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Preparing for checkout

Paul Hudson    @twostraws   

The final screen in our app is CheckoutView, and it’s really a tale of two halves: the first half is the basic user interface, which should provide little real challenge for you; but the second half is all new: we need to encode our Order class to JSON, send it over the internet, and get a response.

We’re going to look at the whole encoding and transferring chunk of work soon enough, but first let’s tackle the easy part: giving CheckoutView a user interface. More specifically, we’re going to create a ScrollView with an image, the total price of their order, and a Place Order button to kick off the networking.

For the image, I’ve uploaded a cupcake image to my server that we’ll load remotely with AsyncImage – we could store it in the app, but having a remote image means we can dynamically switch it out for seasonal alternatives and promotions.

As for the order cost, we don’t actually have any pricing for our cupcakes in our data, so we can just invent one – it’s not like we’re actually going to be charging people here. The pricing we’re going to use is as follows:

  • There’s a base cost of $2 per cupcake.
  • We’ll add a little to the cost for more complicated cakes.
  • Extra frosting will cost $1 per cake.
  • Adding sprinkles will be another 50 cents per cake.

We can wrap all that logic up in a new computed property for Order, like this:

var cost: Double {
    // $2 per cake
    var cost = Double(quantity) * 2

    // complicated cakes cost more
    cost += (Double(type) / 2)

    // $1/cake for extra frosting
    if extraFrosting {
        cost += Double(quantity)
    }

    // $0.50/cake for sprinkles
    if addSprinkles {
        cost += Double(quantity) / 2
    }

    return cost
}

The actual view itself is straightforward: we’ll use a VStack inside a vertical ScrollView, then our image, the cost text, and button to place the order.

We’ll be filling in the button’s action in a minute, but first let’s get the basic layout done – replace the existing body of CheckoutView with this:

ScrollView {
    VStack {
        AsyncImage(url: URL(string: "https://hws.dev/img/cupcakes@3x.jpg"), scale: 3) { image in
                image
                    .resizable()
                    .scaledToFit()
        } placeholder: {
            ProgressView()
        }
        .frame(height: 233)

        Text("Your total is \(order.cost, format: .currency(code: "USD"))")
            .font(.title)

        Button("Place Order", action: { })
            .padding()
    }
}
.navigationTitle("Check out")
.navigationBarTitleDisplayMode(.inline)

That should all be old news for you by now, but before we're done with this screen I want to show you a small but useful SwiftUI modifier we can add here: scrollBounceBehavior().

Using scroll views is a great way to make sure your layouts work great no matter what Dynamic Type size the user has enabled, but it creates a small annoyance: when your views fit just fine on a single screen, they still bounce a little when the user moves up and down on them.

The scrollBounceBehavior() modifier helps us disable that bounce when there is nothing to scroll. Add this below navigationBarTitleDisplayMode():

.scrollBounceBehavior(.basedOnSize)

With that in place we'll get nice scroll bouncing when we have actually scrolling content, otherwise the scroll view acts like it isn't even there.

With that last tweak out of the way, it's time to finish up this project by tackling the tricky part: networking!

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