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Flutter – Updating Data on the Internet
  • Last Updated : 17 Sep, 2020

In today’s world, most applications heavily rely on fetching and updating information from the servers through the internet. In Flutter, such services are provided by the http package. In this article, we will explore the same.

To update the data on the Internet follow the below steps:

  1. Import the http package
  2. Update data t using the http package
  3. Convert the response into custom Dart object
  4. Get the data from the internet.
  5. Update and display the response on screen

Importing The http Package:

To install the http package use the below command in your command prompt:

pub get

Or, if you’re using the flutter cmd use the below command:

flutter pub get



After the installation add the dependency to the pubsec.yml file as shown below:

import 'package:http/http.dart' as http;

Update Data over the Internet:

Use the http.put() method to update the title of the Album in JSONPlaceholder as shown below:

Dart




Future<http.Response> updateAlbum(String title) {
  return http.put(
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
    body: jsonEncode(<String, String>{
      'title': title,
    }),
  );
}

Converting the Response:

Though making a network request is no big deal, working with the raw response data can be inconvenient. To make your life easier, converting the raw data (ie, http.response) into dart object. Here we will create an Album class that contains the JSON data as shown below:

Dart




class Album {
  final int id;
  final String title;
  
  Album({this.id, this.title});
  
  factory Album.fromJson(Map<String, dynamic> json) {
    return Album(
      id: json['id'],
      title: json['title'],
    );
  }
}

Convert http.Respone to an Album:

Now, follow the below steps to update the fetchAlbum() function to return a Future<Album>:

  1. Use the dart: convert package to convert the response body into a JSON Map.
  2. Use the fromJSON() factory method to convert JSON Map into Album if the server returns an OK response with a status code of 200.
  3. Throw an exception if the server doesn’t return an OK response with a status code of 200.

Dart




Future<Album> updateAlbum(String title) async {
  final http.Response response = await http.put(
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
    body: jsonEncode(<String, String>{
      'title': title,
    }),
  );
  // Dispatch action depending upon
  // the server response
  if (response.statusCode == 200) {
    return Album.fromJson(json.decode(response.body));
  } else {
    throw Exception('Failed to load album');
  }
}

Fetching the Data:

Now use the fetch() method to fetch the data as shown below:



Dart




Future<Album> fetchAlbum() async {
  final response =
      await http.get('https://jsonplaceholder.typicode.com/albums/1');
  
  if (response.statusCode == 200) {
    return Album.fromJson(json.decode(response.body));
  } else {
    throw Exception('Failed to load album');
  }
}

Update the existing Data through user input:

Now create a TextField for the user to enter a title and a RaisedButton to send data to the server. Also, define a TextEditingController to read the user input from a TextField as shown below:

Dart




Column(
  mainAxisAlignment: MainAxisAlignment.center,
  children: <Widget>[
    Padding(
      padding: const EdgeInsets.all(8.0),
      child: TextField(
        controller: _controller,
        decoration: InputDecoration(hintText: 'Enter Title'),
      ),
    ),
    RaisedButton(
      child: Text('Update Data'),
      onPressed: () {
        setState(() {
          _futureAlbum = updateAlbum(_controller.text);
        });
      },
    ),
  ],
)

Displaying the Data:

Use the FlutterBuilder widget to display the data on the screen as shown below:

Dart




FutureBuilder<Album>(
  future: _futureAlbum,
  builder: (context, snapshot) {
    if (snapshot.hasData) {
      return Text(snapshot.data.title);
    } else if (snapshot.hasError) {
      return Text("${snapshot.error}");
    }
  
    return CircularProgressIndicator();
  },
)

Complete Source Code:

Dart




import 'dart:async';
import 'dart:convert';
  
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
  
Future<Album> fetchAlbum() async {
  final response =
  
  // Dispatch action depending upon
  //the server response
  if (response.statusCode == 200) {
    return Album.fromJson(json.decode(response.body));
  } else {
    throw Exception('Failed to load album');
  }
}
  
Future<Album> updateAlbum(String title) async {
  final http.Response response = await http.put(
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
    body: jsonEncode(<String, String>{
      'title': title,
    }),
  );
  // parsing JSOn or throwing an exception
  if (response.statusCode == 200) {
    return Album.fromJson(json.decode(response.body));
  } else {
    throw Exception('Failed to update album.');
  }
}
  
class Album {
  final int id;
  final String title;
  
  Album({this.id, this.title});
  
  factory Album.fromJson(Map<String, dynamic> json) {
    return Album(
      id: json['id'],
      title: json['title'],
    );
  }
}
  
void main() {
  runApp(MyApp());
}
  
class MyApp extends StatefulWidget {
  MyApp({Key key}) : super(key: key);
  
  @override
  _MyAppState createState() {
    return _MyAppState();
  }
}
  
class _MyAppState extends State<MyApp> {
  final TextEditingController _controller = TextEditingController();
  Future<Album> _futureAlbum;
  
  @override
  void initState() {
    super.initState();
    _futureAlbum = fetchAlbum();
  }
  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Update Data Example',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: Text('GeeksForGeeks'),
          backgroundColor: Colors.green,
        ),
        body: Container(
          alignment: Alignment.center,
          padding: const EdgeInsets.all(8.0),
          child: FutureBuilder<Album>(
            future: _futureAlbum,
            builder: (context, snapshot) {
              if (snapshot.connectionState == ConnectionState.done) {
                if (snapshot.hasData) {
                  return Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      Text(snapshot.data.title),
                      TextField(
                        controller: _controller,
                        decoration: InputDecoration(hintText: 'Enter Title'),
                      ),
                      RaisedButton(
                        child: Text('Update Data'),
                        onPressed: () {
                          setState(() {
                            _futureAlbum = updateAlbum(_controller.text);
                          });
                        },
                      ),
                    ],
                  );
                } else if (snapshot.hasError) {
                  return Text("${snapshot.error}");
                }
              }
              return CircularProgressIndicator();
            },
          ),
        ),
      ),
    );
  }
}

Output:

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