SwiftUI问题：视图状态变更时FocusState自动唤起键盘

问题核心是视图状态切换到.error时，SwiftUI重新渲染对应视图分支，焦点状态被意外保留，导致键盘自动弹出。可以通过以下两种方式解决：

方法一：在错误状态视图分支中主动清除焦点 #

直接在.error对应的视图上添加onAppear，触发时清空焦点状态：

struct SignInUI: View {
    @State var email: String = ""
    @State var password: String = ""
    private enum Field: Int, CaseIterable {
        case username, password
    }
    @FocusState private var focusedField: Field?
    @StateObject var viewModel: SignInViewModel
    
    var body: some View {
        Group {
            switch viewModel.state {
            case .loading:
                ZStack {
                    content
                    ProgressView()
                }
                
            case .error:
                ZStack {
                    content
                    ErrorView()
                }
                // 进入错误状态时清空焦点，收起键盘
                .onAppear {
                    focusedField = nil
                }
                
            case .loaded:
                content
            }
        }
    }
    
    var content: some View {
        VStack {
            PasswordTextField(field: $password)
                .focused($focusedField, equals: .password)
            EmailTextField(field: $email)
                .focused($focusedField, equals: .username)
            
            ButtonView(text: "Sign In", action: {
                focusedField = nil
                viewModel.signIn(email: email, password: password)
            })
        }
    }
}

方法二：监听状态变化统一处理 #

如果需要在多个状态切换场景下处理焦点，可以用onChange监听viewModel.state的变化：

struct SignInUI: View {
    @State var email: String = ""
    @State var password: String = ""
    private enum Field: Int, CaseIterable {
        case username, password
    }
    @FocusState private var focusedField: Field?
    @StateObject var viewModel: SignInViewModel
    
    var body: some View {
        Group {
            switch viewModel.state {
            case .loading:
                ZStack {
                    content
                    ProgressView()
                }
                
            case .error:
                ZStack {
                    content
                    ErrorView()
                }
                
            case .loaded:
                content
            }
        }
        // 监听状态变化，进入错误状态时清空焦点
        .onChange(of: viewModel.state) { newState in
            if newState == .error {
                focusedField = nil
            }
        }
    }
    
    var content: some View {
        VStack {
            PasswordTextField(field: $password)
                .focused($focusedField, equals: .password)
            EmailTextField(field: $email)
                .focused($focusedField, equals: .username)
            
            ButtonView(text: "Sign In", action: {
                focusedField = nil
                viewModel.signIn(email: email, password: password)
            })
        }
    }
}

原理说明 #

FocusState绑定的focusedField直接控制TextField的焦点状态，将其设为nil会让所有绑定的TextField失去焦点，系统会自动收起键盘。在视图切换到错误状态时主动触发这个操作，就能避免键盘意外弹出。

内容的提问来源于stack exchange，提问作者Marta Paniti