Preparing for checkout

Paul Hudson @twostraws February 20th 2020

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 provided two images in the files for this project, available from https://github.com/twostraws/HackingWithSwift. Look in the SwiftUI/project10-files folder, and copy both cupcakes@2x.jpg and cupcakes@3x.jpg into your asset catalog. We’ll need to use GeometryReader to size this picture to the correct width of the screen, to avoid it stretching layouts on smaller devices.

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 GeometryReader to make sure our cupcake image is sized correctly, 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:

GeometryReader { geo in
    ScrollView {
        VStack {
            Image("cupcakes")
                .resizable()
                .scaledToFit()
                .frame(width: geo.size.width)

            Text("Your total is $\(self.order.cost, specifier: "%.2f")")
                .font(.title)

            Button("Place Order") {
                // place the order
            }
            .padding()
        }
    }
}
.navigationBarTitle("Check out", displayMode: .inline)

That should all be old news for you by now. But the tricky part comes next…