参考StreamBuilder官方文档：https://api.flutter.dev/flutter/widgets/StreamBuilder-class.html#widgets.StreamBuilder.1
StreamBuilder builder方法里面有一个AsyncSnapshot值，里面不仅有Stream的数据，还有状态和错误。在您的 builder 方法中，检查 snapshot.hasError 和 snapshot.state。连接有4种状态：
enum ConnectionState {
/// Not currently connected to any asynchronous computation.
///
/// For example, a [FutureBuilder] whose [FutureBuilder.future] is null.
none,
/// Connected to an asynchronous computation and awaiting interaction.
waiting,
/// Connected to an active asynchronous computation.
///
/// For example, a [Stream] that has returned at least one value, but is not
/// yet done.
active,
/// Connected to a terminated asynchronous computation.
done,
}
您的“延迟”是由于这些状态之间的切换造成的，因此理想情况下，您需要为每个状态指定返回。请参阅完整示例，取自文档：
return Scaffold(
body: ListView(
children: <Widget>[
select(), // decide buyOrSell
StreamBuilder(
stream: buyOrSell == "buy"
? FirebaseFirestore.instance
.collection("buy")
.doc(widget.profileId)
.collection("barter")
.orderBy('timestamp', descending: true)
.snapshots()
: FirebaseFirestore.instance
.collection("sell")
.doc(widget.profileId)
.collection("barter")
.orderBy('timestamp', descending: true)
.snapshots(),
builder: (BuildContext context, AsyncSnapshot<dynamic> snapshot) {
List<Widget> children;
if (snapshot.hasError) {
children = <Widget>[
const Icon(
Icons.error_outline,
color: Colors.red,
size: 60,
),
Padding(
padding: const EdgeInsets.only(top: 16),
child: Text('Error: ${snapshot.error}'),
),
Padding(
padding: const EdgeInsets.only(top: 8),
child: Text('Stack trace: ${snapshot.stackTrace}'),
),
];
} else {
switch (snapshot.connectionState) {
case ConnectionState.none:
children = const <Widget>[
Icon(
Icons.info,
color: Colors.blue,
size: 60,
),
Padding(
padding: EdgeInsets.only(top: 16),
child: Text('Select a lot'),
)
];
break;
case ConnectionState.waiting:
children = const <Widget>[
SizedBox(
child: CircularProgressIndicator(),
width: 60,
height: 60,
),
Padding(
padding: EdgeInsets.only(top: 16),
child: Text('Awaiting bids...'),
)
];
break;
case ConnectionState.active:
children = <Widget>[
const Icon(
Icons.check_circle_outline,
color: Colors.green,
size: 60,
),
Padding(
padding: const EdgeInsets.only(top: 16),
child: Text('\$${snapshot.data}'),
)
];
break;
case ConnectionState.done:
children = <Widget>[
const Icon(
Icons.info,
color: Colors.blue,
size: 60,
),
Padding(
padding: const EdgeInsets.only(top: 16),
child: Text('\$${snapshot.data} (closed)'),
)
];
break;
}
}
return Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: children,
);
},
),
],
),
);