Issue
After migrating to null safety I’m getting an error on ListView as "The argument type ‘Object?’ can’t be assigned to the parameter type ‘List’."
I’m getting error on return ListView(children: snapshot.data,);
Can anyone help me to fix this error and build a ListView for activityfeeditem in my app?
Here is my code for activity_feed.dart,
class ActivityFeed extends StatefulWidget {
@override
_ActivityFeedState createState() => _ActivityFeedState();
}
class _ActivityFeedState extends State<ActivityFeed> {
getActivityFeed() async {
QuerySnapshot snapshot = await activityFeedRef
.doc(currentUser!.id)
.collection('feedItems')
.orderBy('timestamp', descending: true)
.limit(50)
.get();
List<ActivityFeedItem> feedItems = [];
snapshot.docs.forEach((doc) {
feedItems.add(ActivityFeedItem.fromDocument(doc));
print('Activity Feed Item: ${doc.data}');
});
return feedItems;
}
@override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.deepPurple[50],
appBar: header(context, titleText: "Activity Feed"),
body: Container(
child: FutureBuilder(
future: getActivityFeed(),
builder: (context, snapshot) {
if (!snapshot.hasData) {
return circularProgress();
}
return ListView(
children: snapshot.data,
// Here I'm getting error on `snapshot.data`
);
},
),
),
);
}
}
Widget? mediaPreview;
String? activityItemText;
class ActivityFeedItem extends StatelessWidget {
final String? username;
final String? userId;
final String? type; // 'like', 'follow', 'comment'
final String? mediaUrl;
final String? postId;
final String? userProfileImg;
final String? commentData;
final Timestamp? timestamp;
ActivityFeedItem({
this.username,
this.userId,
this.type,
this.mediaUrl,
this.postId,
this.userProfileImg,
this.commentData,
this.timestamp,
});
factory ActivityFeedItem.fromDocument(DocumentSnapshot doc) {
return ActivityFeedItem(
username: doc['username'],
userId: doc['userId'],
type: doc['type'],
postId: doc['postId'],
userProfileImg: doc['userProfileImg'],
commentData: doc['commentData'],
timestamp: doc['timestamp'],
mediaUrl: doc['mediaUrl'],
);
}
showPost(context) {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => PostScreen(postId: postId, userId: userId)));
}
configureMediaPreview(context) {
if (type == "like" || type == 'comment') {
mediaPreview = GestureDetector(
onTap: () => showPost(context),
child: Container(
height: 50.0,
width: 50.0,
child: AspectRatio(
aspectRatio: 16 / 9,
child: Container(
decoration: BoxDecoration(
image: DecorationImage(
fit: BoxFit.cover,
image: CachedNetworkImageProvider(mediaUrl!),
),
),
)),
),
);
} else {
mediaPreview = Text('');
}
if (type == 'like') {
activityItemText = "liked your post";
} else if (type == 'follow') {
activityItemText = "is following you";
} else if (type == 'comment') {
activityItemText = 'replied: $commentData';
} else {
activityItemText = "Error: Unknown type '$type'";
}
}
@override
Widget build(BuildContext context) {
configureMediaPreview(context);
return Padding(
padding: EdgeInsets.only(bottom: 2.0),
child: Container(
color: Colors.white54,
child: ListTile(
title: GestureDetector(
onTap: () => showProfile(context, profileId: userId),
child: RichText(
overflow: TextOverflow.ellipsis,
text: TextSpan(
style: TextStyle(
fontSize: 14.0,
color: Colors.black,
),
children: [
TextSpan(
text: username,
style: TextStyle(fontWeight: FontWeight.bold),
),
TextSpan(
text: ' $activityItemText',
),
]),
),
),
leading: CircleAvatar(
backgroundImage: CachedNetworkImageProvider(userProfileImg!),
),
subtitle: Text(
timeago.format(timestamp!.toDate()),
overflow: TextOverflow.ellipsis,
),
trailing: mediaPreview,
),
),
);
}
}
showProfile(BuildContext context, {String? profileId}) {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => Profile(
profileId: profileId,
),
),
);
}
I have tried many ways but I counldn’t figure out how I can fix this
New code for list
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.deepPurple[50],
appBar: header(context, titleText: "Activity Feed"),
body: Container(
child: StreamBuilder<QuerySnapshot>(
stream: activityFeedRef
.doc(currentUser!.id)
.collection('feedItems')
.orderBy('timestamp', descending: true)
.limit(50)
.snapshots(),
builder: (context, snapshot) {
if (!snapshot.hasData) {
return Center(
child: circularProgress(),
);
} else
return ListView(
children: snapshot.data!.docs.map((doc) {
return Card(
child: ListTile(
title: GestureDetector(
onTap: () =>
showProfile(context, profileId: doc['userId']),
child: RichText(
overflow: TextOverflow.ellipsis,
text: TextSpan(
style: TextStyle(
fontSize: 14.0,
color: Colors.black,
),
children: [
TextSpan(
text: doc['username'],
style: TextStyle(
fontWeight: FontWeight.bold),
),
TextSpan(
text: ' $activityItemText',
),
]),
),
),
leading: CircleAvatar(
backgroundImage: CachedNetworkImageProvider(
doc['userProfileImg']!),
),
subtitle: Text(
timeago.format(doc['timestamp']!.toDate()),
overflow: TextOverflow.ellipsis,
),
trailing: mediaPreview,
),
);
}).toList(),
);
}),
));
}
Solution
Chage your getActivityFeed
Future<List<ActivityFeedItem>> getActivityFeed() async {
try{
QuerySnapshot snapshot = await activityFeedRef
.doc(currentUser!.id)
.collection('feedItems')
.orderBy('timestamp', descending: true)
.limit(50)
.get();
List<ActivityFeedItem> feedItems = [];
snapshot.docs.forEach((doc) {
feedItems.add(ActivityFeedItem.fromDocument(doc));
print('Activity Feed Item: ${doc.data}');
});
return feedItems;
}
catch (error) {
print(error);
return <ActivityFeedItem>[];
}}
change you FutureBuilder as follows
FutureBuilder<List<ActivityFeedItem>>(
future: getActivityFeed(),
builder: (BuildContextcontext, AsyncSnapshot<List<ActivityFeedItem>> snapshot) {
if (snapshot.hasError){
return Center(child: Text("You have an error in loading
data"));
}
if (snapshot.hasData) {
return ListView(
children: snapshot.data!,
);
}
return CirclularProgressIndicator();
Answered By – Lakmal Fernando
Answer Checked By – Robin (FlutterFixes Admin)