I am trying to perform user login with my flutter app but then I keep getting data != null error and that a Text Widget must have a non-null string.

Upon further debugging, I realized the response['message'] is printing a null value so I implement a condition to check if it's not null before proceeding but yet still it keeps giving me the same error.

When I use response['message'].toString(), it still gives the same error.

this is the full error being thrown 'data != null': A non-null String must be provided to a Text widget.

the issue seems to be from the response['message'] but I just can't seem to find ways to solve it

This is Auth controller class

  class AuthController extends GetxController {
  AuthService authService = AuthService();
  ProjectApis projectApis = ProjectApis();

  String name = '';
  String email = '';
  String password = '';
  String confirmPassword = '';
  var isPasswordHidden = true.obs;

  
  Future loginUser(BuildContext context) async {
    buildLoader(context, message: 'Loading...');

    http.Response response = await authService.signInUser(
      email,
      password,
    );
    if (response.statusCode == 200) {
      Map<String, dynamic> responseData = json.decode(response.body);
      debugPrint(responseData.toString());
      debugPrint(responseData['message']);
      if (responseData["status"] == true) {
        User user = User.fromJson(responseData);

        UserPreferences().setUser(user);
        Navigator.pop(context);
        Get.offAll(() => BottomNavigation());
        return;
      } else {
        Navigator.pop(context);
        ScaffoldMessenger.of(context).showSnackBar(SnackBar(
          content: Text(responseData['message']),
        ));

        return;
      }
    } else {
      Navigator.pop(context);

      showErrorDialog(context, message: "Server Error");
      return;
    }
  }
}

This is the sign in function

Future<http.Response> signInUser(
    String email,
    String password,
  ) async {
    Map data = {
      'email': email,
      'password': password,
    };
    var body = json.encode(data);
    var url = Uri.parse(projectApis.loginUrl);

    var response = await client.post(
      url,
      body: body,
      headers: projectApis.headers,
    );
    return response;
  }

This is the User model class

User userFromJson(String str) => User.fromJson(json.decode(str));

String userToJson(User data) => json.encode(data.toJson());

class User {
  User({
    this.id,
    this.name,
    this.email,
    this.password,
    this.passwordConfirm,
    this.token,
  });

  int? id;
  String? name;
  String? email;
  String? password;
  String? passwordConfirm;
  String? token;

  String applicationDirPath = "";

  factory User.fromJson(Map<String, dynamic> json) => User(
        id: json["id"],
        name: json["name"],
        email: json["email"],
        password: json["password"],
        passwordConfirm: json["passwordConfirm"],
        token: json["token"],
      );

  Map<String, dynamic> toJson() => {
        "id": id,
        "name": name,
        "email": email,
        "password": password,
        "passwordConfirm": passwordConfirm,
        "token": token,
      };
}

CodePudding user response：

Use null-operator like here

response['message'] ?? ''

If left side was null the right side will assing But you can use this just if you are sure this happen because of this line

• read in medium

CodePudding user response：

I think problem is with the Text(responseData['message']), line.

Dart can't be shure that me message key exist on responseData Map. So Text(responseData['message']), can be null which is bad for null safety.

Just do:

String message = responseData['message'] ?? '';

The ?? operator will return an empty string in case ResponseData['message'] is null.

Then replace in your Text widget:

Text(message),

CodePudding user response：

Text widget doesn't accept nullable String, and reading map can provide null value. You can provide default value on null case like

Text(myMap["key"]??"defaultValue")

And for perser you can do

 if (responseData["status"]  != null && responseData["status"]==true ) {