主体可能正常完成的错误，导致返回'null‘，但是返回类型'Widget’是一个潜在的不可空类型。
主体可能正常完成的错误，导致返回'null‘，但是返回类型'Widget’是一个潜在的不可空类型。
提问于 2022-04-19 13:33:11
Widget build(BuildContext context) {
return StreamBuilder<User>(
stream: widget.auth.authStateChanges(),
builder: (context, snapshot) {
// showing Error in this part(The body might complete normally, causing
// 'null' to be returned, but the return type, 'Widget',
// is a potentially non-nullable type. Also showing
// type '_AsBroadcastStream<User?>' is not a subtype of type 'Stream<User>?')
if (snapshot.connectionState == ConnectionState.active) {
User? user = snapshot.Data;
if (_user == null) {
return LoginScreen(
onSignIn: _updateUser,
auth: widget.auth,
);
}
return Home(
onSignOut: () => _updateUser(null!),
auth: widget.auth,
);
}
},
);
}在本部分中显示错误：
主体可能正常完成，导致返回'null‘，但是返回类型'Widget’是一个潜在的不可空类型.
。
回答 1
Stack Overflow用户
回答已采纳
发布于 2022-04-19 13:54:38
问题是在所有情况下，构建器都需要返回一个小部件。当if (snapshot.connectionState == ConnectionState.active)不是真的时，它就不会这么做。例如，你可以这样做
Widget build(BuildContext context) {
return StreamBuilder<User>(
stream: widget.auth.authStateChanges(),
builder: (context, snapshot) {
// showing Error in this part(The body might complete normally, causing
// 'null' to be returned, but the return type, 'Widget',
// is a potentially non-nullable type. Also showing
// type '_AsBroadcastStream<User?>' is not a subtype of type 'Stream<User>?')
if (snapshot.connectionState == ConnectionState.active) {
User? user = snapshot.Data;
if (_user == null) {
return LoginScreen(
onSignIn: _updateUser,
auth: widget.auth,
);
}
return Home(
onSignOut: () => _updateUser(null!),
auth: widget.auth,
);
}
return SizedBox(); //you need to return some widget here. this is an example
},
);
}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/71925864
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