Flutter：无法从 showModalBottomSheet 访问 Provider

Question

I can't access a provider defined above a Scaffold from showModalBottomSheet in the FloatingActionButton.

I've defined a HomePage like so:

class HomePage extends StatelessWidget {
 @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (_) => MyProvider(),
      builder: (context, _) {
        return Scaffold(
          body: Consumer<MyProvider>(
             builder: (context, provider, _) {
               return Text(provider.mytext); // this works fine
             }
          ),
          floatingActionButton: MyFAB(), // here is the problem
        );
      }
    )
  }
}

And this is MyFAB:

class MyFAB extends StatefulWidget {
  @override
  _MyFABState createState() => _MyFABState();
}

class _MyFABState extends State<MyFAB> {
  @override
  Widget build(BuildContext context) {
    return FloatingActionButton(
      ...
      onPressed: () => show(),
    );
  }
  
  void show() {
    showModalBottomSheet(
      ...
      context: context,
      builder: (BuildContext context) {
        return Wrap(
          children: [
            ...
            FlatButton(
              onPressed: Provider.of<MyProvider>(context, listen: false).doSomething(); //Can't do this
              Navigator.pop(context);
            )
          ],
        );
      }
    );
  }
}

Error: Could not find the correct Provider<MyProvider above this BottomSheet Widget.

Answer 1

Fixed by placing the provider above MaterialApp , as described here .

Bottom sheets are created at the root of the material app. If a prodiver is declared below the material app, a bottom sheet cannot access it because the provider is not an ancestor of the bottom sheet in the widget tree.

The screenshot below shows a widget tree: the whole app is inside Wrapper and the bottom sheet is not created inside Wrapper . It is created as another child of MaterialApp (with a root element Container in this case).

For your case:

// main.dart
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (_) => MyProvider(),
      builder: (context, _) {
        return MaterialApp(
          home: HomePage(),
        );
      },
    );
  }
}

// home_page.dart
class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: MyFAB()
    );
  }
}

Answer 2

This is caused by passing it the wrong context. Wrap your FAB to a Builder widget and pass it as builder property. This will take a new context and pass it to showModalBottomSheet. Also, you can do onPressed: show , it's more concise.

 class HomePage extends StatelessWidget {
 @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (_) => MyProvider(),
      builder: (context, _) {
        return Scaffold(
          body: Consumer<MyProvider>(
             builder: (context, provider, _) {
               return Text(provider.mytext); // this works fine
             }
          ),
          floatingActionButton: MyFAB(context), // here is the problem
        );
      }
    )
  }
}


class MyFAB extends StatefulWidget {
  @override
  _MyFABState createState() => _MyFABState();
}

class _MyFABState extends State<MyFAB> {
  @override
  Widget build(BuildContext context) {
    return FloatingActionButton(
      ...
      onPressed: (context) => show(context),
    );
  }
  
  void show(ctx) {
    showModalBottomSheet(
      ...
      context: ctx,
      builder: (BuildContext context) {
        return Wrap(
          children: [
            ...
            FlatButton(
              onPressed: () {
              Provider.of<MyProvider>(ctx, listen: false).doSomething(); //Can't do this
              Navigator.pop(ctx)
              };
            )
          ],
        );
      }
    );
  }
}

Answer 3

SOLUTION

HomePage:

class HomePage extends StatelessWidget {
 @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (_) => MyProvider(),
      builder: (context, _) {
        return Scaffold(
          body: Consumer<MyProvider>(
             builder: (context, provider, _) {
               return Text(provider.mytext); // this works fine
             }
          ),
          floatingActionButton: MyFAB(context), // here is the problem
        );
      }
    )
  }
}

MyFAB:

class MyFAB extends StatefulWidget {
final BuildContext ctx;

MyFAB(this.ctx)

  @override
  _MyFABState createState() => _MyFABState();
}

class _MyFABState extends State<MyFAB> {
  @override
  Widget build(BuildContext context) {
    return FloatingActionButton(
      ...
      onPressed: () => show(),
    );
  }
  
  void show() {
    showModalBottomSheet(
      ...
      context: context,
      builder: (BuildContext context) {
        return Wrap(
          children: [
            ...
            FlatButton(
              onPressed: Provider.of<MyProvider>(widget.ctx, listen: false).doSomething(); //Can't do this
              Navigator.pop(context);
            )
          ],
        );
      }
    );
  }
}