当我尝试使用userDefaults保存为ui颜色时，Xcode给我以下错误：致命错误：在展开可选值时意外发现nil

Question

I am trying to allow my app to save UIColors in settings, and when I tried to save the settings for the background color it worked. But when I add a second block of code that should allow me to save a second UIColor, it gives me the error - Fatal error: Unexpectedly found nil while unwrapping an Optional value. Can someone show me how to save the second UIColor without an error?

      // First UIColor save - Works
    var dd = UIColor(hex: UserDefaults.standard.value(forKey: "TheMainUIColour") as! String )

    UserDefaults.standard.set(dd.toHexString, forKey: "TheMainUIColour")

    let  mainBackgroundColour = UserDefaults.standard.value(forKey: "TheMainUIColour") as! String

    let color = UIColor(hex: mainBackgroundColour)

    self.view.backgroundColor = dd

    // Second UIColor Save - Doesnt Work
    let dd2: UIColor = UIColor(hex: UserDefaults.standard.value(forKey: "TheMainUIColour2") as! String )
    UserDefaults.standard.set(dd2, forKey: "TheMainUIColour2")

    let  mainBackgroundColour2 = UserDefaults.standard.value(forKey: "TheMainUIColour2") as! String

    let color2 = UIColor(hex: mainBackgroundColour2)

Answer 1

The problem is

   var dd2:UIColor = UIColor(hex: UserDefaults.standard.value(forKey: "TheMainUIColour2") as! String )

it reads from defaults not save , don't use ! to read from defaults as the stored value may be nil , jsut use if let to check the existence of it in defaults or not , if exists use it , if not save the value you want , wjen you open the app again it will read that stored value

   if let saved = UserDefaults.standard.string(forKey: "TheMainUIColour2") 
   {
       var dd = UIColor(hex:saved)
   }
   else
   {
        print("No saved color")

        let dd = UIColor.red

        UserDefaults.standard.set(dd.toHexString, forKey: "TheMainUIColour2")

   }

Answer 2

Your code crashes because there is nothing set for the key TheMainUIColour2 but you then force-unwrap that nil value and your app crashes.

Your code also makes little sense as written. You (attempt to) load the current value and create a color from it. You then needlessly write that value back to user defaults. Then you read the value again as a string. And then you create the color from the string again.

Don't do all of those needless extra steps. Load the color if it exists and that is it. This code should not be setting anything. You must have other code that decides on what color to use. That code should save the color to user defaults.

if let hexColor = UserDefaults.standard.string(forKey: "TheMainUIColour2") {
    let color2 = UIColor(hex: hexColor)
    // do something with the color
}