如何将图像放在 uiview 绘图之上（swift5）答案

【问题标题】：how to place image on top of uiview drawing (swift5)如何将图像放在 uiview 绘图之上（swift5）
【发布时间】：2019-05-26 18:05:26
【问题描述】：

我下面的代码将 a 放在绘图区域的后面。因此，如下图所示。我画的任何东西都在线条的前面。我想让我画的任何东西都在线条后面。我的所有代码都附在下面。图片也在 assets 文件夹中。

class ViewController: UIViewController {
    var editBtn = UIButton()
    var canVasView = UIView()
    var path = UIBezierPath()
    var startPoint = CGPoint()
    var touchPoint = CGPoint()

    func addArrowImageToButton(button: UIButton, arrowImage:UIImage = #imageLiteral(resourceName: "graph.png") ) {
        let btnSize:CGFloat = 32
        let imageView = UIImageView(image: arrowImage)
        let btnFrame = button.frame

        button.bringSubviewToFront(imageView)
    }

    override func viewDidAppear(_ animated: Bool) {
        self.addArrowImageToButton(button: editBtn)
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        setup()
        draw()
        view.addSubview(editBtn)
        view.addSubview(canVasView)

        editBtn.backgroundColor = UIColor.orange
        canVasView.backgroundColor = UIColor.purple

        editBtn.translatesAutoresizingMaskIntoConstraints = false
        canVasView.translatesAutoresizingMaskIntoConstraints = false

        let myLayer = CALayer()
        let myImage = UIImage(named: "graph.png")?.cgImage
        myLayer.frame = CGRect(x: 40, y: -80, width: 300, height: 300)
        myLayer.contents = myImage
        canVasView.layer.addSublayer(myLayer)

        self.view.addSubview(canVasView)

        NSLayoutConstraint.activate ([
            canVasView.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :175),
            canVasView.topAnchor.constraint(equalTo: view.centerYAnchor, constant : 100),
            canVasView.widthAnchor.constraint(equalToConstant: 350),
            canVasView.heightAnchor.constraint(equalToConstant: 180),

            editBtn.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :175),
            editBtn.topAnchor.constraint(equalTo: view.centerYAnchor, constant : 0),
            editBtn.widthAnchor.constraint(equalToConstant: 350),
            editBtn.heightAnchor.constraint(equalToConstant: 180),
        ])

        editBtn.addTarget(self, action: #selector(didTapEditButton), for: .touchUpInside)
    }

    @objc func didTapEditButton() {
        path.removeAllPoints()
        canVasView.layer.sublayers = nil
        canVasView.setNeedsDisplay()

        self.addArrowImageToButton(button: editBtn)
    }

    func setup(){
        editBtn.layer.cornerRadius = 20
        canVasView.clipsToBounds = true
        canVasView.isMultipleTouchEnabled = false
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        let touch = touches.first
        if let point = touch?.location(in: canVasView){
            startPoint = point
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        let touch = touches.first
        if let point = touch?.location(in: canVasView){
            touchPoint = point
        }

        path.move(to: startPoint)
        path.addLine(to: touchPoint)
        startPoint = touchPoint
        draw()
    }

    func draw() {
        let strokeLayer = CAShapeLayer()
        strokeLayer.fillColor = nil
        strokeLayer.lineWidth = 5
        strokeLayer.strokeColor = UIColor.blue.cgColor
        strokeLayer.path = path.cgPath
        canVasView.layer.addSublayer(strokeLayer)
        canVasView.setNeedsDisplay()
    }
}

【问题讨论】：

标签： swift uiview draw uibezierpath cgpoint

【解决方案1】：

要在线条图像后面绘制，您需要在其后面添加笔触图层。为此，请在 viewDidLoad 之外声明 myLayer，然后将绘制函数更改为：

func draw() {
    let strokeLayer = CAShapeLayer()
    strokeLayer.fillColor = nil
    strokeLayer.lineWidth = 5
    strokeLayer.strokeColor = UIColor.blue.cgColor
    strokeLayer.path = path.cgPath
    canVasView.layer.insertSublayer(strokeLayer, below: myLayer) //draw behind myLayer
    canVasView.setNeedsDisplay()
}

【讨论】：