SwiftUI 表单与数据校验：从输入状态到可访问的提交流程

import SwiftUI

private struct SignUpForm {
    var email = ""
    var password = ""
    var confirmation = ""

    func errors() -> [String: String] {
        var result: [String: String] = [:]
        let trimmedEmail = email.trimmingCharacters(in: .whitespacesAndNewlines)
        if trimmedEmail.isEmpty {
            result["email"] = "请输入邮箱"
        } else if !trimmedEmail.contains("@") {
            result["email"] = "邮箱格式不正确"
        }
        if password.count < 8 {
            result["password"] = "密码至少需要 8 个字符"
        }
        if confirmation != password {
            result["confirmation"] = "两次输入的密码不一致"
        }
        return result
    }
}

struct SignUpView: View {
    private enum Field { case email, password, confirmation }
    @State private var form = SignUpForm()
    @State private var messages: [String: String] = [:]
    @State private var showSuccess = false
    @FocusState private var focusedField: Field?

    var body: some View {
        Form {
            Section("账户信息") {
                TextField("邮箱", text: $form.email)
                    .textInputAutocapitalization(.never)
                    .keyboardType(.emailAddress)
                    .focused($focusedField, equals: .email)
                errorText(for: "email")

                SecureField("密码", text: $form.password)
                    .focused($focusedField, equals: .password)
                errorText(for: "password")

                SecureField("确认密码", text: $form.confirmation)
                    .focused($focusedField, equals: .confirmation)
                errorText(for: "confirmation")
            }
            Section {
                Button("创建账户", action: submit)
            }
        }
        .navigationTitle("注册")
        .alert("提交成功", isPresented: $showSuccess) {
            Button("好的", role: .cancel) {}
        }
    }

    @ViewBuilder
    private func errorText(for key: String) -> some View {
        if let message = messages[key] {
            Text(message).font(.footnote).foregroundStyle(.red)
        }
    }

    private func submit() {
        messages = form.errors()
        guard messages.isEmpty else {
            if messages["email"] != nil { focusedField = .email }
            else if messages["password"] != nil { focusedField = .password }
            else { focusedField = .confirmation }
            return
        }
        // 这里替换为实际的 async 请求，并在请求中处理服务器错误。
        showSuccess = true
    }
}