CODEWITHSUNDEEP
flutterflutter-change-notifier
buttonsrtoys
buttonsrtoys

Reputation: 2771

Provider.of<> returning null with ChangeNotifierProxyProvider?

In my test code below I have a flag that determines whether to use a ChangeNotifierProvider or a ChangeNotifierProxyProvider. When I press the RaisedButton both approaches properly display my GroupEditorPage.

const isUsingChangeNotifierProxyProvider = true;

class GroupsPage extends StatelessWidget {
  showGroupEditor(BuildContext context) {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (_) {
        return isUsingChangeNotifierProxyProvider
            ? ChangeNotifierProxyProvider<CloudServicesProvider,
                GroupEditorProvider>(
                create: (_) => GroupEditorProvider(),
                update: (_, cloudServicesProvider, groupEditorProvider) =>
                    groupEditorProvider.update(cloudServicesProvider),
                child: GroupEditorPage(),
              )
            : ChangeNotifierProvider<GroupEditorProvider>(
                create: (_) => GroupEditorProvider(),
                child: GroupEditorPage(),
              );
      }),
    );
  }

  @override
  Widget build(BuildContext context) {
    return SliversPage(
      text: 'Testing',
      sliverList: SliverList(
        delegate: SliverChildBuilderDelegate(
          (BuildContext context, int index) {
            return RaisedButton(
              child: Text('+Create Group'),
              onPressed: () => showGroupEditor(context),
            );
          },
          childCount: 1,
        ),
      ),
    );
  }
}

But Provider.of only returns my GroupEditorProvider instance when ChangeNotifierProvider is used. When Change ChangeNotifierProxyProvider is used, groupEditorProvider below is null.

class GroupEditorPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final groupEditorProvider = Provider.of<GroupEditorProvider>(context);

I've been using Provider for some time but am new to ChangeNotifierProxyProvider so likely not understanding something fundamental.

Upvotes: 1

Views: 182

Answers (1)

buttonsrtoys
buttonsrtoys

Reputation: 2771

Turns out I wasn't returning the provider instance from my GroupEditorProvider.update function:

  update(CloudServicesProvider cloudServicesProvider) {
    if (_cloudServicesProvider == null) {
      this._cloudServicesProvider = cloudServicesProvider;
    }
    return this; // <--- was missing
  }

Should Flutter have thrown an exception for this? I'll post to github if so.

Upvotes: 2

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