Delay in For Loop Swift

Question

I am creating a simple card game (Set) in SwiftUI. I have a button that will deal X new cards when tapped. Currently, it makes all cards show up at once. I was wondering how I could make them come out one at a time.

Deal works by appending a new card to a Deck array in the model. ContentView displays each card in the grid.

This is what I currently have after looking online. Displays first card then next all at once

func deal(_ numberOfCards: Int) {
        withAnimation(Animation.easeInOut(duration: 1)) {
            viewModel.deal()
        }
        for _ in 1..<numberOfCards {
            DispatchQueue.main.asyncAfter(deadline: .now() + 0.7) {
                withAnimation(.easeInOut) {
                    viewModel.deal()
                }
            }
        }
    }

Look into creating a custom queue with all the items enqueued up, and then execute the queue after your loop. Or better, since you're using animations, use a keyframe animation? — Claus Jørgensen
– Claus Jørgensen, Commented Jun 28, 2020 at 21:28

Tomo Norbert · Accepted Answer · 2020-06-28 21:50:22Z

2

Try this

func deal(_ numberOfCards: Int) {
    withAnimation(Animation.easeInOut(duration: 1)) {
        viewModel.deal()
    }
    for i in 1..<numberOfCards {
        DispatchQueue.main.asyncAfter(deadline: .now() + Double(i) * 0.7) {
            withAnimation(.easeInOut) {
                viewModel.deal()
            }
        }
    }
}

edited Jun 28, 2020 at 21:50

answered Jun 28, 2020 at 21:26

Tomo Norbert

7804 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Rob · Accepted Answer · 2020-06-29 19:55:34Z

The problem is that you’re starting all of them 0.7 seconds from now. You want to multiply that interval by the for loop index. You can probably also simplify it a bit, e.g.:

func deal(_ numberOfCards: Int) {
    for i in 0..<numberOfCards {
        DispatchQueue.main.asyncAfter(deadline: .now() + Double(i) * 0.7) {
            withAnimation(.easeInOut) {
                viewModel.deal()
            }
        }
    }
}

This pattern isn’t ideal, though, because if you dismiss the view in question, it’s still going to be trying to flip cards on view that isn’t present anymore. Also, this pattern of issuing multiple asyncAfter is not great because it’s subject to timer coalescing (where latter calls may be coalesced together to save battery). This latter issue might not be an issue here, but as a general rule, we use Timer to prevent coalescing and to be able to cancel the timer when the view is dismissed.

func deal(_ numberOfCards: Int) {
    var cardNumber = 0
    let timer = Timer.scheduledTimer(withTimeInterval: 0.7, repeats: true) { timer in
        withAnimation(.easeInOut) {
            viewModel.deal()
        }
        
        cardNumber += 1
        if cardNumber >= numberOfCards {
            timer.invalidate()
        }
    }
    timer.fire()
}

If this was in a class, I might use [weak self] in the timer closure with

guard let self = self else {
    timer.invalidate()
    return
}

Collectives™ on Stack Overflow

Delay in For Loop Swift

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related