我在应用程序的主/根页面中有一个流构建器。无论何时我在其他地方进行页面导航，这个流构建器都会触发，而与流本身无关。
据我理解，根据这里和这里的说法，当从导航器中弹出/推送页面时，它会触发应用程序的重建，因此流构建器会重新附加并触发。但是这似乎效率低下，是否有一种方法可以防止在推出或推入页面时触发流构建器？
此外，根据日志，在我推送页面时，页面首先被构建和显示，然后流构建器得到触发。但是，尽管日志/调试器清楚地表明已经返回了流构建器的小部件/页面，但流构建器的小部件/页面根本没有显示。它去哪儿了？Flutter框架如何工作？
以下是完整的代码和日志。该代码使用Firebase auth 作为流构建器。
代码：
import 'package:flutter/material.dart';
import 'package:firebase_auth/firebase_auth.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: AppHomePage(),
);
}
}
class AppHomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
final FirebaseAuth auth = FirebaseAuth.instance;
return StreamBuilder<FirebaseUser>(
stream: auth.onAuthStateChanged,
builder: (_, AsyncSnapshot<FirebaseUser> snapshot) {
if (snapshot.connectionState == ConnectionState.active) {
final FirebaseUser user = snapshot.data;
if (user == null) {
debugPrint("User is NULL.");
return SignInPage();
} else {
debugPrint("User exists.");
return MainPage();
}
} else {
debugPrint("In waiting state.");
return Scaffold(
body: Center(
child: CircularProgressIndicator(),
),
);
}
},
);
}
}
class MainPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
debugPrint("Building main page.");
return Scaffold(
body: Center(
child: Text("Welcome to our app!"),
),
);
}
}
class SignInPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
debugPrint("Building sign-in page.");
return Scaffold(
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
FlatButton(
color: Colors.blue,
child: Text('Sign In as Anonymous'),
onPressed: () {
debugPrint("Anonymous");
Navigator.push(
context,
MaterialPageRoute(builder: (context) => MainPage()),
);
},
),
FlatButton(
color: Colors.red,
child: Text('Sign In with Google'),
onPressed: () => debugPrint("Google"),
),
],
),
),
);
}
}
日志，第四行表示按下按钮执行navigator.pop()：
I/flutter (22339): In waiting state.
I/flutter (22339): User is NULL.
I/flutter (22339): Building sign-in page.
I/flutter (22339): Anonymous
I/flutter (22339): Building main page.
I/flutter (22339): User is NULL.
I/flutter (22339): Building sign-in page.