我试图从mysql数据库中获取值，我创建了一个单独的类，以便为我的队友创建一个更好的概述。
在课堂上我有这样的代码：

public void missingOverview()
    {
        //missing items ophalen
        //connectie opzetten
        MySqlConnectionStringBuilder connectionStr = new MySqlConnectionStringBuilder
        {
            Server = "localhost",
            Database = "GIPLouisThuyttenGregoireRobbe",
            UserID = "root",
            Password = "usbw",
            ConnectionTimeout = 60,
            Port = 3307,
            AllowZeroDateTime = true
        };
        MySqlConnection MySqlCon = new MySqlConnection(connectionStr.ConnectionString);

        //connectie aanmaken en query aanvragen
        try
        {
            //checken of de connectiestatus open of gesloten is, en zet deze open indien gesloten
            if (MySqlCon.State == System.Data.ConnectionState.Closed)
                MySqlCon.Open();
            //query aanvragen
            String query = "SELECT Username FROM login";
            MySqlCommand sqlCmd = new MySqlCommand(query, MySqlCon);

            MySqlDataReader reader = sqlCmd.ExecuteReader();

            while (reader.Read())
            {
                app.lsbMissingOverview.Items.Add(reader.GetString("Username"));
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
        MySqlCon.Close();
    }

在我的窗口里有这样的代码：

private void btnOverview_Click(object sender, RoutedEventArgs e)
    {
        //overview toevoegen
        Overview overviewClass = new Overview();
        overviewClass.missingOverview();}

当按下按钮时，没有值显示，有人知道为什么吗？