如何在 SwiftUI 的一个视图上有两个警报? [英] How can I have two alerts on one view in SwiftUI?

问题描述

我希望将两个独特的警报附加到同一个 Button 视图.当我使用下面的代码时，只有底部的警报有效.

I want to have two unique alerts attached to the same Button view. When I use the code below, only the alert on the bottom works.

我在 macOS Catalina 上使用官方发布的 Xcode 11.

I'm using the official release of Xcode 11 on macOS Catalina.

@State private var showFirstAlert = false
@State private var showSecondAlert = false

Button(action: {
    if Bool.random() {
        showFirstAlert = true
    } else {
        showSecondAlert = true
    }
}) {
    Text("Show random alert")
}
.alert(isPresented: $showFirstAlert) {
    // This alert never shows
    Alert(title: Text("First Alert"), message: Text("This is the first alert"))
}
.alert(isPresented: $showSecondAlert) {
    // This alert does show
    Alert(title: Text("Second Alert"), message: Text("This is the second alert"))
}

当我将 showFirstAlert 设置为 true 时，我希望显示第一个警报，而当我将 showSecondAlert 设置为 true 时，我希望显示第二个警报.只有第二个警报显示其状态何时为真，但第一个警报什么都不做.

I expect first alert to show when I set showFirstAlert to true and I expect the second alert to show when I set showSecondAlert to true. Only the second alert shows when its state is true but the first one does nothing.

推荐答案

对 .alert(isPresented) 的第二次调用将覆盖第一次调用.你真正想要的是一个 Binding 来表示是否出现警报，以及一些设置，哪些警报应该从 .alert(isPresented) 之后的闭包中返回.您可以为此使用 Bool，但我继续使用枚举来完成它，因为它可以扩展到两个以上的警报.

The second call to .alert(isPresented) is overriding the first. What you really want is one Binding<Bool> to denote whether the alert is presented, and some setting for which alert should be returned from the closure following .alert(isPresented). You could use a Bool for this, but I went ahead and did it with an enum, as that scales to more than two alerts.

enum ActiveAlert {
    case first, second
}

struct ToggleView: View {
    @State private var showAlert = false
    @State private var activeAlert: ActiveAlert = .first

    var body: some View {

        Button(action: {
            if Bool.random() {
                self.activeAlert = .first
            } else {
                self.activeAlert = .second
            }
            self.showAlert = true
        }) {
            Text("Show random alert")
        }
        .alert(isPresented: $showAlert) {
            switch activeAlert {
            case .first:
                return Alert(title: Text("First Alert"), message: Text("This is the first alert"))
            case .second:
                return Alert(title: Text("Second Alert"), message: Text("This is the second alert"))
            }
        }
    }
}

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