getInstance

Access asynchronously with SharedPreferences.getInstance.

What is getInstance?

To access the SharedPreferences class, you call the static getInstance() method. It returns a Future<SharedPreferences> because it reads from disk. Therefore you need to wait for it with await.

final prefs = await SharedPreferences.getInstance();
// now you can set/get through prefs

async main and ensureInitialized

When using shared_preferences in the main function, make main async and call WidgetsFlutterBinding.ensureInitialized() first. This ensures the Flutter binding is ready; otherwise you get an error in async main.

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final prefs = await SharedPreferences.getInstance();
  runApp(MyApp());
}

Exercise Call getInstance in async main

Make main async, call WidgetsFlutterBinding.ensureInitialized(), get the instance with await getInstance(), and print 'instance ready'.

Show example solution

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

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final prefs = await SharedPreferences.getInstance();
  print('instance ready');
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: Scaffold(body: Center(child: Text('getInstance')));
  }
}

Test yourself

Why is getInstance async?
- Because it draws UI
- Because it compiles code
- Because it reads from disk
- Because it downloads from the internet
Show answer

Because it reads from disk — getInstance prepares the SharedPreferences instance by reading from disk; this takes time, so it returns a Future.

Await getInstance

final prefs = ____ SharedPreferences.getInstance();

Show answer

final prefs = await SharedPreferences.getInstance();

getInstance parts

getInstance

Returns a SharedPreferences instance
await

Waits for the Future result
async

Marks the function as async
Future

Represents the async result

Next lesson: set and get

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