SwiftUI: LazyVStack does not update

Question

Im my app I have a ScrollView with a LazyVStack inside.

The ForEach inside takes an array of DailyEvents:

struct DailyEvents: Equatable, Identifiable {
    var id: String {
        dayString + "\(events.count)"
    }
    let day: Date
    let events: [EventInfo]

    var isToday: Bool {
        day.isToday()
    }

    var dateString: String {
        DateFormatter.dayMonthDateFormtter.string(from: day)
    }

    var dayString: String {
        isToday ? "today".localized : DateFormatter.dayDateFormtter.string(from: day)
    }
}

So every time I add a new DailyEvents in the array, the LazyVStack updates properly.

But if I add a new EventInfo inside the events property of a DailyEvents already existing. The LazyVstack does not see the update and it does not reload.

If I switch LazyVstack for a VStack, everything works properly.

UI:

@ObservedObject var viewModel: ViewModel
var scrollViewProxy = ScrollViewProxyManager()
@SwiftUI.State private var isBackToTodayVisible = false

private var events: [DailyEvents] {
  viewModel.dailyEvents.value ?? []
}
var eventsList: some View {
            ZStack(alignment: .bottom) {
                ScrollView {
                    ScrollViewReader { proxy in
                        LazyVStack(alignment: .center, spacing: 0) {
                            Spacer()
                                .frame(height: 16)
                            ForEach(events, id: \.id) { dailyEvent in
                                makeDailyEvents(dailyEvent)
                            }
                        }
                        .onAppear {
                            scrollViewProxy.setProxy(proxy: proxy)
                        }
                    }
                }
                if isBackToTodayVisible {
                    scrollTodayButton
                        .padding(.bottom, 16)
                }
            }
        }

Would you show how do you do the update, your events are constant property? — Asperi
– Asperi, Commented Jun 4, 2021 at 11:25
Computable properties do not update body, there should be stored dynamic property. — Asperi
– Asperi, Commented Jun 4, 2021 at 11:44
nope, I just remove the computed property, and I still have the same problem... I get the updates only if I scroll up and down — Andre
– Andre, Commented Jun 4, 2021 at 12:00

Teja Kumar Bethina · Accepted Answer · 2022-08-19 07:23:54Z

11

There is no alternative to UIKit UITableView's reloadData() method in SWIFTUI, to reload list/LazyStack data.

I faced exactly the same issue where the List or LazyVStack UI not updated when data-source updates.[here data-source should be @ObservedObject/@State]

I used a simple trick which fixed this issue -- assign a Unique ID to the view like below.

List(items, id: \.self) {
   Text($0.name)
}
.id(UUID())

Example with LazyVStack:

LazyVStack {
  ForEach(items, id: \.self) { item in
    Text(item.name)
  }
}
.id(UUID())

edited Aug 19, 2022 at 7:23

answered Aug 19, 2022 at 7:14

Teja Kumar Bethina

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1 Comment

Samuel Folledo Over a year ago

Broooo that hoops I had to jump to get my data to refresh and this id was all I needed 😭

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