I’m new to Flutter and facing some difficulties.
I’m building an expense tracking app and trying to implement a database using the sqflite package. However, whenever I attempt to add a new transaction, I get the exception ‘This will throw an exception in the future. For now it is displayed once per type’ in the debug console, and the app freezes. Am I misusing a callback function?
The Relevant code follows:

Here is my DB definition and operations code:

class DbUtil {
  DbUtil._();
  static final DbUtil instance = DbUtil._();
  static Database? _database;

  get database async {
    if (_database != null) return _database;

    _database = await _initDatabase();
    return _database;
  }

  _initDatabase() async {
    return await sql.openDatabase(
      path.join(await sql.getDatabasesPath(), 'transactions.db'),
      version: 1,
      onCreate: _onCreate,
    );
  }

  _onCreate(Database db, int version) async {
    await db.execute(
        'CREATE TABLE transactions (id TEXT PRIMARY KEY, title TEXT, value FLOAT, date DATE ,category TEXT)');
  }

  Future<void> insert(String table, Map<String, Object> data) async {
    final db = await database;
    await db.insert(table, data,
        conflictAlgorithm: sql.ConflictAlgorithm.replace);
  }
}

Next, my main.dart (I removed some code to keep it concise on what is relevant):

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'My Expenses',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<Category>? category;

  final _baseUrl = 'https://expenses-a210d-default-rtdb.firebaseio.com/';

  List<Transact> _transactions = [];

  _openTransactionFormModal(BuildContext context) {
    showModalBottomSheet(
      context: context,
      builder: (_) {
        return TransactionForm(_addTransaction);
      },
    );
  }

  _addTransaction(String title, double value, DateTime date, String category) {
    final newTransaction = Transact(
      id: Random().nextDouble().toString(),
      title: title,
      value: value,
      date: date,
      category: category,
    );
    setState(() {
      _transactions.add(newTransaction);
      _sumTotalCategory(newTransaction);
      _addToDb(newTransaction);
    });

    Navigator.of(context).pop();
  }

  _addToDb(transaction) async {
    await DbUtil.instance.insert(
      'transactions',
      {
        'id': transaction.id,
        'title': transaction.title,
        'value': transaction.value,
        'date': transaction.date,
        'category': transaction.category,
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    final appBar = AppBar(
        title: Text(
          'Despesas Pessoais',
          style: TextStyle(
            fontSize: 20 * MediaQuery.of(context).textScaleFactor,
          ),
        ),
        actions: [
          // IconButton(
          //   onPressed: () => loadTransactions(),
          //   icon: Icon(Icons.refresh),
          // ),
          IconButton(
            onPressed: () => _openTransactionFormModal(context),
            icon: Icon(Icons.add),
          ),
        ]);
    final availableHeight = MediaQuery.of(context).size.height -
        appBar.preferredSize.height -
        MediaQuery.of(context).padding.top;
    return Scaffold(
      appBar: appBar,
      body: SingleChildScrollView(
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            PieChartExpenses(valueSum),
            Container(
              width: double.infinity,
              child: Card(
                color: Color.fromARGB(255, 2, 84, 90),
                elevation: 5,
                child: total_sum(valueSum: valueSum),
              ),
            ),
            Container(
              height: availableHeight * 0.7,
              child: Column(
                children: [
                  TransactionList(_transactions, _removeTransaction),
                ],
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: () => _openTransactionFormModal(context),
      ),
      floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
    );
  }
}

I attempted to modify the insert function based on the solution from this answer, but it didn’t work.
I also tried modifying the function to close the database afterward, but that had no effect either. From what I can tell, the database isn’t even being opened.

After the App freezes, I tried to restart it. The following messages came on the Debug Console:

E/flutter (11237): #24 DbUtil.insert db_util.dart:35 
E/flutter (11237): <asynchronous suspension> 
E/flutter (11237): #25 _MyHomePageState._addToDb main.dart:109 
E/flutter (11237): <asynchronous suspension>

The line 109 on the main.dart is the one containing “transactions”, (third line on the _addToDB function).
The line 35 in db_util.dart is the one that reads await db.insert(table, data, on the insert function.