我一直在尝试运行一个flutter应用程序，但它一直给我失败的断言错误。下面是我的代码。我只想向列表显示第二个代码
class Post extends StatefulWidget {
final String postId;
final String ownerId;
final String username;
final String location;
final String description;
final String mediaUrl;
final dynamic likes;
Post({
this.postId,
this.ownerId,
this.username,
this.location,
this.description,
this.mediaUrl,
this.likes,
});
factory Post.fromDocument(DocumentSnapshot doc) {
return Post(
postId: doc['postId'],
ownerId: doc['ownerId'],
username: doc['username'],
location: doc['location'],
description: doc['description'],
mediaUrl: doc['mediaUrl'],
likes: doc['likes'],
);
}
int getLikeCount(likes) {
// if no likes, return 0
if (likes == null) {
return 0;
}
int count = 0;
// if the key is explicitly set to true, add a like
likes.values.forEach((val) {
if (val == true) {
count += 1;
}
});
return count;
}
@override
_PostState createState() => _PostState(
postId: this.postId,
ownerId: this.ownerId,
username: this.username,
location: this.location,
description: this.description,
mediaUrl: this.mediaUrl,
likes: this.likes,
likeCount: getLikeCount(this.likes),
);
}
class _PostState extends State<Post> {
final String postId;
final String ownerId;
final String username;
final String location;
final String description;
final String mediaUrl;
Int likeCount;
Map likes;
_PostState({
this.postId,
this.ownerId,
this.username,
this.location,
this.description,
this.mediaUrl,
this.likes,
this.likeCount,
});
Widget postingHeading() {
return FutureBuilder(
future:
FirebaseFirestore.instance.collection('User').doc(ownerId).get(),
builder: (context, snapshot) {
if (!snapshot.hasData) {
return CircularProgressIndicator();
}
return ListTile(
onTap: () => print('go check the url'),
leading: CircleAvatar(
backgroundImage:
NetworkImage("${snapshot.data.data()['photoUrl']}"),
),
title: Text('${snapshot.data.data()['username']}'),
subtitle: Text(location),
trailing: IconButton(
onPressed: () => print('deleting post'),
icon: Icon(Icons.more_vert),
),
);
});
}
Widget postImagePicture() {
return Stack(
alignment: Alignment.center,
children: [
Image.network(mediaUrl),
],
);
}
Widget postDetailsComment() {
return Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Row(
children: [
IconButton(icon: Icon(Icons.favorite_border), onPressed: () {}),
IconButton(icon: Icon(Icons.favorite_border), onPressed: () {})
],
),
Row(
children: <Widget>[
Container(
margin: EdgeInsets.only(left: 20.0),
child: Text(
"$likeCount likes",
style: TextStyle(
color: Colors.black,
fontWeight: FontWeight.bold,
),
),
),
],
),
Row(
children: [
Text(username),
SizedBox(
width: 1,
),
Flexible(child: Text(description))
],
)
],
);
}
@override
Widget build(BuildContext context) {
return Column(
mainAxisSize: MainAxisSize.min,
children: [
postingHeading(),
postImagePicture(),
postDetailsComment(),
],
);
}
}
这是我将其转换为列表的地方。。。我甚至不知道哪里出了问题。。。。请帮忙。。。。提前感谢
class Profile extends StatefulWidget {
final String currentUser;
Profile({this.currentUser});
@override
_ProfileState createState() => _ProfileState();
}
class _ProfileState extends State<Profile> {
final _firestore = FirebaseFirestore.instance;
int postLenght;
List<Post> post;
bool pleaseWait;
@override
void initState() {
super.initState();
getUsersPicsDetails();
}
getUsersPicsDetails() async {
setState(() {
pleaseWait = false;
});
QuerySnapshot _getPost = await _firestore
.collection('post')
.doc(widget.currentUser)
.collection('userPost')
.orderBy('timeStamp', descending: true)
.get();
setState(() {
pleaseWait = true;
postLenght = _getPost.docs.length;
post = _getPost.docs.map((e) => Post.fromDocument(e)).toList();
print(postLenght);
