如何解决退出后显示“用于空值的空检查运算符”
在我的应用上从 firebase 注销后，我收到以下消息。
*空检查运算符用于空值
抛出异常时，这是堆栈：
#0 MainScreenPage.build..
（包：Flutter_book_tracker_app/screens/main_screen_page.dart:274:49）
用于空值的空检查运算符
抛出异常时，这是堆栈：
#0 MainScreenPage.build.. (package:Flutter_book_tracker_app/screens/main_screen_page.dart:66:45)
RenderFlex 在底部溢出了 199462 像素。
相关的导致错误的小部件是：
列文件:///Users/junko/AndroidStudioProjects/Flutter_book_tracker_app/Flutter_book_tracker_app/lib/screens/main_screen_page.dart:132:13
右侧的 RenderFlex 溢出了 99671 像素。 相关的导致错误的小部件是： AppBar file:///Users/junko/AndroidStudioProjects/Flutter_book_tracker_app/Flutter_book_tracker_app/lib/screens/main_screen_page.dart:36:15*
- 显示的所有错误都在 main_screen_page.dart 上，但退出后模拟器窗口显示 login_screen_page。
- 单击模拟器上的 [后退] 按钮时，模拟器显示 main_screen_page.dart 和“用于空值的空检查运算符”和“底部的 RenderFlex 溢出 199462 像素”错误。
class MainScreenPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
CollectionReference userCollectionReference =
FirebaseFirestore.instance.collection('users');
CollectionReference bookCollectionReference =
FirebaseFirestore.instance.collection('books');
List<Book> userBooksReadList = [];
// int booksRead = 0;
var authUser = Provider.of<User?>(context);
return Scaffold(
appBar: AppBar(
backgroundColor: Colors.white24,elevation: 0,toolbarHeight: 77,centerTitle: false,title: Row(
children: [
Image.asset(
'assets/images/Icon-76.png',scale: 2,),Text(
'A.Reader',style: Theme.of(context).textTheme.headline6!.copyWith(
color: Colors.redAccent,fontWeight: FontWeight.bold),],actions: [
StreamBuilder<QuerySnapshot>(
stream: userCollectionReference.snapshots(),builder: (context,snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return Center(
child: CircularProgressIndicator(),);
}
final userListStream = snapshot.data!.docs.map((user) {
return MUser.fromDocument(user);
}).where((user) {
return (user.uid == authUser!.uid);
}).toList();
MUser curUser = userListStream[0];
return Column(
children: [
SizedBox(
height: 40,width: 40,child: InkWell(
onTap: () {
showDialog(
context: context,builder: (context) {
return createProfileDialog(
context,curUser,userBooksReadList);
},);
},child: CircleAvatar(
radius: 60,backgroundImage: NetworkImage(curUser.avatarUrl ??
'https://picsum.photos/id/1022/300'),backgroundColor: Colors.white,child: Text(''),Text(
curUser.displayName.toupperCase(),overflow: TextOverflow.ellipsis,style: TextStyle(color: Colors.black),)
],);
},TextButton.icon(
onpressed: () {
FirebaseAuth.instance.signOut().then((value) {
return Navigator.push(
context,MaterialPageRoute(
builder: (context) => LoginPage(),));
});
},icon: Icon(Icons.logout),label: Text(''),floatingActionButton: FloatingActionButton(
onpressed: () {
Navigator.push(
context,MaterialPageRoute(
builder: (context) => BookSearchPage(),));
},child: Icon(
Icons.add,backgroundColor: Colors.redAccent,body: Column(
children: [
Container(
width: double.infinity,margin: const EdgeInsets.only(top: 12,left: 12,bottom: 10),child: RichText(
text: TextSpan(
style: Theme.of(context).textTheme.headline6,children: [
TextSpan(text: '今、'),TextSpan(
text: '読んでいるのは',style: TextStyle(fontWeight: FontWeight.w600)),TextSpan(text: '…'),]),SizedBox(
height: 10,StreamBuilder<QuerySnapshot>(
stream: bookCollectionReference.snapshots(),snapshot) {
if (snapshot.hasError) {
return Text('問題が発生しました (T.T)');
}
if (snapshot.connectionState == ConnectionState.waiting) {
return Expanded(
flex: 1,child: Center(
child: CircularProgressIndicator(
strokeWidth: 2,color: Colors.lime.shade300,)));
}
if (snapshot.data!.docs.isEmpty) {
return Text('表示する書籍データがありません',style: Theme.of(context).textTheme.headline4);
}
final userBookFilteredReadListStream =
snapshot.data!.docs.map((book) {
return Book.fromDocument(book);
}).where((book) {
return ((book.userId == authUser!.uid)) &&
(book.finishedReading == null) &&
(book.startedReading != null);
}).toList();
userBooksReadList = snapshot.data!.docs.map((book) {
return Book.fromDocument(book);
}).where((book) {
return ((book.userId == authUser!.uid)) &&
(book.finishedReading != null) &&
(book.startedReading != null);
}).toList();
return Expanded(
flex: 1,child: (userBookFilteredReadListStream.length > 0)
? ListView.builder(
scrollDirection: Axis.horizontal,itemCount: userBookFilteredReadListStream.length,itemBuilder: (context,index) {
Book book = userBookFilteredReadListStream[index];
return InkWell(
child: ReadingListCard(
buttonText: '読書中',image: book.photoUrl!,title: book.title,author: book.author!,rating: book.rating!,onTap: () {
showDialog(
context: context,builder: (context) {
return BookDetailDialog(
book: book,);
},);
},);
},)
: Text('読書中の本はありません (・o・)',style: Theme.of(context).textTheme.headline6));
},Container(
width: double.infinity,margin: EdgeInsets.only(left: 10),child: Column(
crossAxisAlignment: CrossAxisAlignment.start,children: [
RichText(
text: TextSpan(children: [
TextSpan(
text: '読みたい本リスト',style: TextStyle(
fontSize: 24,fontWeight: FontWeight.w600,color: kBlackColor),SizedBox(
height: 8,)));
}
if (snapshot.data!.docs.isEmpty) {
return Center(
child: Text('表示する書籍データがありません',style: Theme.of(context).textTheme.headline4),);
}
final readingListListBook = snapshot.data!.docs.map((book) {
return Book.fromDocument(book);
// ログイン中ユーザのuidでbookをフィルタリングする
}).where((book) {
return ((book.userId == authUser!.uid)) &&
(book.startedReading == null) &&
(book.finishedReading == null);
}).toList();
return Expanded(
flex: 1,child: (readingListListBook.length > 0)
? ListView.builder(
scrollDirection: Axis.horizontal,itemCount: readingListListBook.length,index) {
Book book = readingListListBook[index];
return InkWell(
child: ReadingListCard(
buttonText: '未読',isBookRead: false,)
: Text('表示する書籍データがありません ^_^;',);
}
}
“认证用户！” 退出后似乎导致了空检查问题，因为退出时authUser变为空。
我尝试通过在每次出现 authUser! 之前添加“if (authUser == null) {}”来解决空检查问题，但最终出现错误“setState() 或 markNeedsBuild() 在构建期间调用”和“' package:Flutter/src/widgets/navigator.dart': 失败的断言: line 4564 pos 12: '!_debugLocked': is not true。" （在同样的两个 RenderFlex 问题之上。）
有人能帮我解决这些问题吗？非常感谢您的帮助。
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