如何在 Dart 中过滤列表

Question

I'm getting my DocumentSnapshots from Firebase and I'm trying to delete the document where the user ID match but the userList is always returning the 4 records.

List<DocumentSnapshot> userList = new List<DocumentSnapshot>();

                        userList = snapshot.data.documents.map((DocumentSnapshot docSnapshot) {
                          //print("ACTUAL USER :: " + docSnapshot.data['userId']);
                          if (docSnapshot.data['userId'] != id) {
                            return docSnapshot;
                          } else {
                            print('FOUND IT: ' + id);
                            userList.remove(docSnapshot.data);
                            //userList.removeWhere((docSnapshot) => 'userId' == id);
                          }
                        }).toList();

print('userList Size: ' + userList.length.toString());

The validation works ("Found it") but none of my tests where able to delete the user from document list.

Can someone advise please?

Answer 1

You are trying to remove the element from your List before it was even added.
Specifically, the map function will assign a List to your userList variable after it has mapped the snapshots.
From your code I can tell that you do not actually want to perform any mapping but only filtering .

In Dart, you can filter using the Iterable.where .
In your case that would look something like this:

final List<DocumentSnapshot> userList = snapshot.data.documents
      .where((DocumentSnapshot documentSnapshot) => documentSnapshot['userId'] != id).toList();

I am assuming that you only want documents that do not have a userId of id , otherwise, you would have to use an == operator instead.

You could also useList.removeWhere by assigning all the documents to your userList first and then calling removeWhere :

final List<DocumentSnapshot> userList = snapshot.data.documents;

userList.removeWhere((DocumentSnapshot documentSnapshot) => documentSnapshot['userId'] != id).toList();