如何使用Firebase实时数据库数据创建streambuilder和listview(Flutter聊天应用程序)

Question

我正在为我的个人学习项目构建一个flutter聊天应用程序，其中的数据将从Firebase实时数据库中检索。

我从教程中得到了这段代码，但它显示了错误。如何解决这个问题？

StreamBuilder(
stream: dbRef.onValue,
builder: (context, snapshot) {
if (snapshot.hasData) {
print("Error on the way");
messages.clear();
DataSnapshot dataValues = snapshot.data.snapshot; //Error: The getter snapshot is not defined for the type 'Object';
Map<dynamic, dynamic> values = dataValues.value;
values.forEach((key, values) {
messages.add(values);
});
return new ListView.builder(
shrinkWrap: true,
itemCount: messages.length,
itemBuilder: (BuildContext context, int index) {
return Card(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text("Name: " + messages[index]["Text"]),
Text("Time: " + messages[index]["TextTime"]),
],
),
);
},
);
}
},
),

Answer 1

这解决了问题。

StreamBuilder(
stream: _dbRef.onValue,
builder: (context, snapshot) {
List<Message> messageList = [];
if (snapshot.hasData &&
snapshot.data != null &&
(snapshot.data! as DatabaseEvent).snapshot.value !=
null) {
final myMessages = Map<dynamic, dynamic>.from(
(snapshot.data! as DatabaseEvent).snapshot.value
as Map<dynamic, dynamic>); //typecasting
myMessages.forEach((key, value) {
final currentMessage = Map<String, dynamic>.from(value);
messageList.add(Message(
author: currentMessage['Author'],
authorId: currentMessage['Author_ID'],
text: currentMessage['Text'],
time: currentMessage['Time'],));
}); //created a class called message and added all messages in a List of class message
return ListView.builder(
reverse: true,
itemCount: messageList.length,
itemBuilder: (context, index) {
return ChattingDesign(
message: messageList[index],
dbpathToMsgChnl:
'TextChannels/${widget.channels['ChannelName']}/Messages',
showName: shouldShowName(
index,
messageList.length - 1,
messageList,
),
);
},
);
} else {
return Center(
child: Text(
'Say Hi...',
style: TextStyle(
color: Colors.white,
fontSize: 21,
fontWeight: FontWeight.w400),
),
);
}
},
),

Answer 2

根据DataSnapshot类文档，没有名为snapshot的字段

我认为你的代码中有一个拼写错误。

试试这个

StreamBuilder(
stream: dbRef.onValue,
builder: (context, snapshot) {
if (snapshot.hasData) {
print("Error on the way");
messages.clear();
DataSnapshot dataValues = snapshot.data! as DataSnapshot ; //here's the typo;
Map<dynamic, dynamic> values = dataValues.value;
values.forEach((key, values) {
messages.add(values);
});
return new ListView.builder(
shrinkWrap: true,
itemCount: messages.length,
itemBuilder: (BuildContext context, int index) {
return Card(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text("Name: " + messages[index]["Text"]),
Text("Time: " + messages[index]["TextTime"]),
],
),
);
},
);
}
},
),