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Adding swipe to delete and EditButton

Paul Hudson    @twostraws   

Fully updated for Xcode 11 GM

Before we’re done with this app, let’s make a handful of smaller changes that help polish up what we have.

First, what happens if the user looks at their order and decides against one of the items? Right now we can add items but can’t delete them, but this isn’t too hard to remedy.

Just like UIKit, SwiftUI works with tables using IndexSet – a collection of locations in its data. So, we can add a method to OrderView that accepts an IndexSet and uses it to delete those items from our order array:

func deleteItems(at offsets: IndexSet) {
    order.items.remove(atOffsets: offsets)
}

To connect that to SwiftUI, we need to add an onDelete() modifier to the ForEach that shows the menu items in the order. This accepts a closure that will be executed when deletion happens, and that closure must accept an IndexSet and delete those items – basically exactly what our deleteItems(at:) method already does.

Modify the first section in the OrderView form to this:

Section {
    ForEach(order.items) { item in
        HStack {
            Text(item.name)
            Spacer()
            Text("$\(item.price)")
        }
    }.onDelete(perform: deleteItems)
}

If the user wants to remove several items at a time, that’s also easy to do in SwiftUI. We just added the method to handle deletion, so now we can add an edit button to the navigation bar and let SwiftUI handle the rest. No, really!

Add this after the .listStyle(GroupedListStyle()) modifier in OrderView:

.navigationBarItems(trailing: EditButton())

SwiftUI already knows that an edit button should toggle the table between editing and non-editing mode, while also changing title between Edit and Done – another example of us getting the system default behavior for free.

Let’s move on to a second upgrade: why do we let users press the Place Order button if they haven’t added anything to their order? This doesn’t make sense, and we shouldn’t really allow it. So, let’s not allow it!

Here’s how that part of OrderView looks right now:

Section {
    NavigationLink(destination: CheckoutView()) {
        Text("Place Order")
    }
}

What we want is to disable that when there are no items in our order. Well, thanks to the power of SwiftUI we can do exactly that with the disabled() modifier, like this:

Section {
    NavigationLink(destination: CheckoutView()) {
        Text("Place Order")
    }
}.disabled(order.items.isEmpty)

If you run the app now you’ll find that you can add an item, go to the order screen, and delete that item, and Place Order will automatically become disabled as your cart becomes empty.

Finally, we’re displaying the total for our order in CheckoutView, but it’s not particularly prominent. To finish up, let’s bump up that text size:

Section(header:
    Text("TOTAL: $\(totalPrice, specifier: "%.2f")")
        .font(.largeTitle)
) {

Much better!

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