谁能告诉我为什么我收到此错误？我正在构建一个聊天应用程序，可以在其中显示消息时间和消息文本。但是，当我发送一条消息时，它会向我显示错误：
════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following NoSuchMethodError was thrown building StreamBuilder<QuerySnapshot>(dirty, state: _StreamBuilderBaseState<QuerySnapshot, AsyncSnapshot<QuerySnapshot>>#63fa3):
The getter 'seconds' was called on null.
Receiver: null
Tried calling: seconds
The relevant error-causing widget was:
StreamBuilder<QuerySnapshot> file:///J:/My%20Documents/flutter/flash-chat-flutter/lib/screens/chat_screen.dart:107:12
When the exception was thrown, this was the stack:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
#1 MessageStream.build.<anonymous closure> (package:flash_chat/screens/chat_screen.dart:127:28)
#2 StreamBuilder.build (package:flutter/src/widgets/async.dart:514:81)
#3 _StreamBuilderBaseState.build (package:flutter/src/widgets/async.dart:129:48)
#4 StatefulElement.build (package:flutter/src/widgets/framework.dart:4681:28)
...
════════════════════════════════════════════════════════════════════════════════════════════════════
════════ Exception caught by rendering library ═════════════════════════════════════════════════════
A RenderFlex overflowed by 99729 pixels on the bottom.
The relevant error-causing widget was:
Column file:///J:/My%20Documents/flutter/flash-chat-flutter/lib/screens/chat_screen.dart:57:16
════════════════════════════════════════════════════════════════════════════════════════════════════
这是我的代码
import 'package:flutter/material.dart';
import 'package:flash_chat/constants.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:intl/intl.dart';
final _fireStore = Firestore.instance;
final _auth = FirebaseAuth.instance;
FirebaseUser loggedInUser;
class ChatScreen extends StatefulWidget {
static String id = 'chat_screen';
@override
_ChatScreenState createState() => _ChatScreenState();
}
class _ChatScreenState extends State<ChatScreen> {
final messageTextController = TextEditingController();
String messageText;
@override
void initState() {
super.initState();
getCurrentUser();
}
void getCurrentUser() async {
try {
final user = await _auth.currentUser();
if (user != null) {
loggedInUser = user;
print(loggedInUser.email);
}
} catch (e) {
print(e);
}
}
@override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.white,
appBar: AppBar(
leading: null,
actions: <Widget>[
IconButton(
icon: Icon(Icons.close),
onPressed: () {
_auth.signOut();
Navigator.pop(context);
}),
],
title: Text('⚡️Chat'),
backgroundColor: Colors.lightBlueAccent,
),
body: SafeArea(
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
MessageStream(),
Container(
decoration: kMessageContainerDecoration,
child: Row(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Expanded(
child: TextField(
controller: messageTextController,
style: TextStyle(
color: Colors.black,
),
onChanged: (value) {
messageText = value;
},
decoration: kMessageTextFieldDecoration,
),
),
FlatButton(
onPressed: () async {
messageTextController.clear();
final fieldValue = FieldValue.serverTimestamp();
await _fireStore.collection('messages').add({
"sender": loggedInUser.email,
"text": messageText,
"messageTime": fieldValue,
});
},
child: Text(
'Send',
style: kSendButtonTextStyle,
),
),
],
),
),
],
),
),
);
}
}
class MessageStream extends StatelessWidget {
@override
Widget build(BuildContext context) {
return StreamBuilder<QuerySnapshot>(
stream: _fireStore
.collection('messages')
.orderBy('messageTime', descending: false)
.snapshots(),
builder: (context, snapshot) {
var timeDate;
if (!snapshot.hasData) {
return Center(
child: CircularProgressIndicator(
backgroundColor: Colors.lightBlueAccent,
),
);
} else {
final messages = snapshot.data.documents.reversed;
List<MessageBubble> messageBubbles = [];
for (var message in messages) {
final messageText = message.data['text'];
final sender = message.data['sender'];
Timestamp serverTime = message.data['messageTime'];
if (serverTime.seconds != null && serverTime.nanoseconds != null) {
timeDate = Timestamp(serverTime.seconds, serverTime.nanoseconds)
.toDate();
}
var time = DateFormat.jm().format(timeDate);
final currentUser = loggedInUser.email;
final messageBubble = MessageBubble(
message: messageText,
sender: sender,
isMe: currentUser == sender,
messageTime: time.toString(),
);
messageBubbles.add(messageBubble);
}
return Expanded(
child: ListView(
reverse: true,
children: messageBubbles,
),
);
}
},
);
}
}
class MessageBubble extends StatelessWidget {
MessageBubble({this.sender, this.message, this.isMe, this.messageTime});
String message;
String sender;
bool isMe;
String messageTime;
@override
Widget build(BuildContext context) {
return Column(
crossAxisAlignment:
isMe ? CrossAxisAlignment.end : CrossAxisAlignment.start,
children: <Widget>[
Padding(
padding: isMe
? EdgeInsets.only(
right: 20,
)
: EdgeInsets.only(
left: 20,
),
child: Text(
sender,
style: TextStyle(color: Colors.black45),
),
),
Padding(
padding: EdgeInsets.symmetric(
horizontal: 10,
vertical: 5,
),
child: Material(
borderRadius: isMe
? BorderRadius.only(
topLeft: Radius.circular(20),
bottomLeft: Radius.circular(20),
bottomRight: Radius.circular(20),
)
: BorderRadius.only(
topRight: Radius.circular(20),
bottomLeft: Radius.circular(20),
bottomRight: Radius.circular(20),
),
elevation: 5,
color: isMe ? Colors.lightBlueAccent : Colors.white,
child: Padding(
padding: EdgeInsets.symmetric(
horizontal: 15,
vertical: 15,
),
child: Column(
children: <Widget>[
Text(
message,
style: TextStyle(
fontSize: 15,
),
),
Text(
messageTime,
style: TextStyle(
fontSize: 10,
color: Colors.black54,
),
),
],
),
),
),
),
SizedBox(
height: 10,
),
],
);
}
}
答案 0 :(得分：1)
问题是有很多消息，但是在聊天屏幕中包含它们的Column无法滚动，请在Column中将SingleChildScrollView包装在聊天屏幕中：
@override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.white,
appBar: AppBar(
leading: null,
actions: <Widget>[
IconButton(
icon: Icon(Icons.close),
onPressed: () {
_auth.signOut();
Navigator.pop(context);
}),
],
title: Text('⚡️Chat'),
backgroundColor: Colors.lightBlueAccent,
),
body: SafeArea(
child: SingleChildScrollView( // this is new
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
MessageStream(),
...