});
}
fellowEditButtton({String test, Function press}) {
return TextButton(
onPressed: press,
child: Container(
alignment: Alignment.center,
height: 25,
width: 250,
decoration: BoxDecoration(
color: Theme.of(context).primaryColor,
border: Border.all(),
borderRadius: BorderRadius.circular(8.0)),
child: Text(
test,
style: TextStyle(color: Colors.white, fontWeight: FontWeight.bold),
)),
);
}
gettingUserprofile() {
return StreamBuilder(
stream: _firestore.collection('User').doc(widget.currentUser).snapshots(),
builder:
(BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
if (!snapshot.hasData) {
return Center(child: CircularProgressIndicator());
}
if (snapshot.connectionState != ConnectionState.active) {
return Text('this stuff en');
}
return ListView.builder(
itemCount: 1,
itemBuilder: (context, index) => Container(
padding: EdgeInsets.all(8.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Row(
children: [
FullScreenWidget(
child: Hero(
tag: 'smallImage',
child: CircleAvatar(
backgroundImage: NetworkImage(
'${snapshot.data.data()['photoUrl']}'),
radius: 50.0,
),
),
),
Expanded(
flex: 1,
child: Column(
children: [
Row(
mainAxisAlignment:
MainAxisAlignment.spaceEvenly,
children: [
topColum(buttom: 'Post', number: 1),
topColum(buttom: 'Fellowers', number: 2),
topColum(buttom: 'Following', number: 0),
],
),
Column(
crossAxisAlignment:
CrossAxisAlignment.stretch,
children: [
Padding(
padding: const EdgeInsets.symmetric(
horizontal: 20.0,
),
child: widget.currentUser ==
_auth.currentUser.uid
? fellowEditButtton(
test: 'Edit Profile',
press: profileEditingButton)
: fellowEditButtton(
test: 'Fellow', press: () {})),
],
),
],
),
),
],
),
Divider(),
//! this is i call the list
//getUserPicture(),
getUserPicture(),
],
),
));
},
);
}
profileEditingButton() {
Navigator.push(
context,
MaterialPageRoute(
builder: (_) => EditProfile(
userProfile: widget.currentUser,
)));
}
Widget topColum({int number, String buttom}) {
return Column(
children: [
Text(
'$number',
style: TextStyle(
fontWeight: FontWeight.bold,
fontSize: 20,
),
),
Text(
buttom,
style: TextStyle(
fontSize: 20,
),
),
],
);
}
//! this is the where i return the list
Widget getUserPicture() {
if (pleaseWait = false) {
return CircularProgressIndicator();
}
return Column(
children: post,
);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: header(context, titleString: "Profile"),
body:
//Text('${widget.currentUser}')
gettingUserprofile());
// userPictursPost(),
}
}
我想得到底部的帖子。。。提前感谢下面是错误图像
在此处输入图像描述
当您收到错误时，请将其与您的问题一起发布。当你遇到错误时，这意味着你的代码有问题，很可能不是flutter引擎。两者对于调试都很重要，错误+代码。
尝试更改此
QuerySnapshot _getPost = await _firestore
.collection('post')
.doc(widget.currentUser)
.collection('userPost')
.orderBy('timeStamp', descending: true)
.get();
setState(() {
pleaseWait = true;
postLenght = _getPost.docs.length;
post = _getPost.docs.map((e) => Post.fromDocument(e)).toList();
print(postLenght);
});
进入这个：
QuerySnapshot _getPost = await _firestore
.collection('post')
.doc(widget.currentUser)
.collection('userPost')
.orderBy('timeStamp', descending: true)
.get();
if(_getPost.docs.isNotEmpty){
List<Post> tempPost = _getPost.docs.map((e) => Post.fromDocument(e)).toList();
setState(() {
pleaseWait = true;
post =tempPost
print(postLenght);
});
}else{
print('The List is empty);}
您没有检查查询结果是否有数据。如果它是空的，你会在树下传递一个空的List帖子，你会得到你所遇到的错误。
对于面临类似问题的人，让我告诉他们我在代码中发现了什么：
错误表明子项为null，而不是空的
因此，如果您从一个单独的方法获取父小部件(如Row或Column(的子部件，只需检查您是否从方法返回构造的子小部件。
Row(
children: getMyRowChildren()
)
.
.
.
getMyRowChildren(){
Widget childWidget = ... //constructed
return childWidget; //don't forget to return!
}
否则它将返回null，这将导致子级为null，我们会得到上面提到的错误！