一个构建函数返回 null ，相关的导致错误的小部件是：StreamBuilder<EzuserData>
[英]A build function returned null ,The relevant error-causing widget was : StreamBuilder<EzuserData>
问题描述
Hi so I was doing an app like uber but I got an error of this.
嗨，我正在做一个像 uber 这样的应用程序，但我遇到了这个错误。 I'm new in using flutter.我是使用颤振的新手。 Before this, I can run app this normally but suddenly I got this error this morning.在此之前，我可以正常运行应用程序，但今天早上突然出现此错误。 This is my code.这是我的代码。 Can someone help me?有人能帮我吗？
this is the error这是错误
A build function returned null.构建函数返回 null。 The offending widget is: StreamBuilder To return an empty space that causes the building widget to fill available room, return "Container()".有问题的小部件是： StreamBuilder要返回导致建筑小部件填满可用空间的空白空间，请返回“Container()”。 To return an empty space that takes as little room as possible, return "Container(width: 0.0, height: 0.0)".要返回占用尽可能少空间的空白空间，请返回“Container(width: 0.0, height: 0.0)”。
import 'package:ezbin3/Aboutus.dart';
import 'package:ezbin3/SCREENS/home/map.dart';
import 'package:ezbin3/SCREENS/home/map2.dart';
import 'package:ezbin3/SERVICES/auth.dart';
import 'package:ezbin3/activity.dart';
import 'package:ezbin3/models/user.dart';
import 'package:ezbin3/profile.dart';
import 'package:ezbin3/settings.dart';
import 'package:flutter/material.dart';
import 'package:ezbin3/SERVICES/database.dart';
import 'package:provider/provider.dart';
import 'package:ezbin3/models/ezuser.dart';
class Home extends StatelessWidget {
final AuthService _auth = AuthService();
@override
Widget build(BuildContext context) {
final user = Provider.of<User>(context);
return StreamBuilder<EzuserData>(
stream: DatabaseService(uid: user.uid).userData,
builder: (context, snapshot) {
if (snapshot.hasData) {
EzuserData userData = snapshot.data;
return StreamProvider<List<Ezuser>>.value(
value: DatabaseService().userz,
child: Scaffold(
drawer: Drawer(
child: ListView(
children: <Widget>[
DrawerHeader(
decoration: BoxDecoration(
gradient: LinearGradient(colors: <Color>[
Colors.lightGreen,
Colors.green
])),
child: Container(
child: Column(
children: <Widget>[
Material(
borderRadius:
BorderRadius.all(Radius.circular(50.0)),
elevation: 10,
child: Padding(
padding: EdgeInsets.all(8.0),
child: Image.asset(
'image/ezbin2.png',
width: 80,
height: 80,
),
),
),
SizedBox(height: 10),
Text(
userData.name,
style: TextStyle(
color: Colors.white, fontSize: 20.0),
),
],
)),
),
//PROFILE PAGE
Padding(
padding: const EdgeInsets.fromLTRB(8.0, 0, 8.0, 0),
child: Container(
decoration: BoxDecoration(
border: Border(
bottom: BorderSide(
color: Colors.grey.shade400))),
child: InkWell(
splashColor: Colors.lightGreenAccent,
onTap: () => Navigator.push(
context,
MaterialPageRoute(
builder: (context) => ProfilePage())),
child: Container(
height: 50,
child: Row(
mainAxisAlignment:
MainAxisAlignment.spaceBetween,
children: <Widget>[
Row(
children: <Widget>[
Icon(Icons.person),
Padding(
padding:
const EdgeInsets.all(8.0),
child: Text('Profile',
style: TextStyle(
fontSize: 16.0))),
],
),
Icon(Icons.arrow_right)
],
),
)),
)),
//ACTIVITY PAGE
Padding(
padding: const EdgeInsets.fromLTRB(8.0, 0, 8.0, 0),
child: Container(
decoration: BoxDecoration(
border: Border(
bottom: BorderSide(
color: Colors.grey.shade400))),
child: InkWell(
splashColor: Colors.lightGreenAccent,
onTap: () => Navigator.push(
context,
MaterialPageRoute(
builder: (context) => ActivityPage())),
child: Container(
