关于线程 1：致命错误：在隐式展开可选值时意外发现 nil [重复]

Question

我有一个线程 1：致命错误：在我的项目中隐式展开可选值错误时意外发现 nil 我托盘很多，但我无法修复它。任何人都可以帮助我。 enter image description here 这是代码： 我认为问题出在类（画布）上，因为当我调用视图时这将是一个问题，但我的应用程序需要这样做。

    import UIKit
import Foundation
class WarmUpControlClass: UIViewController {

    @IBOutlet weak var UserImage: UIImageView!
    let canvas = WarmUp()
    //func to creates and instantiates the UIView object (warmUp class object)
   override func loadView() {
 //to call functions in the warm up class to enable user drawing

   self.view = canvas

    }
    override func viewDidLoad() {
         //to show the user image in the top right corner

              let decodedData = Data(base64Encoded: SelectedUser.ImageString, options: .ignoreUnknownCharacters)
              let decodedimage:UIImage? = UIImage(data: decodedData! as Data)
              UserImage.image = decodedimage //i put .image to convert from UIimage to UIimageVeiw
              UserImage.image = decodedimage
              UserImage.layer.cornerRadius = UserImage.frame.size.width/2
              UserImage.clipsToBounds = true


        canvas.backgroundColor = .white //to set white background to drawing screen
        super.viewDidLoad()
}//end conterol class
    //this class to do all drawing methods (user writing)
    class WarmUp: UIView {



        override func draw(_ rect: CGRect) {
               super.draw(rect)  //custom drawing
               guard let context = UIGraphicsGetCurrentContext() else
               { return }
            context.setStrokeColor(UIColor.gray.cgColor)
               context.setLineWidth(8)
               context.setLineCap(.round)
               lines.forEach { (line) in
                       for(i , p) in line.enumerated(){
                           if i == 0 {
                           context.move(to: p)
                           } else {
                           context.addLine(to: p)
                           }
                       }//end for
                    }
               context.strokePath()
           }
           var lines = [[CGPoint]]()//two dimantional array
           override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
               lines.append([CGPoint]())
           }
           //track the finger as we move across screen
           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()
           }

    }

}

有人帮忙吗？

Answer 1

DecodedImage 为零。你应该检查一下，为什么它是 nil。

最好询问一个可选项是否为 nil，例如

If let image = imageOptional {
// in here image is not optional
} else {
// maybe print error here
}