Getting compile time errors while building Streams in Flutter

Question

I'm trying to return this List as a Stream, but I'm getting the below errors:

1. The body might complete normally, causing 'null' to be returned, but the return type is a potentially non-nullable type.

2. A value of type 'Future<QuerySnapshot<Map<String, dynamic>>>' can't be assigned to a variable of type 'QuerySnapshot<Object?>'.

3. A value of type 'List<dynamic>?' can't be returned from the method 'userBookmarkedCourses' because it has a return type of 'Stream<List<dynamic>?>'.

Listing below is the code that is causing these errors:

  Stream<List<dynamic>?> userBookmarkedCourses() {
    print("User Id within User Provider: $userId");
    QuerySnapshot userSnapshot;
    try {
      if (userId != null) {
        userSnapshot = FirebaseFirestore.instance.collection('users').where('userID', isEqualTo: userId).get();
        if (userSnapshot.docs.isNotEmpty) {
          return coursesBookmarkedList = userSnapshot.docs[0].get('coursesBookmarked');
        }
        return coursesBookmarkedList = [];
      }
    } catch (error) {
      coursesBookmarkedList = [];
    }
  }

I would also like to know how to declare this within the MultiProviders and do I consume it using the Provider.of

I'm new to Streams. What is the cause of this error?

score 1 · Answer 1 · answered Aug 30 '21 at 12:24

1- You have to return something in catch block. Because the method userBookmarkedCourses has a return type.

2- You have to set QuerySnapshot<Map<String, dynamic>> as userSnapshot's type. Additionally, you must put await before FirebaseFirestore.instance.collection('users').where('userID', isEqualTo: userId).get();

3- Return type of method is a Stream<List?>. But, you are returning List<dynamic>?. Either change method's returning type to List<dynamic>? or return a variable which is a Stream<List?>

Getting compile time errors while building Streams in Flutter

1 Answers1