从数据库中获取价值并将其放入文本框中

Question

我完全没有编程，我正在学习，类，方法与mysql的连接。

所以我有一个名为take的类，我有一个从数据库表中获取最后一个值的方法。

namespace Budget
{
    class take
    {
        private MySqlConnection connection;
        private string datasource;
        private string port;
        private string username;
        private string password;
        public take()
        {
            Initialize();
        }
        private void Initialize()
        {
            datasource = "localhost";
            port = "3306";
            username = "root";
            password = "root";
            string connectionString;
            connectionString = "DATASOURCE=" + datasource + ";" + "PORT=" + port + ";" + "USERNAME=" + username + ";" + "PASSWORD=" + password + ";";

            connection = new MySqlConnection(connectionString);
        }
        private bool OpenConnection()
        {
            connection.Open();
            return true;
        }
        private bool CloseConnection()
        {
            connection.Close();
            return true;
        }
        public decimal budget()
        {
            string query =
              @"SELECT balance 
              FROM history 
              ORDER BY id DESC 
              LIMIT 1 ";
            if (this.OpenConnection() == true)
            {
                MySqlCommand cmd = new MySqlCommand(query, connection);
                using (var reader = cmd.ExecuteReader())
                {
                    if (reader.Read())
                        return Convert.ToDecimal(reader.GetValue(0));
                    else
                        return 0m;
                }
            }
            else
                return 0m;
        }
    }
}

我想把这个值放在我的主Form FormBox中。但是当我在主要主要表格中写作时

 take.balance();

  

警告警告1永远不会将字段Budget.Form1.take分配给，并且始终具有默认值null

所以问题是，我如何将数据库中的值放到我的主要Form文本框中？