ios - 不确定如何为现有代码正确设置我的变量。 fatal error : Unexpectedly found nil while implicitly unwrapping an Optional value

Question

我目前正在尝试从 viewcontrollers viewdidload() 中的单独类运行一个函数。以前的开发人员团队编写了代码，我正在努力让它工作，因为我对 swift 也很陌生。

我没有包含所有函数，因为它很长，但只是想知道我是否可以得到一些建议，我收到错误“ fatal error :意外发现 nil 同时隐式展开可选值”对于 shapelayer 值，我知道是因为它们还没有被初始化，但我正在努力弄清楚如何正确设置变量而不弄乱整个代码，只是希望得到一些指导。

我确定我可能需要解释更多，但是有很多代码，我整天都在盯着它，如果我需要再上传，请告诉我。

class TraceViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {

  @IBOutlet weak var canvasView: CanvasView!
  static var curLetter = "A"

  override func viewDidLoad() {
    canvasView.letter = TraceViewController.curLetter
    canvasView.clearCanvas()
  }
}

类(class):

class CanvasView:UIView { 
  var lineColour:UIColor!
  var lineWidth:CGFloat!
  var path:UIBezierPath!
  var touchPoint:CGPoint!
  var startingPoint:CGPoint!

  var initialPoint:CGPoint!

  var stroke1Done = false
  var stroke2Done = false
  var stroke3Done = false
  var stroke4Done = false
  var stroke5Done = false
  var stroke6Done = false
  var stroke7Done = false

 //Track current stroke and add all the shape layers into an array
  var currentStroke = 1
  var strokesArray = [CAShapeLayer]()

func drawShapeLayer() {
    let shapeLayer = CAShapeLayer()
    shapeLayer.path = path.cgPath //error here
    shapeLayer.strokeColor = lineColour.cgColor
    shapeLayer.lineWidth = lineWidth
    shapeLayer.fillColor = UIColor.clear.cgColor
    self.layer.addSublayer(shapeLayer)

    //Add the shapes in array so that we can track it
    self.strokesArray.append(shapeLayer)

    self.setNeedsLayout()
}

func clearCanvas() {
    guard path != nil else {return}
    path.removeAllPoints()
    self.layer.sublayers = nil
    self.setNeedsDisplay()
    print("Hello")
    stroke1Done = false
    stroke2Done = false
    stroke3Done = false
    stroke4Done = false
    stroke5Done = false
    stroke6Done = false
    stroke7Done = false

    goNext = false

    updateStrokePoints()

    updateStrokeDifference()

    currentStroke = 1
 }
}

Answer 1

该错误似乎是因为您在使用它之前没有设置路径。您需要设置 path在实际调用它之前。

第一的:

var path: UIBezierPath?

然后:

path = UIBezierPath()

最后，使用它:

shapeLayer.path = path?.cgPath

另外，记得使用 ?而不是 !强制展开总是不好的做法。