You can change the size of the dropdown in this event. Is this what you wanted?
private void comboBoxExt1_DropDown(object sender, System.EventArgs e)
{
this.comboBoxExt1.PopupContainer.Width = 1200;
}
Or, are you trying to change the colwidth of a column in the GridListControl. If so, you would have to handle the QueryColWidth event on the embedded Grid.
this.gridListControl1.Grid.QueryColWidth += new GridRowColSizeEventHandler(grid_QueryColWidth);
void grid_QueryColWidth(object sender, GridRowColSizeEventArgs e)
{ //size col 2
if(e.Index == 2)
{
e.Size = 400;
e.Handled = true;
}
}