来自 watchOS 中 if 条件 { Text() } 的 SwiftUI 运行时错误答案

【问题标题】：SwiftUI Runtime Error from if condition { Text() } in watchOS来自 watchOS 中 if 条件 { Text() } 的 SwiftUI 运行时错误
【发布时间】：2021-03-07 06:12:27
【问题描述】：

就我所读到的条件视图而言，这段代码应该可以工作。但事实并非如此。

struct Consts {
    static let myCondition = false //no difference if true or false
}

struct ContentView: View {
    @State var toggle: Bool = false
    var body: some View {
        List() {
            Text("Short Text is in first line")
            Text("Second Line Text is a little longer but not much")
            if Consts.myCondition {
                Text("This is a conditional text. As in: when the user hasn't purchased the option he / she don't need a hint how to use this feature.")
//            } else {
//                Text("else doesn't help either.")
            }
            Toggle("I also have a toggle but it has nothing to do with this.", isOn: $toggle)
            Text("Here we have a longer Text. Dont know what to type any more.")
            Text("More text which is longer than a few lines.")
            Text("Not so long Text")
        }
        .navigationTitle("Hints & Settings")
    }
}

它编译时没有警告或错误。它在模拟器和设备上加载并显示良好。但是每次我从末尾向上滚动列表时，只要这个if condition { Text() } 变得可见，应用就会崩溃

Fatal error: file SwiftUI, line 0
2021-03-07 06:36:26.548126+0100 WTFif WatchKit Extension[23163:641812] Fatal error: file SwiftUI, line 0

这不仅限于 watchOS。它在 iOS 中以相同的方式重现，只是文本必须更长，以便 if condition { Text() } 在滚动时变得不可见。

我已经用一个数组、条件范围和两个 ForEach() 块解决了这个错误。

struct ContentView: View {
    let myHints = ["Short Text is in first line",
                   "Second Line Text is a little longer but not much",
                   "This is a conditional text. As in: when the user hasn't purchased the option he / she don't need to hint how to use this feature.",
                   "Here we have a longer Text. Dont know what to type any more.",
                   "More text which is longer than a few lines.",
                   "Not so long Text"]
    var myUpperRange: ClosedRange<Int> {
        if Consts.myCondition {
            return 0...1
        } else {
            return 0...2
        }
    }
    var myLowerRange: ClosedRange<Int> {
        return 3...5
    }
    @State var toggle: Bool = false
    var body: some View {
        List() {
            ForEach (myUpperRange, id: \.self) { i in
                Text(myHints[i])
            }
            Toggle("I also have a toggle but it has nothing to do with this.", isOn: $toggle)
            ForEach (myLowerRange, id: \.self) { i in
                Text(myHints[i])
            }
        }
        .navigationTitle("Hints & Settings")
    }
}

我的问题基本上是：我没有得到它还是我在 Xcode / SwiftUI 中发现了一个错误？我上面的代码应该工作吗？我可以做些什么不同的事情来让它与简单的文本列表一起工作？

背景：我还有一个带有if condition { MyTab() } 的 TabView，它可以正常工作而不会崩溃。我是否必须担心这可能会以同样的方式崩溃？我是否也应该在发货前解决这个问题？

PS：我使用的是 Xcode 12.4 (12D4e)

【问题讨论】：

标签： swiftui swiftui-list

【解决方案1】：

显然，iOS 15 Beta 4 已解决此问题：在我的测试设备上，使用 Xcode 13 Beta 3 编译的测试应用程序在 Beta 4 更新之前出现错误。更新到 iOS 15 Beta 4 后出现错误离开了。所以我认为有理由说 iOS 15 Beta 4 的更新确实修复了这个错误。

【讨论】：