当我在 SwiftUI 中单击 Picker 两次时应用程序崩溃？

Question

Trying to follow some tutorial and made my first picker

    struct ContentView: View {
    @State var unitEntry = ""
    @State var unitInput = ""
    @State var unitOutput = 0

    let units = ["Celsius", "Fahrenheit", "Kelvin"];

    var body: some View {
        NavigationView{
            Form{
                Text("Hello, World!")

                TextField("Test", text: $unitEntry)
                    .keyboardType(.decimalPad)

                Picker("Entry unit", selection: $unitInput) {
                    Text("Hello, World!")
                    Text("Hello, World2!")
                }
            }
        }
    }
}

The picker works, it goes to another view to pick between the two text options. But when I go back and tap the picker again it crashes.

2020-01-19 18:32:38.593660-0500 UnitConversion[46718:2939869] [TableView] Warning once only: UITableView was told to layout its visible cells and other contents without being in the view hierarchy (the table view or one of its superviews has not been added to a window). This may cause bugs by forcing views inside the table view to load and perform layout without accurate information (e.g. table view bounds, trait collection, layout margins, safe area insets, etc), and will also cause unnecessary performance overhead due to extra layout passes. Make a symbolic breakpoint at UITableViewAlertForLayoutOutsideViewHierarchy to catch this in the debugger and see what caused this to occur, so you can avoid this action altogether if possible, or defer it until the table view has been added to a window. Table view: <_TtC7SwiftUIP33_BFB370BA5F1BADDC9D83021565761A4925UpdateCoalescingTableView: 0x7fe0e2086600; baseClass = UITableView; frame = (0 0; 414 896); clipsToBounds = YES; autoresize = W+H; gestureRecognizers = <NSArray: 0x600002677f60>; layer = <CALayer: 0x6000028af160>; contentOffset: {0, -140}; contentSize: {414, 161.00000000000003}; adjustedContentInset: {140, 0, 34, 0}; dataSource: <_TtGC7SwiftUIP13$7fff2c69da4419ListCoreCoordinatorGVS_20SystemListDataSourceOs5Never_GOS_19SelectionManagerBoxS2___: 0x7fe0bdc3e7c0>>
2020-01-19 18:32:40.477829-0500 UnitConversion[46718:2939869] Can't find keyplane that supports type 8 for keyboard iPhone-PortraitTruffle-DecimalPad; using 25739_PortraitTruffle_iPhone-Simple-Pad_Default
2020-01-19 18:32:40.504773-0500 UnitConversion[46718:2939869] Can't find keyplane that supports type 8 for keyboard iPhone-PortraitTruffle-DecimalPad; using 25739_PortraitTruffle_iPhone-Simple-Pad_Default

Answer 1

Actually the pickier in you case I assume should look like below and log which you provided does not refer to crash, if any, it is just a warning (as it stated) and originated not by your code but SwiftUI internals, so can be ignored for now (or submit Apple feedback)

@State var unitInput = "Celsius"

Picker("Entry unit", selection: $unitInput) {
    ForEach(units, id: \.self) { unit in
        Text(unit)
    }
}

Answer 2

I believe it should be ok if you run it on a physical device. I believe it is a bug in the simulator.