Was unable to sort a list of objects in flutter

Question

I was working on a project where I need to sort a list that has objects in it, but it's giving an error.

The expression here has a type of 'void', and therefore can't be used.

Here my code:-

    @override
  void initState() {
    super.initState();
    subscription = collectionReference.snapshots().listen((datasnapshot) {
      setState(() {
        messageList = datasnapshot.documents
            .map(
              (v) => Message(
                  message: v.data['msg'],
                  sender: v.data['sender'],
                  imgUrl: v.data['imgUrl'],
                  id: v.data['id']),
            )
            .toList().sort((m, m2) => int.parse(m.id).compareTo(int.parse(m2.id)));


      });
    });
  }

Its raising error at sort method :-

.toList().sort((m, m2) => int.parse(m.id).compareTo(int.parse(m2.id)));

What should I do to fix it, or is there any other way to sort a list of objects.

One more extra question. Documents in my firestore collection are not being added chronologically-sorted. so, I have to do that manually. do anyone knows why they are not being chronologically-sorted as default?

Thanks in advance.

Solution

sort method doesn't return a list, it is a void function. You should do it like this:

messageList = datasnapshot.documents
        .map(
          (v) => Message(
              message: v.data['msg'],
              sender: v.data['sender'],
              imgUrl: v.data['imgUrl'],
              id: v.data['id']),
        )
        .toList()

messageList.sort((m, m2) => int.parse(m.id).compareTo(int.parse(m2.id)));

Comments

[Hardeep Singh]

Thanks for editing. I am not that good at English. I will improve it. Thanks

[PYB]

Documents are not added chronologically-sorted because this is done at the query level. Indexing is already applied automatically when new documents are added, which is how the query can sort the documents quickly.

[Hardeep Singh]

yeah, that totally makes sense. Thanks for your answer. I was struggling for it from couple of hours. Really appreciated. Thanks ones again.

[Dpedrinha]

I can't find the difference between this answer and the code in the question. Did you edit it to match this answer?