SwiftUI纯结构体代码下修复@State越界访问警告的方法

编译时，以下代码的第1行会触发警告：

Accessing State's value outside of being installed on a View. This will result in a constant Binding of the initial value and will not update.

原代码：

import SwiftUI

struct MyView: View {

    enum Status {
        case a, b
    }

    struct MyButton: Identifiable {
        let id = UUID()
        @State var status: Status = .a
        let action: (Binding<Status>)->Void
    }

    @State var buttons: [MyButton] = [
        MyView.MyButton(action: { status in
            status.wrappedValue = .b
        })
    ]
    
    var body: some View {
        VStack {
            ForEach(buttons) { button in
                Button("x") {
                    button.action(button.$status) // #1
                }
                .disabled(button.status == .b)
            }
        }
    }
}

struct MyView_Previews: PreviewProvider {
    static var previews: some View {
        MyView()
    }
}

运行时点击按钮，按钮不会变为禁用状态，和警告描述一致。现有相关解决方案多依赖类和@ObservableObject，以下提供**纯结构体、不使用类与@ObservableObject**的修复方案，同时保留「在按钮动作中设置禁用状态」的核心逻辑。

问题根源 #

@State是SwiftUI专为View设计的属性包装器，仅当它被直接附着在View结构体中时，才能被SwiftUI的状态系统正确追踪。原代码中@State var status放在非View的MyButton结构体里，且该结构体被父View的@State数组持有，导致状态无法被正确关联到View层级，访问button.$status时只能拿到初始值的常量绑定，无法响应后续修改。

纯结构体修复方案 #

方案一：父View集中管理按钮状态 #

将按钮的状态从MyButton中剥离，统一由父View用字典管理，通过Binding关联到每个按钮：

import SwiftUI

struct MyView: View {
    enum Status {
        case a, b
    }
    
    // 仅存储按钮的静态配置
    struct MyButtonConfig: Identifiable {
        let id = UUID()
        let action: (Binding<Status>) -> Void
    }
    
    @State private var buttonConfigs: [MyButtonConfig] = [
        MyButtonConfig(action: { status in
            status.wrappedValue = .b
        })
    ]
    // 用字典存储每个按钮的状态，键为按钮ID
    @State private var buttonStatuses: [UUID: Status] = [:]
    
    var body: some View {
        VStack {
            ForEach(buttonConfigs) { config in
                // 自定义Binding，关联父View的状态字典
                let statusBinding = Binding(
                    get: { buttonStatuses[config.id] ?? .a },
                    set: { buttonStatuses[config.id] = $0 }
                )
                
                Button("x") {
                    config.action(statusBinding)
                }
                .disabled(statusBinding.wrappedValue == .b)
            }
        }
        .onAppear {
            // 初始化所有按钮的默认状态
            buttonConfigs.forEach {
                if buttonStatuses[$0.id] == nil {
                    buttonStatuses[$0.id] = .a
                }
            }
        }
    }
}

struct MyView_Previews: PreviewProvider {
    static var previews: some View {
        MyView()
    }
}

方案二：将MyButton封装为独立View #

让MyButton成为View结构体，内部的@State就能被SwiftUI正确安装和追踪：

import SwiftUI

struct MyView: View {
    enum Status {
        case a, b
    }
    
    // 将MyButton改为View，内部@State由SwiftUI管理
    struct MyButton: View, Identifiable {
        let id = UUID()
        @State private var status: Status = .a
        let action: (Binding<Status>) -> Void
        
        var body: some View {
            Button("x") {
                action($status)
            }
            .disabled(status == .b)
        }
    }
    
    @State private var buttons: [MyButton] = [
        MyButton(action: { status in
            status.wrappedValue = .b
        })
    ]
    
    var body: some View {
        VStack {
            ForEach(buttons) { button in
                button // 直接渲染MyView，状态由内部@State自行管理
            }
        }
    }
}

struct MyView_Previews: PreviewProvider {
    static var previews: some View {
        MyView()
    }
}

内容的提问来源于stack exchange，提问作者Manuel