height: 50,
child: Row(
mainAxisAlignment:
MainAxisAlignment.spaceBetween,
children: <Widget>[
Row(
children: <Widget>[
Icon(Icons.description),
Padding(
padding:
const EdgeInsets.all(8.0),
child: Text('Activity',
style: TextStyle(
fontSize: 16.0))),
],
),
Icon(Icons.arrow_right)
],
),
)),
)),
//SETTING PAGE
Padding(
padding: const EdgeInsets.fromLTRB(8.0, 0, 8.0, 0),
child: Container(
decoration: BoxDecoration(
border: Border(
bottom: BorderSide(
color: Colors.grey.shade400))),
child: InkWell(
splashColor: Colors.lightGreenAccent,
onTap: () => Navigator.push(
context,
MaterialPageRoute(
builder: (context) => SettingPage())),
child: Container(
height: 50,
child: Row(
mainAxisAlignment:
MainAxisAlignment.spaceBetween,
children: <Widget>[
Row(
children: <Widget>[
Icon(Icons.settings),
Padding(
padding:
const EdgeInsets.all(8.0),
child: Text('Settings',
style: TextStyle(
fontSize: 16.0))),
],
),
Icon(Icons.arrow_right)
],
),
)),
)),
//ABOUT US PAGE
Padding(
padding: const EdgeInsets.fromLTRB(8.0, 0, 8.0, 0),
child: Container(
decoration: BoxDecoration(
border: Border(
bottom: BorderSide(
color: Colors.grey.shade400))),
child: InkWell(
splashColor: Colors.lightGreenAccent,
onTap: () => Navigator.push(
context,
MaterialPageRoute(
builder: (context) => AboutusPage())),
child: Container(
height: 50,
child: Row(
mainAxisAlignment:
MainAxisAlignment.spaceBetween,
children: <Widget>[
Row(
children: <Widget>[
Icon(Icons.info_outline),
Padding(
padding:
const EdgeInsets.all(8.0),
child: Text('About Us',
style: TextStyle(
fontSize: 16.0))),
],
),
Icon(Icons.arrow_right)
],
),
)),
)),
//LOG OUT
Padding(
padding: const EdgeInsets.fromLTRB(8.0, 0, 8.0, 0),
child: Container(
decoration: BoxDecoration(
border: Border(
bottom: BorderSide(
color: Colors.grey.shade400))),
child: InkWell(
splashColor: Colors.lightGreenAccent,
onTap: () async {
await _auth.signOut();
print('logout');
},
child: Container(
height: 50,
child: Row(
mainAxisAlignment:
MainAxisAlignment.spaceBetween,
children: <Widget>[
Row(
children: <Widget>[
Icon(Icons.lock),
Padding(
padding:
const EdgeInsets.all(8.0),
child: Text('Log Out',
style: TextStyle(
fontSize: 16.0))),
],
),
Icon(Icons.arrow_right)
],
),
)),
))
],
),
),
backgroundColor: Colors.green[50],
appBar: AppBar(
title: Text('EZBIN'),
backgroundColor: Colors.green[400],
elevation: 0.0,
actions: <Widget>[],
),
body: //HomeGoogle(),
MapSample(),
),
);
}
});
}
}
If anything happens please let me know.如果发生任何事情，请告诉我。 Thank you谢谢
1 个解决方案
解决方案1
0 2020-03-04 09:17:33
Let's take a look at the error message我们来看看错误信息
A build function returned null. The offending widget is: StreamBuilder
That means, that somewhere in your program a StreamBuilder (or its build method) is not returning a Widget, but null .这意味着，在您的程序中的某个地方， StreamBuilder（或其构建方法）不返回 Widget，而是返回null 。 Now let's take a look at your code.现在让我们看看你的代码。
return StreamBuilder<EzuserData>(
stream: DatabaseService(uid: user.uid).userData,
builder: (context, snapshot) {
if (snapshot.hasData) {
EzuserData userData = snapshot.data;
return StreamProvider<List<Ezuser>>.value(
...
);
}
});
}
With the error and the simplified code in mind, where could you not return a Widget, but instead no value at all?考虑到错误和简化的代码，您在哪里可以不返回 Widget，而是根本没有值？ Hint: What happens, if snapshot.hasData is not true?提示：如果snapshot.hasData不正确会发生什么？
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