I have 3 issues from migrating to null-safety

Question

I migrated to null-safety today and I have 3 issues that I don't know how to fix. Below, I have provided the errors and the code that each error refers to. I do not know how to fix these issues and they are the only errors left.

error • The body might complete normally, causing 'null' to be returned, but the return type is a potentially non-nullable type at lib\Services\firestore_service.dart:29:16 • (body_might_complete_normally)

Future<Void> saveNewAgency(Agency agency) async {
    await _db.collection('agency').doc(globals.agencyId).set(agency.toMap());
  }

      error • The property 'docs' can't be unconditionally accessed because the receiver can be 'null' at lib\screens\agent_dash_board.dart:57:43 •(unchecked_use_of_nullable_value)
I fixed similar errors to this one with the code at itemCount: (snapshot.data! as QuerySnapshot).docs.length,  in the code snippet. 
    
    return new ListView.builder(
                          itemCount: (snapshot.data! as QuerySnapshot).docs.length,
                          itemBuilder: (BuildContext context, int index) {
                            Trxns trxns = Trxns.fromFirestore(
                                snapshot.data.docs[index].data());

  error • The body might complete normally, causing 'null' to be returned, but the return type is a potentially non-nullable type at lib\screens\appointment_calendar.dart:434:31 • (body_might_complete_normally)

Map<DateTime, List<Event?>> convertToMap(List<Event> item) {
    Map<DateTime, List>? result;

    for (int i = 0; i < item.length; i++) {
      Event data = item[i];
      //get the date and convert it to a DateTime variable
      //DateTime currentDate = DateFormat('MM-dd-yyyy - kk:mm').format(data.eventDate);
      DateTime currentDate = DateTime(data.eventDate!.year, data.eventDate!.month, data.eventDate!.day, data.eventDate!.hour, data.eventDate!.minute);

      List eventNames = [];
      //add the event name to the the eventNames list for the current date.
      //search for another event with the same date and populate the eventNames List.
      for (int j = 0; j < item.length; j++) {
        //create temp calendarItemData object.
        Event temp = item[j];
        //establish that the temp date is equal to the current date
        if (data.eventDate == temp.eventDate) {
          //add the event name to the event List.
          eventNames.add(temp.eventName);
        } //else continue
      }

      //add the date and the event to the map if the date is not contained in the map
      if (result == null) {
        result = {
          currentDate: eventNames
        };
      } else {
        result[currentDate] = eventNames;
      }
      return result as Map<DateTime, List<Event?>>;
    }
  }

mmcdon20 · Accepted Answer · 2021-06-25T18:43:24.047

Future<Void> saveNewAgency(Agency agency) async {
  await _db.collection('agency').doc(globals.agencyId).set(agency.toMap());
}

Try returning Future<void> I'm not sure where you are getting Void with a capital V from.

    return new ListView.builder(
                          itemCount: (snapshot.data! as QuerySnapshot).docs.length,
                          itemBuilder: (BuildContext context, int index) {
                            Trxns trxns = Trxns.fromFirestore(
                                snapshot.data.docs[index].data());

The solution as discussed below was to do this:

Trxns trxns = Trxns.fromFirestore((snapshot.data! as QuerySnapshot).docs[index]!.data() as Map<String, dynamic>);

Map<DateTime, List<Event?>> convertToMap(List<Event> item) {
    Map<DateTime, List>? result;

    for (int i = 0; i < item.length; i++) {
      Event data = item[i];
      //get the date and convert it to a DateTime variable
      //DateTime currentDate = DateFormat('MM-dd-yyyy - kk:mm').format(data.eventDate);
      DateTime currentDate = DateTime(data.eventDate!.year, data.eventDate!.month, data.eventDate!.day, data.eventDate!.hour, data.eventDate!.minute);

      List eventNames = [];
      //add the event name to the the eventNames list for the current date.
      //search for another event with the same date and populate the eventNames List.
      for (int j = 0; j < item.length; j++) {
        //create temp calendarItemData object.
        Event temp = item[j];
        //establish that the temp date is equal to the current date
        if (data.eventDate == temp.eventDate) {
          //add the event name to the event List.
          eventNames.add(temp.eventName);
        } //else continue
      }

      //add the date and the event to the map if the date is not contained in the map
      if (result == null) {
        result = {
          currentDate: eventNames
        };
      } else {
        result[currentDate] = eventNames;
      }
      return result as Map<DateTime, List<Event?>>;
    }
  }

I think you meant to put that return statement after the for loop, not inside of it.

thank you for your help. The first and third fixes worked but the second on did not work. I made the changes you suggested and get this error: The getter 'docs' isn't defined for the type 'Object' at lib\screens\agent_dash_board.dart:57:44 . Here is the code now: Trxns? trxns = Trxns.fromFirestore( snapshot.data?.docs[index].data()); — LostTexan, Jun 25 '21 at 17:53
Can you add more context to the code surrounding the second problem? Perhaps you could try `Trxns trxns = Trxns.fromFirestore( (snapshot.data! as QuerySnapshot).docs[index].data());` since it is consistent with with the approach you took for the `itemCount` argument. — mmcdon20, Jun 25 '21 at 18:02
I tried your suggestion and got this error: The argument type 'Object?' can't be assigned to the parameter type 'Map' . Here is the Trxn.fromFirestore() code snippet, Trxns.fromFirestore(Map firestore) : trxnId = firestore['trxnId'], agentId = firestore['agentId']; — LostTexan, Jun 25 '21 at 18:16
is `.data()` meant to return a `Map` ? It appears the `fromFirestore` method expects you to pass a `Map`. Maybe you can cast it to one? like: `Trxns trxns = Trxns.fromFirestore( (snapshot.data! as QuerySnapshot).docs[index]!.data() as Map);` — mmcdon20, Jun 25 '21 at 18:21

I have 3 issues from migrating to null-safety

1 Answers1