Randomly generated array works only on buttons

Question

I've tried a lot of approaches to randomly generate an array from existing one. And one of them finally worked out for me:

    extension Array {
    mutating func shuffle() {
// get data from my FireBase and calculate amount of items in it
        var ref: DatabaseReference?
        var databaseHandle: DatabaseHandle?
        var words = [lWord]()
        ref = Database.database().reference()
            guard let uid = Auth.auth().currentUser?.uid else {
                print ("smt wrong with user uid")
                return
            }
           databaseHandle = ref?.child("Users").child(uid).child("LearningNow").observe(.value, with: { (snapshot) in
                var newItems: [lWord] = []
                for item in snapshot.children {
                    let wordItem = lWord(snapshot: item as! DataSnapshot)
                    newItems.append(wordItem)
                }
                words = newItems
            })
        let count = words.count + 1
        for _ in 0..<count  {
            sort { (_,_) in arc4random() < arc4random() }
        }
    }
}

But, for some reasons, this code works only if I put this method on the array inside of the button-action, for example:

@IBAction func generate(_ sender: UIButton) {
    words.shuffle()
    print (words)
}

If put exactly the same code in the viewDidLoad, nothing is sorted. So how can I sort my array without any action?

P.S. If you don't know the answer, you can recommend any other approach to generate random array. Thank You!

The most likely problem is that the changes performed in `viewDidLoad` get written over by code that executes later. See if putting the same code into `viewWillAppear` fixes the problem. — Sergey Kalinichenko, Aug 05 '17 at 19:23
No, it also doesn't work. Maybe the problem is that I retrieve the same data from FireBase twice? The first time in the ViewDidLoad, and the second in the extension, otherwise I don't know how to constraint for loop there, because the number of items in the array can be different . — Oleg Blanutsa, Aug 05 '17 at 19:40
Try putting the `for _ in` loop inside the `.observe`'s completion handler, right below `words = newItems` — RPatel99, Aug 05 '17 at 21:04

score 0 · Answer 1 · answered Aug 06 '17 at 16:12

Thank you for all your replies! I found the solution, I had to replace my method (code is from this question):

extension Array {
/// Returns an array containing this sequence shuffled
var shuffled: Array {
    var elements = self
    return elements.shuffle()
}
/// Shuffles this sequence in place
@discardableResult
mutating func shuffle() -> Array {
    indices.dropLast().forEach {
        guard case let index = Int(arc4random_uniform(UInt32(count - $0))) + $0, index != $0 else { return }
        swap(&self[$0], &self[index])
    }
    return self
}
var chooseOne: Element { return self[Int(arc4random_uniform(UInt32(count)))] }
func choose(_ n: Int) -> Array { return Array(shuffled.prefix(n)) }
}

As you can see, I don't retrieve data from FireBase for this approach. So, maybe the problem was there.

Randomly generated array works only on buttons

1 Answers1