I have a custom combo box class that inherits UltraCombo. I need it to display data from a database query. I have verified that the data is in fact being retrieved (i.e. I can print the query results on the console from the method that is supposed to populate the form). No matter what I do, the control does not display the data. The control is part of the Controls collection, as it is visible when running the app. Everything I have seems to comply with the documentation, but it just doesn't work.

Here is my code: 

Main form class:

public partial class SaveLayoutTestForm : Form
{
    public CurrentLayoutControl currentLayoutControl;

    public SaveLayoutTestForm()
    {
        this.currentLayoutControl = new CurrentLayoutControl();
        PopulateLayoutCombo();
    }

    public void PopulateLayoutCombo()
    {
        DataTable layouts = currentLayoutControl.LoadUserGridLayouts(connectionString);
        currentLayoutControl.DataSource = layouts;
        currentLayoutControl.ValueMember = "User_Grid_Layout_Id";
        currentLayoutControl.DisplayMember = "User_Grid_Layout";
    }
}

CurrentLayoutControl class:

public class CurrentLayoutControl : UltraCombo
{
    public DataTable LoadUserGridLayouts(string connString)
    {
        DataTable dataTable = new DataTable();
        SqlConnection conn = new SqlConnection(connString);
        string sql = "USE my_database; SELECT User_Grid_Layout_Id, User_Grid_Layout FROM app.User_Grid_Layouts";
        SqlCommand command = new SqlCommand(sql, conn);

        conn.Open();
        dataTable = ExecuteQuery(connString, command);
        conn.Close();
        return dataTable;
    }

    private DataTable ExecuteQuery(string connString, SqlCommand command)
    {
        DataTable dataTable = new DataTable();
        SqlDataAdapter adapter = new SqlDataAdapter(command);
        adapter.Fill(dataTable);
        return dataTable;

    }
}

Thank you for any help, I really appreciate it.