Transition animation not working in iOS16 but was working in iOS15

Question

I have a SwiftUI Form with a custom chart view (not Swift Charts). A long press toggles to a different type of chart. These charts use the .transition(.slide) modifier. In iOS 15 these transitioned as expected on a long press, but in iOS 16 they do not.

Persisted state property (an enum):

@AppStorage("chartType") var chartType: ChartType = .chartA

The Form part of the body property:

Form {
    
    // Other sections
    
    Section {
        switch chartType {
            case .chartA:
                ChartViewA()
                    .transition(.slide)
            case .chartB:
                ChartViewB()
                    .transition(.slide)
    }
        .onLongPressGesture {
            if chartType == .chartA {
                withAnimation {
                    summaryChartType = .chartB
                }
            } else {
                withAnimation {
                    summaryChartType = .chartA
                }
            }
        }

Unfortunately adding animation modifiers like .animation(.spring(), value: chartType) makes no difference.

I would be grateful for advice on why this might have worked in iOS 15 but not in iOS 16, and what I could do to restore animation here.

Answer 1

In iOS 16, there appears to be a problem with @AppStorage vars and animation. Here is one possible workaround. Use @State var for animation, and save it to an @AppStorage variable with .onChange():

enum ChartType: String {
    case chartA, chartB
}

struct ChartViewA: View {
    var body: some View {
        Color.red
    }
}

struct ChartViewB: View {
    var body: some View {
        Color.blue
    }
}

struct ContentView: View {
    @AppStorage("chartType") var chartTypeAS: ChartType = .chartA
    @State private var chartType: ChartType = .chartA
    
    init() {
        // load initial value from persistent storage
        _chartType = State(initialValue: chartTypeAS)
    }
    
    var body: some View {

        Form {
            
            // Other sections
            
            Section {
                VStack {
                    switch chartType {
                    case .chartA:
                        ChartViewA()
                            .transition(.slide)
                    case .chartB:
                        ChartViewB()
                            .transition(.slide)
                    }
                }
                .onLongPressGesture {
                    if chartType == .chartA {
                        withAnimation {
                            chartType = .chartB
                        }
                    } else {
                        withAnimation {
                            chartType = .chartA
                        }
                    }
                }
            }
            .onChange(of: chartType) { value in
                // persist chart type
                chartTypeAS = value
            }
        }
    }
}

Tested in Xcode 14.0 with iPhone 14 simulator running iOS 16.

Alternatively, you could perform the saving to/restoring from UserDefaults manually.