error: The argument type 'StreamTransformer<dynamic, dynamic>' can't be assigned to the parameter type 'StreamTransformer<QuerySnapshot*, List<Todo>>

Question

I keep getting this error in my code for firebase, I am using a stream list and it produces this error when calling from the map.

How can I resolve this?

error: The argument type 'StreamTransformer<dynamic, dynamic>' can't be assigned to the parameter type 'StreamTransformer<QuerySnapshot*, List>

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:new_todo_list_shopping/model/todo.dart';
import 'package:new_todo_list_shopping/utils.dart';

class FirebaseApi {
  static Future<String> createTodo(Todo todo) async {
    final docTodo = FirebaseFirestore.instance.collection('todo').doc();

    todo.id = docTodo.id;
    await docTodo.set(todo.toJson());

    return docTodo.id;
  }

  static Stream<List<Todo>> readTodos() => FirebaseFirestore.instance
      .collection('todo')
      .orderBy(TodoField.createdTime, descending: true)
      .snapshots()
      .transform(Utils.transformer(Todo.fromJson));

  static Future updateTodo(Todo todo) async {
    final docTodo = FirebaseFirestore.instance.collection('todo').doc(todo.id);

    await docTodo.update(todo.toJson());
  }

  static Future deleteTodo(Todo todo) async {
    final docTodo = FirebaseFirestore.instance.collection('todo').doc(todo.id);

    await docTodo.delete();
  }
}

Answer 1

update the return type of transformer fucntion. I was also facing same issue, you can use the transformer method code below:

static StreamTransformer<QuerySnapshot<Map<String, dynamic>>, List<T>> transformer<T>(
          T Function(Map<String, dynamic> json) fromJson) =>
      StreamTransformer<QuerySnapshot<Map<String, dynamic>>, List<T>>.fromHandlers(
        handleData: (QuerySnapshot<Map<String, dynamic>>  data, EventSink<List<T>> sink) {
          final snaps = data.docs.map((doc) => doc.data()).toList();
          final objects = snaps.map((json) => fromJson(json as Map<String, dynamic>)).toList();

          sink.add(objects);
        },
      );