swift - SetNeedsDisplay 无效

Question

我正在 UIContainerView 中创建 subview ，它属于下面描述的类。这些值正确地打印到终端窗口，但实际上并没有显示在我定义的 subview 中。我认为 setNeedsDisplay() 应该解决这个问题，但什么也没有出现。

我将此 subview 创建为 let canvas = Canvas() 并尝试了

canvas.setNeedsDisplay() 无效。

class Canvas: UIView {

  override func draw(_ rect: CGRect) {

      super.draw(rect)
      guard let context = UIGraphicsGetCurrentContext() else { return }

      context.setStrokeColor(login_theme_color.cgColor)
      context.setLineWidth(10.0)
      context.setLineCap(.butt)

      lines.forEach { (line) in
      for(i, p) in line.enumerated(){
          //context.move(to: p)
          //context.addLine(to: p)
          if i == 0 {
              context.move(to: p)
              print("First point of new line is \(p)")
          }else{
              context.addLine(to: p)
              print("point is \(p)")
          }
      }
  }
       context.strokePath()
}

  var lines = [[CGPoint]]()

  override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
      lines.append([CGPoint]())
      //setNeedsDisplay()
  }
  override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
      guard let point = touches.first?.location(in: nil) else { return }
      guard var lastLine = lines.popLast() else { return }
      lastLine.append(point)
      lines.append(lastLine)
      setNeedsDisplay()
  }

}

为什么值会正确地打印到终端，但行数组实际上并没有在 View 中显示值？非常感谢您的帮助。

我使用以下约束定义我的 Canvas :

    let canvas = Canvas()

    @objc fileprivate func setupCanvas(){
        //canvas.setNeedsDisplay()
        containerView.addSubview(canvas)
        canvas.translatesAutoresizingMaskIntoConstraints = false
        canvas.topAnchor.constraint(equalTo: rectangle2.topAnchor, constant: 74).isActive = true
        canvas.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor, constant: (view.frame.width/2) + 8).isActive = true
        canvas.rightAnchor.constraint(equalTo: rectangle2.rightAnchor, constant: -4).isActive = true
        canvas.bottomAnchor.constraint(equalTo: howitWorksText.bottomAnchor, constant: 0).isActive = true
        canvas.layer.cornerRadius = 30
        canvas.layer.shadowRadius = 0.5
        canvas.layer.shadowColor = UIColor.white.cgColor
        //canvas.backgroundColor = UIColor.clear
        //canvas.layer.borderWidth = 2.0
        //canvas.layer.borderColor = UIColor.black.cgColor
        canvas.layer.masksToBounds = true
        canvas.backgroundColor = .white
        //canvas.setNeedsDisplay()
    }

并在我的 ViewDidLoad() 中调用 setupCanvas()

Answer 1

您的坐标不对，因为您使用了错误的引用系。为 location(in view:) 中的 View 指定 nil选择窗口的坐标空间。因此，即使您的触摸在 Canvas 内，您的绘图却不在。您想通过将 self 而不是 nil 传递给 location(in:) 来获取 Canvas View 内部的触摸坐标。

在 touchesMoved() 中更改:

guard let point = touches.first?.location(in: nil) else { return }

到:

guard let point = touches.first?.location(in: self) else { return }

---

有关更多信息，请查看 location(in:) 的文档.