根据服务器发送的内容显示 Flutter 中的任何验证错误

问：

我想根据服务器发送的内容在 Flutter 中显示任何验证错误。

1. 我想我使用try-catch太多了，它已经在API中，然后它在视野中，它也在服务中。这种方法正确吗？

2. 当我按下按钮时，出现的是以下对话框：

   发生错误：NoSuchMethodError：在 null 上调用了方法“[]”。
   接收器：null。
   尝试调用：[]（“message”）

这是我的 API 中的代码：

public function register(Request $request)
    {
        try {
            // Validasi data yang diterima dari klien
            $request->validate([
                'name' => 'required|string|max:255',
                'username' => 'required|string|max:255|unique:users',
                'email' => 'required|email|unique:users',
                'password' => 'required|string|min:6',
                'password_confirmation' => 'required|string|same:password',
            ]);
            // if ($validator->fails()) {
            //     return response()->json(['validationError' => 'Validasi gagal', 'errors' => $validator->errors()], 400);
            // }

            // Buat instance User
            $user = new User();
            $user->name = $request->input('name');
            $user->username = $request->input('username');
            $user->email = $request->input('email');
            $user->password = bcrypt($request->input('password'));
            $user->save();

            // Kirim respons dengan pesan berhasil dan data pengguna yang terdaftar
            return response()->json(['message' => 'Registrasi berhasil!', 'data' => $user], 201);
        } catch (ValidationException $e) {
            // Tangani kesalahan validasi dengan mengirim respons error dengan status 400 (Bad Request)
            return response()->json(['message' => 'Validasi gagal', 'errors' => $e->errors()], 400);
        } catch (\Exception $e) {
            // Tangani kesalahan dengan mengirim respons error
            return response()->json(['message' => 'Registrasi gagal', 'error' => $e->getMessage()], 500);
        }
    }

这是我未来的服务功能：

Future register(
      {required String name,
      required String username,
      required String email,
      required String password,
      required String password_confirmation}) async {
    final Map jsonData = {
      'name': name,
      'username': username,
      'email': email,
      'password': password,
      'password_confirmation': password_confirmation,
    };

    try {
      final Map jsonData = {
        'name': name,
        'username': username,
        'email': email,
        'password': password,
        'password_confirmation': password_confirmation,
      };
      Response response = await dio.post('$baseUrl/register', data: jsonData);
      print(response.data);

      if (response.statusCode == 201) {
        final Map<String, dynamic> resultData = response.data;
        return resultData;
      } else if (response.statusCode == 400) {
        final Map<String, dynamic> resultData = response.data;
        return resultData;
      }
    } on DioException catch (e) {
      print(e);
    }
  }

这是我视图中的代码按钮 flutter：

ElevatedButton(
                  onPressed: () async {
                    if (key.currentState!.validate()) {
                      final navigator = Navigator.of(context);

                      showDialog(
                        context: context,
                        barrierDismissible: false,
                        builder: (context) {
                          return const Center(
                              child: CircularProgressIndicator());
                        },
                      );

                      try {
                        final data = await AuthService().register(
                          name: nameC.text,
                          username: usernameC.text,
                          email: emailC.text,
                          password: passwordC.text,
                          password_confirmation: password_confirmationC.text,
                        );
                        print(data);
                        if (data["message"] == "Registrasi berhasil!") {
                          navigator.pushAndRemoveUntil(
                            MaterialPageRoute(
                              builder: (ctx) => const LoginPage(),
                            ),
                            (route) => false,
                          );
                        } else {
                          throw Error();
                        }
                      } catch (e) {
                        navigator.pop();
                        if (e is Map<String, dynamic> &&
                            e.containsKey("validationError")) {
                          // Pesan kesalahan validasi diterima dari API
                          showDialog(
                            context: context,
                            builder: (ctx) {
                              final validationErrors = e["errors"];
                              final errorMessages = validationErrors.values
                                  .expand((value) => value)
                                  .toList();
                              return AlertDialog(
                                shape: RoundedRectangleBorder(
                                  borderRadius: BorderRadius.circular(12),
                                ),
                                title: Text('Registrasi Gagal'),
                                content: Column(
                                  crossAxisAlignment: CrossAxisAlignment.start,
                                  mainAxisSize: MainAxisSize.min,
                                  children: errorMessages.map((message) {
                                    return Text(message.toString());
                                  }).toList(),
                                ),
                                actions: [
                                  TextButton(
                                    onPressed: () {
                                      Navigator.pop(context);
                                    },
                                    child: Text(
                                      "Ok",
                                      style: TextStyle(color: Colors.green),
                                    ),
                                  ),
                                ],
                              );
                            },
                          );
                        } else {
                          // Kesalahan lain yang bukan validasi
                          showDialog(
                            context: context,
                            builder: (ctx) {
                              return AlertDialog(
                                shape: RoundedRectangleBorder(
                                  borderRadius: BorderRadius.circular(12),
                                ),
                                title: Text('Registrasi Gagal'),
                                content: Text('Terjadi kesalahan: $e'),
                                actions: [
                                  TextButton(
                                    onPressed: () {
                                      Navigator.pop(context);
                                    },
                                    child: Text(
                                      "Ok",
                                      style: TextStyle(color: Colors.green),
                                    ),
                                  ),
                                ],
                              );
                            },
                          );
                        }
                      }
                    }
                  },
                  style: ElevatedButton.styleFrom(
                    backgroundColor: Colors.green,
                    shape: RoundedRectangleBorder(
                      borderRadius: BorderRadius.circular(20.0),
                    ),
                    minimumSize: Size(double.infinity, 50.0),
                  ),
                  child: Text('Register'),
                ),

1. try-catch 应该正确放置在哪里？

2. 请帮助我能够根据验证服务器在 Flutter 中显示任何验证错误