How to let users move rows in a list

SwiftUI gives us simple hooks into lists to let us move rows around, although some of the functionality that was demonstrated at WWDC isn’t actually available in the current beta so we need a workaround.

What does work is that we can attach an onMove(perform:) modifier to items in a list, and have it call a method of our choosing when a move operation happens. That method needs to accept a source IndexSet and a destination Int, like this:

func move(from source: IndexSet, to destination: Int) {

When moving several items it’s always a good idea to move the later ones first so that you avoid moving other items and getting your indexes confused.

As an example, we could create a ContentView struct that sets up an array of three username strings, and asks SwiftUI to move them around calling a move() method. In order to activate moving – i.e., to make the drag handles appear – it also adds an edit button to the navigation view so the user can toggle editing mode.

Here’s the code:

struct ContentView : View {
    @State var users = ["Paul", "Taylor", "Adele"]

    var body: some View {
        NavigationView {
            List {
                ForEach(users.identified(by: \.self)) { user in
                    Text(user)
                }
                .onMove(perform: move)
            }
            .navigationBarItems(trailing: EditButton())
        }
    }

    func move(from source: IndexSet, to destination: Int) {
        // sort the indexes low to high
        let reversedSource = source.sorted()

        // then loop from the back to avoid reordering problems
        for index in reversedSource.reversed() { 
            // for each item, remove it and insert it at the destination
            users.insert(users.remove(at: index), at: destination)
        }
    }
}

In the WWDC session demos their move() method was just one line of code because it used an extension on Swift’s arrays that isn’t available to us – hopefully it will arrive soon!