Periodically update list in swiftUI-CodePudding

I'm trying to build a macOS app that loads a list from a server and updates each list item's view every x seconds.

I browsed some existing code and followed some tutorials as I am still learning but I can't seem to figure out what's going wrong.

I have a Store that holds the data and updates it periodically like so:

class Store: NSObject, ObservableObject {
    @Published var items: [Item]
    var timer: Timer = Timer()

    override init() {
        var newItems: [Item] = []
        // updateList calls the web service and receives a `[Item]`
        updateList(update: { i in
            newItems = i
        })
        items = newItems
    
        super.init()
    
        startTimer()
    }

    func startTimer() {
        self.timer = Timer.scheduledTimer(withTimeInterval: 5, repeats: true, block: { _ in
            var newList: [Item] = []
            updateList(update: { vals in
                newList = vals
            })
            self.objectWillChange.send()
            items = newList
        })
    }
}

The view looks like this:

struct ContentView: View {
    @ObservedObject var store: Store

    var body: some View {
        VStack(alignment: .leading, spacing: 12) {
            List(store.items, id: \.self) { item in
                ListRow(item: binding(for: item))
            }
        }
        .frame(minWidth: windowSize().minWidth, minHeight: windowSize().minHeight)
        .navigationTitle("Mission")
        .toolbar {
            ToolbarItem(placement: .status) {
                Button(action: { /* Show connect dialog */ }) {
                    Image(systemName: "network")
                }
            }
            ToolbarItem(placement: .primaryAction) {
                Button(action: { /* Show file chooser/magnet entry dialog */ }) {
                    Image(systemName: "plus")
                }
            }
        }
    }

    func binding(for item: Item) -> Binding<Item> {
        guard let index = store.items.firstIndex(where: { $0.id == item.id }) else {
            fatalError("Can't find in array")
        }
        return $store.items[index]
    }
}

struct ListRow: View {
    @Binding var item: Item
    var body: some View {
        Text(item.name)
            .padding(.all, 20)
    }
}

When I run the app, it's an empty list. I can add breakpoints and I can see the list of items is getting sent around properly so I have a feeling I'm doing something wrong with the list view itself, but I'm not sure. The only thing I know for sure is that my updateList method is 100% returning a list of Items. Any ideas?

CodePudding user response：

Although you do not show enough of the code to replicate your issue, especially what updateList does, try something like this (untested code):

class Store: NSObject, ObservableObject {
    @Published var items: [Item] = [] // <-- here
    var timer: Timer = Timer()

    override init() {
        super.init()
        // updateList calls the web service and receives a `[Item]`
        updateList(update: { vals in // <-- here
            self.items = vals       // <-- here
        })
        startTimer()
    }

    func startTimer() {
        self.timer = Timer.scheduledTimer(withTimeInterval: 5, repeats: true, block: { _ in
            self.updateList(update: { vals in   // <-- here
                self.objectWillChange.send()    // <-- here
                self.items = vals               // <-- here
            })
        })
    }

}

You must also have before ContentView something like, @StateObject var store = Store() that you pass as ContentView(store: store).