Flutter - Firebase RTDB，在 null 上调用了 forEach 方法

Question

The only this I changed in my code and Firebase rtdb is where the data is being fetched from.

Before data was in: "users" - "parents" (Code worked perfectly here)

Now data is in: "users" - schoolName.toString() - "parents" (Code causes an error)

How can I approach/solve this issue?

Thanks.

Error:

E/flutter ( 8683): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: NoSuchMethodError: The method 'forEach' was called on null.

E/flutter ( 8683): Tried calling: forEach(Closure: (dynamic, dynamic) => void)

Code:

Future<List> getParentDetails() async {
    schoolName = await getSchoolName();
    databaseReference
        .child("users")
        .child(schoolName.toString())
        .child("parents")
        .onValue
        .listen(
      (event) {
        if (event.snapshot.exists) {
          setState(
            () {
              var value = event.snapshot.value;
              parentList = Map.from(value)
                  .values
                  .map((e) => Parents.fromJson(Map.from(e)))
                  .toList();
            },
          );
        } else {
          print("No Data Exists");
        }
      },
    );
    return parentList;
  }

UI Code:

ListView.builder(
              itemCount: parentList.length,
              itemBuilder: (context, int index) {
                final Parents parents = parentList[index];
                final String driverEmail = parents.email;
                final String driverName = parents.name;
                final String driverPhone = parents.phone;
                // final driverRandomId = parents.randomId;
                // final String driverUID = driver.uid;
                return Padding(
                  padding: const EdgeInsets.all(8.0),
                  child: Card(
                    elevation: 0.2,
                    child: ExpansionTile(
                      // collapsedBackgroundColor: Colors.grey,
                      title: Text(
                        driverName.toUpperCase(),
                        style: GoogleFonts.lexendMega(
                          fontSize: 12,
                        ),
                        textAlign: TextAlign.center,
                      ),
                      children: [
                        Column(
                          children: [
                            Text(
                              driverEmail,
                              textAlign: TextAlign.center,
                              style: GoogleFonts.lexendMega(fontSize: 12),
                            ),
                            SizedBox(
                              height: 5,
                            ),
                            Text(
                              driverPhone,
                              textAlign: TextAlign.center,
                              style: GoogleFonts.lexendMega(fontSize: 12),
                            ),
                            SizedBox(
                              height: 5,
                            ),
                          ],
                        )
                      ],
                    ),
                  ),
                );
              },
            ),

Class Code:

class Parents {
  final String email;
  final String name;
  final String phone;

  Parents({
    this.email,
    this.name,
    this.phone,
  });

  static Parents fromJson(Map<String, String> json) {
    return Parents(
      email: json['email'],
      name: json['name'],
      phone: json['phone'],
    );
  }
}

Answer 1

You should be able to check whether your snapshot has some data (I'm assuming it returns an AsyncSnapshot , which is also used by widgets like StreamBuilder and FutureBuilder .

https://api.flutter.dev/flutter/widgets/AsyncSnapshot-class.html

In that case, you can call event.snapshot.hasData to determine whether data is null. If it is, you can instead return an empty list.

I assume you're using this approach as opposed to a FutureBuilder to keep your business logic and UI separate? If there's no specific reasoning, you might want to consider to instead use a FutureBuilder or StreamBuilder instead.