如何防止传递BuildContext？

Question

Currently I get the BuildContext from the build method in HomeScreen , and then I have to pass it down to _gridSliver then down to _storeCard .

How can I write the code so that I don't need to pass the context down?

Maybe I can create a new private StatelessWidget called _StoreCard that will have its own build method and thus its own BuildContext ?

class HomeScreen extends StatelessWidget {
  HomeScreen({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return StoreConnector<AppState, List<MyStore.Store>>(
        converter: (Store<AppState> store) => store.state.home.stores,
        builder: (BuildContext context, List<MyStore.Store> stores) =>
            CustomScrollView(slivers: <Widget>[_gridSliver(stores, context)]));
  }

  Widget _gridSliver(stores, context) {
    return SliverGrid(            
        delegate: SliverChildListDelegate(List<Widget>.from(stores.map(_storeCard, context))));
  }

  Widget _storeCard(MyStore.Store store, BuildContext context) {
    return InkWell(
      onTap: () {
        Navigator.push(
          context,
          MaterialPageRoute(builder: (_) => StoreScreen(storeId: store.id)),
        );
      },
      child: Container(child: Text(store.name))
    );
  }
}

Another instance of this problem is I navigate on a child function.

@override
Widget build(BuildContext context) {
  return Column(
    children: [
      WhiteButton(text: "Login with Facebook", onPressed: _loginWithFacebook),
      WhiteButton(text: "Login with Google", onPressed: _loginWithGoogle),
    ])
  )
}

_loginWithFacebook(context) async {
    ...
    var user = User.fromFacebook(result.accessToken.token, json.decode(graphResponse.body));
    await _login(user, context);
  }
}

_loginWithGoogle(context) async {
    ...
  GoogleSignInAccount googleUser = await _googleSignIn.signIn();
  await _login(User.fromGoogle(googleUser), context);
}

_login(user, context) async {
  var fetchedUser = await MeService.getUser(user);
  if (fetchedUser != null) {
    loginSuccess(fetchedUser);
    Navigator.popUntil(context, ModalRoute.withName(MainRoutes.root));
  } else {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (_) => RegisterScreen(user: user)),
    );
  }
}

Answer 1

To get a new BuildContext , you have two main solutions:

• Extract part of the subtree into a new widget, typically StatelessWidget . And then use it's BuildContext from the build method

• Use Builder widget, which is basically a reusable widget made to obtain a BuildContext :

Example:

 @override
 Widget build(BuildContext context) {
  return Builder(
    builder: (context) {
      // do something with this new context
    },
  );
}

Answer 2

You have to use a Bloc pattern that uses an Inherited Widget, but still you'll have to pass context, but in a more straight forward way. I recommend using this app by Stephen Grider, to figure out how the whole thing works. He explains in his tutorial how to put the whole thing together but I can't link you to that because that would be advertising.

The idea is, you first create a file Bloc.dart that is going to contain your logic, then you create what is called a Provider, in a Provider.dart.

Provider.dart:

class Provider extends InheritedWidget {
final bloc = Bloc();

Provider({Key key, Widget child}) : super(key: key, child: child);

bool updateShouldNotify(_) => true;

static Bloc of(BuildContext context) {
return (context.inheritFromWidgetOfExactType(Provider) as Provider).bloc;
  }
}

In your file that contains the Material App, you wrap the material App with the provider:

Widget build(BuildContext context) {
return Provider(
  child: MaterialApp(

And then you use the provider in every other class down the three of widgets.

class HomeScreen extends StatelessWidget {


@override
Widget build(BuildContext context) {
    final bloc = Provider.of(context); // this is where you insert the provider
    return StoreConnector<AppState, List<MyStore.Store>>(
    converter: (Store<AppState> store) => store.state.home.stores,
    builder: (BuildContext context, List<MyStore.Store> stores) =>
        CustomScrollView(slivers: <Widget>[_gridSliver(stores, context)]));
}

Widget _gridSliver(stores) {
   final bloc = Provider.of(context);
   return SliverGrid(            
    delegate: SliverChildListDelegate(List<Widget>.from(stores.map(_storeCard, context))));
 }

Widget _storeCard(MyStore.Store store) {
  final bloc = Provider.of(context);
  return InkWell(
  onTap: () {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (_) => StoreScreen(storeId: store.id)),
    );
  },
  child: Container(child: Text(store.name))
);


 }
}

I'm a total noob with flutter and take everything with grain of salt, but this is what I would use. Hope it helps.