如何使用 flutter 在 Firestore 中特定文档的字段内检索 Map 值？

Question

I want to get all the Values of the map which is under "Subjects" field. And I also want to listen if any updates or changes made to those values. I actually want to add al those values and store in a variable. Can someone please tell me how can i achieve this?

Here is the structure of the collection.

This is how im adding the subjects whenever a user enters the subject name

onPressed: () async {
                      temp = qrdataFeed.text;
                        int index = qrdataFeed.text.indexOf('-');
                        subject = qrdataFeed.text.substring(0, index);
                        print("Subject name is $subject");
                        numberOfClasses = await FirebaseFirestore.instance
                            .collection('tutors')
                            .doc(uid)
                            .get()
                            .then((doc) async {
                          Map<String, dynamic> map = await doc.data();
                          if (!map.containsKey('Subjects')) {
                            await tutor_details.doc(uid).set({
                              'Subjects': {'$subject': initialValue},
                            }, SetOptions(merge: true));
                          }
                          if (doc.data()['Subjects']['$subject'] !=
                              '$subject') {
                            if (!map.containsKey('$subject')) {
                              await tutor_details.doc(uid).set({
                                'Subjects': {'$subject': initialValue}
                              }, SetOptions(merge: true));
                            }
                          }
                          var val = await doc.data()['Subjects']['$subject'];
                          return val;
                        });

                        if (!mounted) return;
                        setState(() {
                          qrData = qrdataFeed.text;
                          scanned = true;
                          print('done');
                          //if (temp != qrdataFeed.text)
                          numberOfClasses += 1;
                          print('$numberOfClasses is printed');
                        });
                        await tutor_details.doc(uid).set({
                          'Subjects': {'$subject': numberOfClasses},
                        }, SetOptions(merge: true));
                      }
                    },

Answer 1

Posting the @NisanthReddy's solution as a Community Wiki for visibility.

A better architecture would be to have one class at the root to handle all your transactions and to also notify any listener in your code.

You should always call this class to update and you can add listeners to this class from any widget you want. This way you will have everything Firestore-related in one place.