale
        scrollView.zoomScale = minZoomScale
    }

    func updateConstraintsForSize(_ size: CGSize) {
        let verticalSpace = size.height - photoImageView.frame.height
        let yOffset = max(0, verticalSpace/2)
        imageViewTopConstraint.constant = yOffset
        imageViewBottomConstraint.constant = yOffset

        let xOffset = max(0, (size.width - photoImageView.frame.width)/2)
        imageViewLeadingConstraint.constant = xOffset
        imageViewTrailingConstraint.constant = xOffset
    }


    @IBAction func tappedInside(_ sender: Any) {
        guard let sender = sender as? UITapGestureRecognizer else {
            return
        }

        let touch = sender.location(in: self.photoImageView)

        for i in 0...3 {
            if indicatorPoints[i] == CGPoint() {
                indicatorPoints[i] = touch
                return
            }
        }

        for i in 0...3 {
            if objectPoints[i] == CGPoint() {
                objectPoints[i] = touch
                return
            }
        }

    //This part isn't finished, but it's supposed to modify previous points

    }
}


extension PhotoZoomController {

我觉得这就是我的问题开始的地方。我知道这段代码在运行，因为我在这里放了一个print语句，它就运行了

    func drawLine(between points: [CGPoint]) {
        UIGraphicsBeginImageContextWithOptions(self.photoImageView.bounds.size, false, 0)

        photoImageView.image?.draw(in: self.photoImageView.bounds)

        guard let context = UIGraphicsGetCurrentContext() else {
            return
        }

        context.setLineCap(.round)
        context.setLineWidth(brushWidth)
        context.setStrokeColor(brushColor)
        context.addLines(between: points)
        context.strokePath()

        UIGraphicsEndImageContext()
    }
}

extension PhotoZoomController: UIScrollViewDelegate {
    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return photoImageView
    }

    func scrollViewDidZoom(_ scrollView: UIScrollView) {
        updateConstraintsForSize(view.bounds.size)

        if scrollView.zoomScale < minZoomScale {
            dismiss(animated: true, completion: nil)
        }
    }
}

func绘制线（点之间：[CGPoint]）{
UIGraphicsBeginImageContextWithOptions（self.photoImageView.bounds.size，false，0）
photoImageView.image？绘图（在：self.photoImageView.bounds中）
guard let context=UIGraphicsGetCurrentContext（）else{
回来
}
context.setLineCap（.round）
context.setLineWidth（笔刷宽度）
context.setStrokeColor（brushColor）
context.addLines（在：点之间）
context.strokePath（）
UIGraphicsSendImageContext（）
}
}
扩展PhotoZoomController:UIScrollViewDelegate{
func VIEWFOR缩放（在scrollView:UIScrollView中）->UIView{
返回照片视图
}
func scrollViewDidZoom（scrollView:UIScrollView）{
updateConstraintsForSize（view.bounds.size）
如果scrollView.zoomScale

这就是UIViewController当前的外观（可能视图顺序有问题？） 你是说

UIGraphicsBeginImageContextWithOptions

及

在它们之间，当上下文存在时，你就进入其中

到目前为止，一切顺利

但你说什么都没有

UIGraphicsGetImageFromCurrentImageContext

因此，包含绘图结果的上下文将被丢弃

UIGraphicsGetImageFromCurrentImageContext