I have a scenario, I have a login page on my app when a user logins in, the app waits for a response from the api, the api response can come in 2 ways. On way with the data as empty or with a growable list. Eg

{
    "id": "ea6d156a-ac2e-49b1-b006-1cf2c9092224",
    "auth_token": "token",
    "email": "[email protected]",
    "gender": male,
    "fullname": "tester",
    "contactNo": "08056582232",
    "participants": [
        {
            "participantid": "055556666",
            "dateobirth": "1983-10-12T00:00:00",
            "nextofkinname": "Tester",
            "nextofkinemail": "[email protected]",
            "nextofkinphonenumber": "1234567",
            "gender": "female",
            "contactnumber": "8900000",
            "fullname": "Participant Two",
            "userid": "ea6d156a-ac2e-49b1-b006-1cf2c9092224",
            "schedules": [
                {
                    "id": 74436,
                    "followUpStageId": 1,
                    "windowStart": "2022-01-28T00:00:00",
                    "windowEnd": "2022-01-30T00:00:00",
                    "showUp": 0,
                    "showUpDate": null,
                    "vaxDose": 0,
                    
                }                   
                
            ]
        }

or it can come as

{
    "id": "afc7e6ff-878a-418b-9a2f-6f7fe2240085",
    "auth_token": "",
    "email": "[email protected]",
    "gender": "male",
    "fullname": "tester",
    "contactNo": "1234567",
    "participants": []
}

Am storing the values in a shared preference, and using them in different places in the app. I want to check if participants: [] had data if it has data take the user directly to the home screen if is empty the go through the process of adding a participant. How can I check if the size of the participant is zero or not?

this is what I have so far

void getLoggedInStatus() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    isLoggedIn = prefs.getBool('isLoggedIn') ?? false;
    gotData = prefs.getString("participants") ??[]; // get the data from prefs
    print(gotData);
    double data = jsonDecode(gotData);// decode and get size
    print(data);
    var token = prefs.get("auth_token") ?? "";
    var url = Uri.parse(Api.PARTICIPANT_SCHEDULER);

    debugPrint("user is logged in: $isLoggedIn");

    if (isLoggedIn) {
      try {
        // try accessing anything from the server
        var response = await http.get(url,
            headers: {"authorization": "Bearer $token"});
        // token expiration check
        // if 401 is not returned, the token is still valid. skip authentication
        if (response.statusCode != 401) {
          if (data.size !=0) { //this doesnt work, it skips the if statements and does nothing
            WADashboardScreen().launch(context); //go to home screen if not empty
          } else {
          WAAddCredentialScreen().launch(context); //add user details if it is empty
          }
        }
      } on SocketException catch (_) {}
    }
  }

How am saving to the shared prefs

SharedPreferences prefs = await SharedPreferences.getInstance();
var parse = jsonDecode(response.body);
prefs.setBool("isLoggedIn", true);
await prefs.setString('email', parse["email"]);
await prefs.setString('auth_token', parse["auth_token"]);
await prefs.setString('gender', parse["gender"]);
await prefs.setString('participants', (jsonEncode(parse["participants"]))) ;
await prefs.setString('fullname', parse["fullname"]);
await prefs.setString('id', parse["id"]);

Have been scratching my head for a while now, how can I check the size or check if participants has data or not and then proceed to the different screens? Any help is appreciated

CodePudding user response：

      var body=json.decode(response.body);
  if(body["participants"].isEmpty){
    ...
  }

should help u

CodePudding user response：

In await prefs.setString('participants', (jsonEncode(parse["participants"])));

You are doing two wrong things here.

1. You are encoding & parsing json which you are supposed itself a String?

2. You are storing List<dynamic> as a String which is not the optimal way.

You might want to use other packages to store participants. SharedPreference is not optimal for every use case.