构建期间Dart / Flutter中的构建错误

Question

因此，在构建函数中，我加载了用户数据，加载后，我想更改应用程序的主题（调用setState（））。 问题是我无法在构建过程中调用setState，就像状态下面的错误一样。 如何在应用启动时加载用户选择的主题？ 另外，不建议在build函数中加载数据吗？ 它似乎运行良好，但感觉有些粗糙。 谢谢！

Widget build(BuildContext context) {
    //get user object from Firebase
    //once user is loaded, take their chosen color theme and call updateTheme()
}

错误：

This ThemeSwitcherWidget widget cannot be marked as needing to build because the framework is
I/flutter (23889): already in the process of building widgets. A widget can be marked as needing to be built during the
I/flutter (23889): build phase only if one of its ancestors is currently building. This exception is allowed because
I/flutter (23889): the framework builds parent widgets before children, which means a dirty descendant will always be

Answer 1

对于加载数据或进行阻塞调用，您应该使用FutureBuilder或StreamBuilder （我不太了解firebase API，因此无法确定要使用哪个API，但它们非常相似。）一个参数，并以此为基础。 我假设您了解dart的未来API

这是一些示例代码，可以使您有所了解。

StreamBuilder<FirebaseUser>(
  stream: FirebaseAuth.instance.onAuthStateChanged,
  builder: (BuildContext context, snapshot) {
    if (snapshot.connectionState == ConnectionState.waiting) {
      return new SplashScreen();
    } else {
      if (snapshot.hasData) {
        return new MainScreen(firestore: firestore, uuid: snapshot.data.uid);
      }
      return new LoginScreen();
    }
  }
)