Getting subfield data flutter firestore

i have a education collection with currentuser uid as document, inside there is some of subfield i created with form. then i want to display it with listview after get the data with get firestore function.

  Future _getDataEducation() async {
    await FirebaseFirestore.instance
        .collection("education")
        .doc(FirebaseAuth.instance.currentUser!.uid)
        .get()
        .then((snapshot) async {
      if (snapshot.exists) {
        if (mounted) {
          setState(() {
            SD = snapshot.data()!["SD"];
            SMP = snapshot.data()!["SMP"];
            SMA = snapshot.data()!["SMA"];
            College = snapshot.data()!["College"]; //how to write it correctly? with subfield
          });
        }
      }
    });
  }

this is how i display it but it gets null because i didn't get it correctly in _getDataEducation()

Container(
                          height: 400,
                          child: ListView(
                            children: [
                              SizedBox(
                                height: 20,
                              ),
                              Column(
                                children: [
                                  Text(
                                    SD == null
                                        ? Text("no data").toString()
                                        : SD!,
                                    style: const TextStyle(
                                        fontWeight: FontWeight.bold,
                                        fontSize: 24),
                                 开发者_运维技巧 ),
                                  const SizedBox(
                                    height: 5,
                                  ),
                                  Text(
                                    SMP == null
                                        ? Text("no data").toString()
                                        : SMP!,
                                    style: const TextStyle(
                                        color: Colors.grey, fontSize: 16),
                                  ),
                                  const SizedBox(
                                    height: 5,
                                  ),
                                  Text(
                                    SMA == null
                                        ? Text("no data").toString()
                                        : SMA!,
                                    style: const TextStyle(
                                        color: Colors.grey, fontSize: 16),
                                  ),
                                  Text(
                                    College == null
                                        ? Text("no data").toString()
                                        : College!,
                                    style: const TextStyle(
                                        color: Colors.grey, fontSize: 16),
                                  ),
                                ],
                              ),
                            ],
                          ),
                        ),

how to display subfield firestore in flutter?