SwiftUI：如何使用 .presentation 修饰符进行警报？获取编译器类型检查错误

Question

为了好玩，我正在将我在 UIKit 中制作的测验应用程序重新构建到 SwiftUI 中，我 运行 进入编译器错误，因为我在下面有最后一个 .presentation 修饰符。

我不确定如何分解它。看起来很简单。 运行 2012 款 MacBook Pro Retina i7。

@State var showingSaveAlert = false
@State var showingLoadSaveAlert = false


var loadProgress: Alert {
        Alert(title: Text("Load Progress?"), message: Text("Continue from question \(studySaver)?"), primaryButton: .default(Text("Load"), onTrigger: {
            self.loadProgressHandler()
        }), secondaryButton: .cancel())
    }

    var savedAlert: Alert {
        Alert(title: Text("Saved!"), message: Text("Your place has been saved. You may now leave this page without loosing progress."), dismissButton: .cancel())
    }


//MARK: SwiftUI
var body: some View {
        VStack{

        // Bunch of Swift UI Code within the VStack
        ...

            }
            .navigationBarTitle(Text(subject + " Test"), displayMode: .inline)
            .navigationBarItems(trailing:
                Button(action: {
                    self.showingSaveAlert = true
                    self.save()
                    print("Saved")
                }) {
                    Text("Save")
                    }
                    .presentation(showingSaveAlert ? savedAlert : nil)
            )
            .onAppear(){
                print("Test Page Appeared")
                self.showingLoadSaveAlert = true
                self.showingContinue = false
                self.questionLoader()
            }
            .presentation(showingLoadSaveAlert ? loadProgress : nil)


    } //MARK: End of SwiftUI

I would expect it to clear but I get a type-check error on the last modifier .presentation(showingLoadSaveAlert ? loadProgress : nil)

Error:
"The compiler is unable to type-check this expression in reasonable time; try breaking up the expression into distinct sub-expressions"

The main goal is to get an alert to show up when the View appears asking to load a save for a quiz.

Any thoughts?

Answer 1

问题出在这一行：（以及其他警报显示代码）

.presentation(showingSaveAlert ? savedAlert : nil)

警报应该 绑定 到 SwiftUI 中的 Bool。

改成这样：

.presentation($showingSaveAlert) { savedAlert }