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Search as we type

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A real world example could be to use FutureProvider to implement a searchbar.

Implementing a "search as we type" can seem daunting at first when using conventional means.
There are lots of moving parts, such as:

  • handling errors.
  • debouncing the user input to avoid making network requests on every keystroke.
  • cancelling previously pending network requests when the search field changes.

But the combination of FutureProvider and the power of [ref.watch] can significantly simplify this task.

A common pattern wanting to perform an asynchronous requests is to split it into multiple providers:

  • a [StateNotifierProvider] or StateProvider for the parameters of your request (or alternatively use [family])
  • a FutureProvider, which will do the request by reading the parameters from the other providers/[family].

The first step would be to store the user input somewhere. For this example, we will use StateProvider (as the search state is only a single String):

final searchInputProvider = StateProvider<String>((ref) => '');

We can then connect this provider to a [TextField] by doing:

Consumer(
  builder: (context, ref, child) {
    return TextField(
      onChanged: (value) => ref.read(searchInputProvider.notifier).state = value,
    );
  },
)

Then, we can create our FutureProvider which will take care of the request:

final searchProvider = FutureProvider<


<!--
// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

final searchFieldProvider = StateProvider<String>((ref) => '');
final questionsProvider = FutureProvider<List>((ref) async {
  final client = http.Client();
  ref.onDispose(client.close);

  final search = ref.watch(searchFieldProvider);

  Uri uri;

  if (search.isEmpty) {
    uri = Uri.parse(
      'https://api.stackexchange.com/2.3/questions?order=desc&sort=activity&site=stackoverflow',
    );
  } else {
    final encodedQuery = Uri.encodeComponent(search);
    uri = Uri.parse(
      'https://api.stackexchange.com/2.3/search?order=desc&sort=activity&intitle=$encodedQuery&site=stackoverflow',
    );
  }

  final response = await client.get(uri);
  final questions = jsonDecode(response.body);

  return questions['items'].map((question) => question['title']).toList();
});

void main() => runApp(const ProviderScope(child: MyApp()));

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(home: MyHomePage());
  }
}

class MyHomePage extends ConsumerWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final questions = ref.watch(questionsProvider);

    return Scaffold(
      appBar: AppBar(title: const Text('Questions')),
      body: Column(
        children: [
          TextField(
            onChanged: (value) =>
                ref.read(searchFieldProvider.notifier).state = value,
          ),
          Expanded(
            child: switch (questions) {
              AsyncData(:final value) => ListView.builder(
                  itemCount: value.length,
                  itemBuilder: (context, index) {
                    final question = value[index];

                    return ListTile(
                      title: Text(
                        question.toString(),
                      ),
                    );
                  },
                );,
              AsyncError(:final error) => Center(child: Text('Error $error')),
              _ => const Center(child: CircularProgressIndicator()),
            },
          ),
        ],
      ),
    );
  }
}