This code works in the sample, Grid\Samples\Quick Start\ComboBoxBaseGridDemo, to set the width of the dropdown.
private void comboBoxBase1_DropDown(object sender, System.EventArgs e)
{
this.textLog.Text += "Event: DropDown\r\n";
this.comboBoxBase1.PopupContainer.Width = this.gridListControl1.Grid.Model.ColWidths.GetTotal(0, this.gridListControl1.Grid.Model.ColCount) + 4 + SystemInformation.VerticalScrollBarWidth;
}
>/pre>