Error

In my code when open this page then call fetchData() method in initState.fetchData methos call every 15 seconds. initState

Timer? timer;
  Future<List<DataDoctor>>? future;
  @override
  void initState() {
    super.initState();

    timer = Timer.periodic(Duration(seconds: 15), (Timer t) => fetchData());
  }

in fetchData method geting data from API call in the API has these data.

those data should retrieve to backend for now I only retrieve only Boolean value. like as my code this Boolean value I get as doctor_in variable. if doctor_in false then should recall again API and should get data. it should at every 15 seconds until open this page.

data retrieve code

  FutureBuilder<DataDoctor> fetchData() {
    builder:
    (context, snapshot) {
      if (snapshot.hasData) {
        if (snapshot.data!.doctor_in == false) {
          future = client.isDoctorActive();
        }
      } else if (snapshot.hasError) {
        return Text('${snapshot.error}');
      }
    };
  }

model

class DataDoctor {
  String channelName;
  String receiver_name;
  bool doctor_in;

  DataDoctor(
      {required this.channelName,
      required this.receiver_name,
      required this.doctor_in});

  factory DataDoctor.fromJson(Map<String, dynamic> json) {
    return DataDoctor(
      channelName: json['Mobile'] == null ? null : json['Mobile'],
      receiver_name: json['Name'] == null ? null : json['Name'],
      doctor_in: json['Boolean'] == null ? null : json['Boolean'],
    );
  }
}

api call

class ApiServiceDataDoctor {
  final String url =
      'https://tools.learningcontainer.com/sample-json-file.json';
  Future<List<DataDoctor>> isDoctorActive() async {
    Response response = await get(Uri.parse(url));
    if (response.statusCode == 200) {
      Map<String, dynamic> json = jsonDecode(response.body);

      Map<String, dynamic> body = json['dataActive'];
      List<DataDoctor> datas = [DataDoctor.fromJson(body)];
      return datas;
    } else {
      throw ('cannot fetch data');
    }
  }
}

andalso when fetch that boolean value , that should pass to ElevatedButton

if doctor_in == true then ElevatedButton should enable

error ElevatedButton

how to solve this error?

error

CodePudding user response：

Simply make the future nullable or provide some default value. It is throwing exception because the value can be null which will crash the application.

CodePudding user response：

FutureBuilder<DataDoctor> fetchData() {
    builder:
    (context, snapshot) {
      if (snapshot.hasData) {     // ⚠ This if statement is not returning anything, So you are getting error
        if (snapshot.data!.doctor_in == false) {
          future = client.isDoctorActive();
        }
        return Text(`${snapshot.data}`) //