How to handled exception in FutureBuilder Flutter

We have explore how to use Future in Flutter but we did not cover or highlight how to handle error should in case one happens.

This simple flutter code example highlights how to thrown an exception in the event that our FutureBuilder experiences an error.

This flutter example code request data from a remote API.

We will need to add the http library in our project pubspec.yaml

Let’s go ahead and show a simple flutter project that highlights how to handle exception with FutureBuilder.

Create new Flutter Project

In your Visual Studio Code, go to View menu > Command Palette.

In the open dialog, select Flutter. Enter the name of your Flutter project and hit enter key button.

In the lib folder, open the main.dart file and add the code below.

main.dart

import 'package:flutter/material.dart';
import 'futurebuilder_exception.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: ExceptionInFututreBuilder(),
    );
  }
}

Add Dart Http Library

name: food_store
description: A new Flutter project.

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# Read more about versioning at semver.org.
version: 1.0.0+1

environment:
  sdk: ">=2.0.0-dev.68.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2
  http: 0.12.0
  dio: 2.0.22
 
  dev_dependencies:
  flutter_test:
    sdk: flutter

# For information on the generic Dart part of this file, see the
# following page: https://www.dartlang.org/tools/pub/pubspec

# The following section is specific to Flutter.
flutter:
  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true

  assets:
    - assets/images/umbrella.png
    - assets/images/dnut.png
    - assets/star_anim.flr

  fonts:
    - family: AvenirNext
      fonts:
        - asset: assets/fonts/AvenirNextLTPro-Regular.otf

  # To add assets to your application, add an assets section, like this:
  # assets:
  #  - images/a_dot_burr.jpeg
  #  - images/a_dot_ham.jpeg
  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.io/assets-and-images/#resolution-aware.
  # For details regarding adding assets from package dependencies, see
  # https://flutter.io/assets-and-images/#from-packages
  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  #
  # For details regarding fonts from package dependencies,
  # see https://flutter.io/custom-fonts/#from-packages

Create new Dart file in lib folder

Go to the lib folder and create a dart file. Name the file json_array.dart.

Import Flutter Firestore package and dart async also.

Open the newly created dart file and add the code below.

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

import 'package:flutter/material.dart';

class ExceptionInFututreBuilder extends StatelessWidget {
  final String uri =
      'https://jsonplaceholder.typicode.com/users_err'; //intentional error

  Future<String> _errorFuture() async {
    var response = await http.get(uri);

    if (response.statusCode == 200) {
      final items = json.decode(response.body).cast<Map<String, dynamic>>();
      String string = items.first;

      return string;
    } else {
      throw Exception('Failed to load internet');
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Exception in FutureBuilder")),
      body: FutureBuilder<String>(
        future: _errorFuture(),
        builder: (context, snapshot) {
          if (snapshot.hasError) {
            return Center(
              child: Text(
                "ERROR: " + snapshot.error.toString(),
              ),
            );
          }
          return Text(snapshot.data);
        },
      ),
    );
  }
}

You can see from the source code how an exception is thrown when there is an error.

throw Exception('Failed to load internet');

RUN YOUR APP

You can use flutter command to run your app – $ flutter run

If everything goes well, you will see screen similar to the image below in your flutter device.

If you have any question or suggestions kindly use the comment box or you can contact us directly through our contact page below.

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