fixing - Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

I am new to coding and have been trying to make an area on the screen that I can sign with my finger. I have made the box but I am struggling to clear it. I have made a button connected to a function to clear the path but I can't seem to work out how to safely unwrap the information without it crashing.

import UIKit

class canvasView: UIView {

    var lineColour:UIColor!
    var lineWidth:CGFloat!
    var path:UIBezierPath!
    var touchPoint:CGPoint!
    var startingPoint:CGPoint!


    override func layoutSubviews() {
        self.clipsToBounds = true
        self.isMultipleTouchEnabled = false

        lineColour = UIColor.white
        lineWidth = 10
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        let touch = touches.first
        startingPoint = (touch?.location(in: self))!
    }

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

        path = UIBezierPath()
        path.move(to: startingPoint)
        path.addLine(to: touchPoint)
        startingPoint = touchPoint

        drawShapelayer()
    }
    func drawShapelayer(){
        let shapeLayer = CAShapeLayer()
        shapeLayer.path = path.cgPath
        shapeLayer.strokeColor = lineColour.cgColor
        shapeLayer.lineWidth = lineWidth
        shapeLayer.fillColor = UIColor.clear.cgColor
        self.layer.addSublayer(shapeLayer)
        self.setNeedsDisplay()
    }

    func clearCanvas() {
        path.removeAllPoints()
        self.layer.sublayers = nil
        self.setNeedsDisplay()
    }

I then get the error in my final function after

path.removeAllPoints()

How is best to unwrap it to stop it crashing?

Thank you for your patience

The problem is that if the user clicks the button to clear the canvas before he/she draws anything, then the error will occur, since path is only assigned a value in touchesMoved().

You might want to change

var path:UIBezierPath!

to

var path:UIBezierPath?

Though this may seem tedious since you have to add question marks everywhere you try to access a method or property of path, it's much safer, and the code in your example will not crash.

P.S. Check out this answer. It provides a lot of information regarding the use of optionals.