在首次启动时保存并检索json对象

Question

我有一个问题。应用启动后，我需要在应用启动时保存和检索json对象。因此，我提出了一个简单的get请求，该请求从我的响应中返回用户详细信息，并将其另存为具有共享首选项的对象。因此，保存后，我会立即反序列化，以便我可以随时使用。问题在于它在第一次启动时不起作用。仅在第二次启动后才能检索保存的对象。我已经尝试了很多故障排除方法，但没有真正的成功。

UserClass

class User {
 final String first_name;
 final String email;
 final String last_name;
 final String country;
 final String gender;
 final String phone;
 final String profile_image;
 final String created_at;
 final String updated_at;
 final String category;
 final String industry;
 final String bio_interest;
 final String fav_quote;
 final String current_job;
 final String state_of_origin;
  int id = 0;

  User(this.first_name, this.email, this.last_name, this.country, this.gender, this.phone,
      this.profile_image, this.created_at, this.updated_at, this.category, this.industry, this.bio_interest,
      this.fav_quote, this.current_job, this.state_of_origin, this.id);

  Map<String, dynamic> toJson() => {
        'first_name': first_name,
        'email': email,
        'last_name': last_name,
        'country': country,
        'gender': gender,
        'phone': phone,
        'profile_image': profile_image,
        'created_at': created_at,
        'updated_at': updated_at,
        'category': category,
        'industry': industry,
        'bio_interest': bio_interest,
        'fav_quote': fav_quote,
        'current_job': current_job,
        'state_of_origin': state_of_origin,
        'id': id,
      };

  User.fromJson(Map<String, dynamic> json):
        first_name = json['first_name'],
        email = json['email'],
        last_name = json['last_name'],
        country = json['country'],
        gender = json['gender'],
        phone = json['phone'],
        profile_image = json['profile_image'],
        created_at = json['created_at'],
        updated_at = json['updated_at'],
        category = json['category'],
        industry = json['industry'],
        bio_interest = json['bio_interest'],
        fav_quote = json['fav_quote'],
        current_job = json['current_job'],
        state_of_origin = json['state_of_origin'],
        id = json['id'];
}

NetworkClass

class Network(){
static Future fetch(var authToken, var endPoint) async {
    var uri = host + endPoint;
    try {
      final response = await http.get(
        uri,
        headers: {'Accept': 'application/json', 'Content-Type': 'application/json','Authorization': authToken, },
      );

      final responseJson = json.decode(response.body);
      SharedPref sharedPref = SharedPref();
      sharedPref.save("user", responseJson);
      return responseJson;
    } catch (exception) {
      print(exception);
      if (exception.toString().contains('SocketException')) {
        return 'NetworkError';
      } else {
        return null;
      }
    }
  }
}

MainScreen

 String _firstName = "";
  String _lastName = "";
  String _nationality = "";
  String _fav_quote = "";
  String _industry = "";
  String names = "";
  String _profile_image = "";
  String _appBarText = "Welcome";

  @override
  void initState() {
    super.initState();
    checkLoginState();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
  }

  Future checkLoginState() async {
    sharedPreferences = await SharedPreferences.getInstance();
    if (sharedPreferences.getString("token") == null) {
      Navigator.of(context).pushAndRemoveUntil(
          MaterialPageRoute(builder: (BuildContext context) => LoginScreen()),
          (Route<dynamic> route) => false);
    } else {
      Network.fetch("Bearer " + sharedPreferences.getString("token"),
          AuthUtils.endPointProfile);
      //read value from shared preference
      User user = User.fromJson(await sharedPref.read("user"));
     //that line only works from second launch
      setState(() {
        //these variables dont get set on first launch
        _appBarText = "Welcome, " + user.first_name;
        id = user.id;
        _firstName = user.first_name;
        _lastName = user.last_name;
        _nationality = user.country;
        _fav_quote = user.fav_quote;
        _industry = user.industry;
        _profile_image = user.profile_image;
        names = _firstName + " " + _lastName;
      });
      try {
      } catch (Excepetion) {
        // do something
      }
    }
  }

}

Answer 1

我不确定您如何在SharedPref类中存储数据，但是要实现您提到的功能，可以按照以下步骤操作：

1. 从服务器获取数据后，您可以将数据作为字符串存储到SharedPreferences中，如下所示：>

   final SharedPreferences _prefs = await SharedPreferences.getInstance();
   
   await _prefs.setString("users", response.body); 
   
   //  your response.body should be a `String`, 
   // if it is not `String` or it is a JSON you can convert it by 
   // json.encode(response.body);
   

2. [如果需要，您可以从SharedPreferences的任何地方检索数据

 final SharePreferences _prefs = await SharedPreferences.getInstance();
 String _userString = _prefs.getString("user");

 final User _user = User.fromMap(json.decode(_userString));

Answer 2

在获取数据时使用await关键字对我有用。