A value of type 'List<Map<String, dynamic>>' can't be assigned to a variable of type 'List<ProjectBoxes>' - flutter

Question

I'm tryng to get a list of boxes to show in a dropdown. But I am can't convert to list map to my object list.
Here's the error message:
A value of type 'List<Map<String, dynamic>>' can't be assigned to a variable of type 'List'.
Try changing the type of the variable, or casting the right-hand type to 'List'.
Here's the code:
import 'package:flutter/material.dart';
import 'package:trfcompactapp/constants.dart';
import '../model/sql_helper.dart';
import '../screens/drawer.dart';
import '../controller/localizationstrf.dart';
class ProjectBoxes {
ProjectBoxes(this.boxId, this.boxName, this.lenght, this.width, this.weight,
this.useLabel, this.labelOrientation, this.createdAt);
int boxId;
String boxName;
int lenght;
int width;
int weight;
int useLabel;
int labelOrientation;
DateTime createdAt;
}
class Project extends StatefulWidget {
const Project({super.key});
#override
State<Project> createState() => _ProjectState();
}
class _ProjectState extends State<Project> {
late ProjectBoxes selectedProjectBox;
#override
void initState() {
super.initState();
_refreshJournals();
}
List<Map<String, dynamic>> _journals = [];
List<Map<String, dynamic>> _journalBoxes = [];
bool _isLoading = true;
// This function is used to fetch all data from the database
void _refreshJournals() async {
final data = await SQLHelper.getProjects();
final dataBoxes = await SQLHelper.getBoxes();
setState(() {
_journals = data;
_isLoading = false;
_journalBoxes = dataBoxes;
boxes = _journalBoxes; // in this line the error happens.
});
}
late List<ProjectBoxes> boxes = <ProjectBoxes>[];
final TextEditingController _projectNameController = TextEditingController();
final TextEditingController _fkProjectBoxController = TextEditingController();
final TextEditingController _fkProjectPalletController =
TextEditingController();
final TextEditingController _fkProjectRobotController =
TextEditingController();
void _showForm(int? id) async {
if (id != null) {
final existingJournal =
_journals.firstWhere((element) => element['projectId'] == id);
final existingJournalBox = _journalBoxes.firstWhere(
(element) => element['boxId'] == existingJournal['FK_project_box']);
_projectNameController.text = existingJournal['projectName'];
_fkProjectBoxController.text =
existingJournalBox['FK_project_box'].toString();
_fkProjectPalletController.text =
existingJournal['FK_project_pallet'].toString();
_fkProjectRobotController.text =
existingJournal['FK_project_robot'].toString();
selectedProjectBox = existingJournalBox[0];
boxes = existingJournalBox[0];
}

Answer 1

It trys to assign List<Map> to a List. You'll have to write a converter to convert the data inside the Map to new ProjectBoxes objects.
Instead of boxes = _journalBoxes; use the following loop:
for (Map<String, dynamic> item in _journalBoxes) {
boxes.add(ProjectBoxes(
field1: item["firstField"] ?? "default value",
field2: item["thirdField"],
field3: item["secondField"] ?? false,
));
}
I don't know the structure of ProjectBoxes so I added some example values:
class ProjectBoxes {
// example fields
String field1;
int? field2;
bool field3;
// constructor
ProjectBoxes({
required this.field1,
this.field2,
required this.field3,
});
}