Flutter runtime errorFlutter: “Binding has not yet been initialized” / “ServicesBinding.defaultBinaryMessenger was accessed before the binding was initialized”

Why the binding isn’t ready, and the fix

1. 01

   A plugin call in main() before runApp

   “You only need to call this method if you need the binding to be initialized before calling runApp.” Flutter, WidgetsFlutterBinding.ensureInitialized

   Firebase.initializeApp, SharedPreferences.getInstance, path_provider and SystemChrome.setPreferredOrientations all need the binding. Create it first.

   Future<void> main() async {
     WidgetsFlutterBinding.ensureInitialized();
     await Firebase.initializeApp(
       options: DefaultFirebaseOptions.currentPlatform,
     );
     final prefs = await SharedPreferences.getInstance();
     runApp(MyApp(prefs: prefs));
   }

2. 02

   A unit test that touches a plugin

   Plain test() blocks don’t create a binding; testWidgets does. Create the test binding at the top of main, and mock the plugin (for example SharedPreferences.setMockInitialValues) since there is no platform side in tests.

   void main() {
     TestWidgetsFlutterBinding.ensureInitialized();
     test('loads settings', () async {
       SharedPreferences.setMockInitialValues({});
       // ...
     });
   }

3. 03

   A plugin call in a background isolate

   “A BinaryMessenger for use on background (non-root) isolates.” Flutter, BackgroundIsolateBinaryMessenger

   Isolate.run or compute starts a new isolate with no binding. Pass the root isolate token in and set up the background messenger before any plugin call. Not every plugin works off the main isolate.

   final token = RootIsolateToken.instance!;
   await Isolate.run(() async {
     BackgroundIsolateBinaryMessenger.ensureInitialized(token);
     final dir = await getApplicationDocumentsDirectory();
     // ...
   });

Checked against the vendor’s docs on November 8, 2026: Flutter API: WidgetsFlutterBinding.ensureInitialized; Flutter API: BackgroundIsolateBinaryMessenger.

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Related: Flutter MissingPluginException · Flutter “Null check operator used on a null value” · Flutter LateInitializationError · Flutter “type 'Null' is not a subtype of type 'String'”