SwiftUI @Binding 没有更新显示警报

Question

我试图在关闭工作表后显示警报。但是当我更新工作表中的@Binding 时，主页中的警报没有出现。我不知道现在有什么问题。谁能给我解释一下？是使用@Binding 的问题吗？如果这样做的方法/逻辑是错误的，我应该使用什么方法？

struct ContentView: View {
    @State private var showSheet = false
    @State var showAlert = false

    var body: some View {
        VStack {
            Text("sheet")
                .onTapGesture(perform: {
                    self.showSheet.toggle()
                })
        }
        .sheet(isPresented: $showSheet) {
            AddView(showAlert: self.$showAlert, showSheet: self.$showSheet)
        }
        .alert(isPresented: $showAlert){
            Alert(title: Text("Important message"), message: Text("Wear sunscreen"), dismissButton: .default(Text("Got it!")))
        }
    }

}
struct AddView: View {
    @Binding var showAlert: Bool
    @Binding var showSheet: Bool

    var body: some View {
        Button("Dismiss") {
            self.showSheet = false
            self.showAlert = true
        }
    }
}

Answer 1

Sheet 具有不同的上下文，因此在原始代码中设置的警报在此处不可见。

这里是修改后的代码。使用 Xcode 12.1 / iOS 14.1 测试

struct ContentView: View {
    @State private var showSheet = false
    @State var showAlert = false

    var body: some View {
        VStack {
            Text("sheet")
                .onTapGesture(perform: {
                    self.showSheet.toggle()
                })
        }
        .sheet(isPresented: $showSheet, onDismiss: { self.showAlert = true }) {
            AddView(showSheet: self.$showSheet)
        }
        .alert(isPresented: $showAlert){
            Alert(title: Text("Important message"), message: Text("Wear sunscreen"), dismissButton: .default(Text("Got it!")))
        }
    }

}
struct AddView: View {
    @Binding var showSheet: Bool

    var body: some View {
        Button("Dismiss") {
            self.showSheet = false
        }
    }
}

Answer 2

真正的问题是您试图关闭工作表并同时显示警报。在您的代码中，如果您向警报添加 0.5 秒的延迟，它将起作用：

struct AddView: View {
        @Binding var showAlert: Bool
        @Binding var showSheet: Bool

        var body: some View {
            Button("Dismiss") {
                self.showSheet = false
                DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
                    self.showAlert = true
                }
            }
        }
    }

不过，这样写更简洁：

struct ContentView: View {

    @State private var showSheet = false
    @State var showAlert = false

    var body: some View {
        VStack {
            Button(action: {
                self.showSheet.toggle()
            }, label: {
                Text("sheet")
            })
            .accentColor(.primary)
        }
        .sheet(isPresented: $showSheet, onDismiss: showAlertFunction, content: {
            AddView()
        })
        .alert(isPresented: $showAlert){
            Alert(title: Text("Important message"), message: Text("Wear sunscreen"), dismissButton: .default(Text("Got it!")))
        }
    }
    
    func showAlertFunction() {
        showAlert.toggle()
    }

}

struct AddView: View {

    @Environment(\.presentationMode) var presentationMode
    
    var body: some View {
        Button("Dismiss") {
            self.presentationMode.wrappedValue.dismiss()
        }
    }
}