在构建StreamBuilder<DocumentSnapshot>时抛出了NoSuchMethodError
在构建StreamBuilder<DocumentSnapshot>时抛出了NoSuchMethodError
提问于 2021-01-14 18:41:14
实际上，我正在遵循基于角色的身份验证的教程。问题是，当我第一次登录时，我会像预期的那样导航到右侧屏幕，而快照确实有数据！User: {role: admin, last_login: Timestamp(seconds=1610430754, nanoseconds=74000000), name: bilal, created_at: Timestamp(seconds=1610429038, nanoseconds=204000000), build_number: 1, email: bilalsaeed781833@gmail.com}
但当我在移动的屏幕上创建另一个用户时，同一个Stream builder再次检查基于角色的身份验证，快照没有数据。
User: null UserDoc: Instance of 'DocumentSnapshot'
======== Exception caught by widgets library =======================================================
The following NoSuchMethodError was thrown building StreamBuilder<DocumentSnapshot>(dirty, state: _StreamBuilderBaseState<DocumentSnapshot, AsyncSnapshot<DocumentSnapshot>>#0f4cc):
The method '[]' was called on null.
Receiver: null
Tried calling: []("role")我不知道为什么它会给出这个错误！
下面是我的代码：
return StreamBuilder<User>(
stream: FirebaseAuth.instance.authStateChanges(),
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.active) {
return StreamBuilder<DocumentSnapshot>(
stream: FirebaseFirestore.instance
.collection("users")
.doc(snapshot.data.uid)
.snapshots(),
builder: (BuildContext context,
AsyncSnapshot<DocumentSnapshot> snapshot) {
if (snapshot.connectionState == ConnectionState.active) {
final userDoc = snapshot.data;
final user = userDoc.data();
debugPrint("User: ${user.toString()} UserDoc: ${userDoc.toString()} ");
if (user['role'] == 'admin') {
return admin();
} else if (user['role'] == 'hod') {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => hod()),
);
} else if (user['role'] == 'duo') {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => duo()),
);
} else if (user['role'] == 'teacher') {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => teacher()),
);
} else if (user['role'] == 'cr') {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => cr()),
);
} else if (user['role'] == 'student') {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => student()),
);
} else {
return Material(
child: Center(
child: CircularProgressIndicator(),
),
);
}
}
return Material(
child: Center(
child: CircularProgressIndicator(),
),
);
},
);
}
return Material(
child: Center(
child: CircularProgressIndicator(),
),
);
});回答 1
Stack Overflow用户
发布于 2021-01-14 19:42:05
将StreamBuilder中的所有内容都包装在一个if语句中。
if (snapshot.connectionState == ConnectionState.active) {
if(snapshot.hasData){
...
} else {
return CircularProgressIndicator()
}
}这应该可以防止构建器在没有数据的情况下尝试构建某些东西。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/65717456
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