Day 11 · 2부 · @FocusState와 폼 모델 검증

import UIKit

final class LoginViewController: UIViewController, UITextFieldDelegate {
    private let emailField = UITextField()
    private let passwordField = UITextField()

    override func viewDidLoad() {
        super.viewDidLoad()
        emailField.delegate = self
        emailField.returnKeyType = .next
        passwordField.delegate = self
        passwordField.isSecureTextEntry = true
        passwordField.returnKeyType = .go
    }

    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        if textField === emailField {
            passwordField.becomeFirstResponder()   // 다음 칸으로
        } else {
            textField.resignFirstResponder()       // 키보드 내림
        }
        return true
    }
}

struct SearchBox: View {
    @State private var query = ""
    @FocusState private var isFocused: Bool

    var body: some View {
        HStack {
            TextField("검색", text: $query)
                .textFieldStyle(.roundedBorder)
                .focused($isFocused)
            if isFocused {
                Button("취소") {
                    query = ""
                    isFocused = false      // resignFirstResponder 대신
                }
            }
        }
        .padding()
        .animation(.default, value: isFocused)
    }
}

struct LoginForm: View {
    enum Field: Hashable { case email, password }

    @State private var email = ""
    @State private var password = ""
    @FocusState private var focusedField: Field?

    var body: some View {
        Form {
            TextField("이메일", text: $email)
                .focused($focusedField, equals: .email)
                .keyboardType(.emailAddress)
                .textInputAutocapitalization(.never)
                .submitLabel(.next)                 // 키보드 Return 자리에 "다음"
                .border(focusedField == .email && !isEmailValid ? .red : .clear)
            SecureField("비밀번호", text: $password)
                .focused($focusedField, equals: .password)
                .submitLabel(.go)
        }
        .onSubmit {                                 // Form 안의 어느 칸이든 Return이면 호출
            if focusedField == .email {
                focusedField = .password            // 다음 칸으로
            } else {
                signIn()
            }
        }
    }

    private var isEmailValid: Bool { email.contains("@") }

    private func signIn() {
        guard isEmailValid else {
            focusedField = .email                   // 문제 있는 칸으로 되돌림
            return
        }
        focusedField = nil                          // 키보드 내리고 로그인 진행
    }
}

import UIKit

struct CloseKeyboardLegacy: View {
    @State private var text = ""

    var body: some View {
        VStack {
            TextField("메모", text: $text)
            Button("닫기") {
                UIApplication.shared.sendAction(
                    #selector(UIResponder.resignFirstResponder),
                    to: nil, from: nil, for: nil)
            }
        }
    }
}

struct TransferForm: View {
    enum Field: Hashable { case amount, memo }

    @State private var amount = ""
    @State private var memo = ""
    @FocusState private var focused: Field?

    var body: some View {
        NavigationStack {
            Form {
                TextField("금액", text: $amount)
                    .keyboardType(.numberPad)         // Return 키가 없다 → 툴바가 필요
                    .focused($focused, equals: .amount)
                TextField("메모", text: $memo)
                    .focused($focused, equals: .memo)
                    .submitLabel(.done)
            }
            .scrollDismissesKeyboard(.interactively)  // 끌어내리면 키보드도 따라 내려감
            .toolbar {
                ToolbarItemGroup(placement: .keyboard) {
                    Button("다음") { focused = .memo }
                        .disabled(focused == .memo)
                    Spacer()
                    Button("완료") { focused = nil }
                }
            }
            .navigationTitle("송금")
        }
    }
}

struct PostForm: View {
    @State private var title = ""
    @State private var tags = ""

    var body: some View {
        Form {
            TextField("제목", text: $title)
            TextField("태그 (쉼표로 구분)", text: $tags)
                .submitScope()          // 이 칸의 제출은 위쪽 onSubmit에 닿지 않는다
        }
        .onSubmit { save() }            // 제목 칸 Return → 저장
    }

    private func save() { print("저장: \(title)") }
}

import Observation

enum SignUpField: Hashable { case name, email }

@Observable
final class SignUpModel {
    var name = ""
    var email = ""
    var age = 20
    var agreed = false
    var touched: Set<SignUpField> = []      // 사용자가 거쳐 간 칸

    var nameError: String? {
        name.trimmingCharacters(in: .whitespaces).isEmpty ? "이름을 입력하세요" : nil
    }
    var emailError: String? {
        email.contains("@") && email.contains(".") ? nil : "이메일 형식이 아니다"
    }
    var isValid: Bool {
        nameError == nil && emailError == nil && agreed
    }
}

struct SignUpView: View {
    @State private var model = SignUpModel()
    @FocusState private var focused: SignUpField?

    var body: some View {
        Form {
            Section {
                TextField("이름", text: $model.name)
                    .focused($focused, equals: .name)
                    .submitLabel(.next)
                if model.touched.contains(.name), let error = model.nameError {
                    Text(error).font(.footnote).foregroundStyle(.red)
                }
                TextField("이메일", text: $model.email)
                    .focused($focused, equals: .email)
                    .keyboardType(.emailAddress)
                    .textInputAutocapitalization(.never)
                    .submitLabel(.done)
                if model.touched.contains(.email), let error = model.emailError {
                    Text(error).font(.footnote).foregroundStyle(.red)
                }
            }
            Section {
                Stepper("나이 \(model.age)", value: $model.age, in: 14...120)
                Toggle("약관에 동의", isOn: $model.agreed)
            }
            Button("가입하기") { focused = nil }
                .disabled(!model.isValid)               // 계산값 하나로 막는다
        }
        .onSubmit {
            focused = (focused == .name) ? .email : nil
        }
        .onChange(of: focused) { oldValue, _ in
            if let oldValue { model.touched.insert(oldValue) }   // 방금 떠난 칸
        }
    }
}

struct AgreementRow: View {
    @Bindable var model: SignUpModel

    var body: some View {
        Toggle("약관에 동의", isOn: $model.agreed)
    }
}

struct EmailFormWrong: View {
    @State private var email = "a@b.com"
    @State private var isValid = false          // 초기값부터 이미 틀렸다

    var body: some View {
        Form {
            TextField("이메일", text: $email)
                .onChange(of: email) { _, newValue in
                    isValid = newValue.contains("@")
                }
            Button("보내기") { }.disabled(!isValid)
        }
    }
}

struct EmailForm: View {
    @State private var email = "a@b.com"
    private var isValid: Bool { email.contains("@") }

    var body: some View {
        Form {
            TextField("이메일", text: $email)
            Button("보내기") { }.disabled(!isValid)
        }
    }
}

struct NameFieldsWrong: View {
    enum Field: Hashable { case name, fullName }
    @State private var name = ""
    @State private var fullName = ""
    @FocusState private var focused: Field?

    var body: some View {
        VStack {
            TextField("이름", text: $name)
                .focused($focused, equals: .name)
            TextField("전체 이름", text: $fullName)
                .focused($focused, equals: .name)   // .fullName이어야 한다
        }
    }
}

struct AddressForm: View {
    @State private var receiver = ""
    @State private var phone = ""
    @State private var address = ""

    var body: some View {
        NavigationStack {
            Form {
                TextField("받는 분", text: $receiver)
                TextField("전화번호", text: $phone)
                TextField("주소", text: $address)
                Button("저장") { }
            }
            .navigationTitle("배송지")
        }
    }
}

#Preview { AddressForm() }