将两个流合并到一个StreamProvider中 [英] Combine two Streams into one StreamProvider

问题描述

我有两个流:

• Stream< FirebaseUser>FirebaseAuth.instance.onAuthStateChanged
• Stream< User>userService.streamUser(String uid)

我的userService需要将经过身份验证的FirebaseUser的uid作为参数.

My userService requires the uid of the authenticated FirebaseUser as a parameter.

由于我可能需要在应用程序的多个部分中访问streamUser()流，因此我希望它成为项目根目录的提供者.

Since I will probably need to access the streamUser() stream in multiple parts of my app, I would like it to be a provider at the root of my project.

这是我的main.dart的样子:

This is what my main.dart looks like:

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  Widget build(BuildContext context) {
    var auth = FirebaseAuth.instance;
    var userService = new UserService();
    return MultiProvider(
      providers: [
        Provider<UserService>.value(
          value: userService,
        ),
      ],
      child: MaterialApp(
        home: StreamBuilder<FirebaseUser>(
            stream: auth.onAuthStateChanged,
            builder: (context, snapshot) {
              if (!snapshot.hasData) return LoginPage();
              return StreamProvider<User>.value(
                value: userService.streamUser(snapshot.data.uid),
                child: HomePage(),
              );
            }),
      ),
    );
  }
}

问题在于，当我导航到另一个页面时，MaterialApp下面的所有内容都被更改，并且失去了StreamProvider的上下文.

The issue is that when I navigate to a different page, everything below the MaterialApp is changed out and I lose the context with the StreamProvider.

是否可以将StreamProvider添加到MultiProvider provider-list?因为当我尝试时，我还必须为FirebaseUser创建另一个onAuthStateChanged流，并且我不知道如何将它们组合为一个提供程序.

Is there a way to add the StreamProvider to the MultiProvider providers-list? Because when I try, I also have to create another onAuthStateChanged stream for the FirebaseUser and I don't know how to combine them into one Provider.

推荐答案

所以这似乎可以正常工作:

So this seems to work fine:

StreamProvider<User>.value(
  value: auth.onAuthStateChanged.transform(
    FlatMapStreamTransformer<FirebaseUser, User>(
      (firebaseUser) => userService.streamUser(firebaseUser.uid),
    ),
  ),
),

如果在某些情况下有人对此表示怀疑，请告诉我.

If anybody has doubts about this in certain edge cases, please let me know.

感谢 pskink ，以获取有关 查看全文