I'm new to flutter. I'm trying to learn about flutter rest api. When I'm trying to post data using fullter api(using http dart package), It shows me this error.

I tried to fix it doing some changes to my code, but I still unable to fix it. Here the code that I trying to execute.

1. Model

    import 'dart:convert';
   
   DataModel dataModelFromJSON(String str) => DataModel.fromJson(jsonDecode(str));
   String dataModelToJson(DataModel data) => json.encode(data.toJson());
   
   class DataModel {
    DataModel(
      {required this.name,
      required this.job,
      required this.id,
      required this.createdAt});
   
      String name;
      String job;
      String id;
      String createdAt;
   
   factory DataModel.fromJson(Map<String, dynamic> json) => DataModel(
      name: json['name'],
      job: json['job'],
      id: json['id'],
      createdAt: json['createdAt']);
   
     Map<String, dynamic> toJson() =>
        {"name": name, "job": job, "id": id, "createdAt": createdAt};
   }
   

2. main.dart

    import 'package:flutter/material.dart';
    import 'package:http/http.dart' as http;
   
    import 'DataModel.dart';
   
     void main() {
      runApp(
      MaterialApp(
      home: MyHomePage(),
    ),
    );
   }
   
   class MyHomePage extends StatefulWidget {
     @override
     _MyHomePageState createState() => _MyHomePageState();
   }
   
   Future<DataModel?> submitData(String name, String job) async {
      var response = await http.post(
      Uri.https('reqres.in', 'api/users'),
      body: {"name": name, "job": job},
      );
      var data = response.body;
      print(data);
   
      if (response.statusCode == 201) {
       String responseString = response.body;
       dataModelFromJSON(responseString);
      } else
       return null;
      }
   
      class _MyHomePageState extends State<MyHomePage> {
         late DataModel _dataModel;
         TextEditingController nameController = TextEditingController();
         TextEditingController jobController = TextEditingController();
   
      @override
      Widget build(BuildContext context) {
        return Scaffold(
         appBar: AppBar(
         title: Center(
          child: Text('HTTP Post'),
          ),
        ),
        body: Container(
          padding: EdgeInsets.all(20.0),
          child: Column(
            children: [
              TextField(
                decoration: InputDecoration(
                    border: OutlineInputBorder(), hintText: 'Name'),
                controller: nameController,
              ),
              SizedBox(height: 20.0),
              TextField(
                decoration: InputDecoration(
                    border: OutlineInputBorder(), hintText: 'Job'),
                controller: jobController,
              ),
              ElevatedButton(
                onPressed: () async {
                  String name = nameController.text;
                  String job = jobController.text;
                  DataModel? data = await submitData(name, job);
                  setState(() {
                    _dataModel = data!;
                  });
                },
                child: Text("Submit"),
              )
            ],
          ),
        ),
      );
    }
   }
   

I appreciate if somebody can help me to fix this issue.

CodePudding user response：

You are not returning data in your function add return here

 return dataModelFromJSON(responseString);

Now your Function will be like this

  Future<DataModel?> submitData(String name, String job) async {
       var response = await http.post(
       Uri.https('reqres.in', 'api/users'),
       body: {"name": name, "job": job},
       );
       var data = response.body;
       print(data);
    
       if (response.statusCode == 201) {
        String responseString = response.body;
       return dataModelFromJSON(responseString);
       } else
        return null;
       }

CodePudding user response：

Remove ! from this line _dataModel = data!; In your data model you have this

    String responseString = response.body;
    dataModelFromJSON(responseString);
   } else
    return null;
   }

Which will return null if the status code of the request is not 201, which it's doing so using ! To do the null check is what's causing the error.