我想在构建小工具之前从两个流中获得数据。第一个流为数据库路径提供uid。我不能压缩这两个流,因为我需要首先获得uid来构建第二个数据。
我尝试使用嵌套流,但总是出错
在null上调用了方法'[]‘。接收者:尝试的呼叫为空:
给出了我的代码。我该如何解决这个问题呢?
class _DiabeticaState extends State<Diabetica> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
elevation: 0,
title: Text(
"Diabetica",
style: TextStyle(
color: Colors.black, fontWeight: FontWeight.w400, fontSize: 22),
),
centerTitle: true,
actions: <Widget>[
IconButton(
icon: Icon(Icons.monetization_on),
onPressed: () {},
),
],
),
body: StreamBuilder(
stream: FirebaseAuth.instance.onAuthStateChanged,
builder: (BuildContext context, user) {
if (user.hasData) {
String name = "";
String photoUri = "";
String u = "";
if (user.connectionState == ConnectionState.active) {
name = user.data.displayName;
photoUri = user.data.photoUrl;
u = user.data.uid;
return StreamBuilder(
stream: Firestore.instance.document('users/$u').snapshots(),
builder: (BuildContext context, db) {
if (db.hasData) {
double age = 0;
double height = 0;
double weight = 0;
double a1c = 0;
double bmr = 0;
if (db.connectionState == ConnectionState.active) {
age = db.data['age'];
height = db.data['height'];
weight = db.data['weight'];
a1c = db.data['a1c'];
bmr = db.data['bmr'];
return Container();
}
return Container(
);
}
return new LoadingScreen();
},
);
}
return new LoadingScreen();
}
return new LoginAlter();
},
),
);
}
}
发布于 2019-05-15 04:06:24
在您的例子中,由于您的实现,使用这个CombineLatestStream.combine2
不是正确的方式。您是否尝试过在第二个StreamBuilder上设置initialData
属性?
有关示例,请尝试查看此处:StreamBuilder initialData
https://stackoverflow.com/questions/56137214
复制相似问题