Image Literals, Arrays and randomizing in Swift. Why does this method work but the other doesn't - Ios swift

Beshoy
October 9, 2022
193 views
0 votes
2 Answers

Creating a dice roll app following Angela Yu’s App Brewery bootcamp on Udemy. She uses image literals but those seem to have been deprecated on newer versions of Xcode.

I get the error: Cannot assign value of type ‘UIImage??’ to type ‘UIImage?’ Whenever I try to use diceArray.randomElement()

However, diceArray[Int.random(in:0...5] seems to work fine. My suspicion is maybe to use .randomElement() I need to use imageView but new to Swift so not sure if this is correct or what the difference even is. Any explanation would be appreciated. Thanks.

      @IBAction func rollButtonPressed(_ sender: UIButton) {
            
            
           var diceArray = [UIImage(named: "DiceOne"),UIImage(named: "DiceTwo"),UIImage(named: "DiceThree"),UIImage(named:"DiceFour"),UIImage(named:"DiceFive"),UIImage(named:"DiceSix")]
           
            diceImageView1.image = diceArray.randomElement()
            diceImageView2.image = diceArray[Int.random(in: 0...5)]
          
            
        }

Answers

- ShehataGamal
- October 9, 2022 at 12:48 am
- 0 votes
0
UIImage(named: initializer returns UIImage? and randomElement returns an Optional so it’s ?? , you can force it
```
diceImageView1.image = diceArray.randomElement()!
```
Login or Signup to reply.

- DuncanC
- October 9, 2022 at 1:19 am
- 0 votes
0
As Sh_Khan pointed out, you have an array of Optionals since UIImage.named(_:) returns an Optional.

I would suggest adding a call to compactMap at the end of your code that declares your array of images:
```
var diceArray = [UIImage(named: "DiceOne")…].compactMap { $0 }
```
That will make diceArray an array of UIImages instead of Optional(UIImage) (and strip out any failed attempts to load images.)

Edit:

Alexander pointed out in the comments that this might be a case where force-unwrapping is a good thing.

If you write the code like this:
```
var diceArray = [
    UIImage(named: "DiceOne")!,
    UIImage(named: "DiceTwo")!,
    UIImage(named: "DiceThree")!,    
    UIImage(named:"DiceFour")!,    
    UIImage(named:"DiceFive")!,
    UIImage(named:"DiceSix")!
]
```
That version will also create an array of non-optional UIImages. If you mis-name any of the images, or there are other problems, the above code will crash immediately. Once it runs without crashing, though, you can be confident that the images will continue to load.

The version with compactMap() would simply create an array when any misnamed images were missing.
Login or Signup to reply.