求助，关于一个继承类的问题

Question

写了一个combobox继承类GridCombobox，实现了在下拉列表中加了一个DataGridView，如下：
class GridCombobox:ComboBox
    {
            ToolStripControlHost GriddataHost;
            ToolStripDropDown dropDown;            public GridCombobox()
            {
                DataGridView dataGrid = new DataGridView();
                GriddataHost = new ToolStripControlHost(dataGrid);
                dropDown = new ToolStripDropDown();
                dropDown.Items.Add(GriddataHost);
                
            }
            public DataGridView DataGridView
            {
                get { return GriddataHost.Control as DataGridView; }
            }
            
            private void ShowDropDown()
            {
               if (dropDown != null)
                {
                   GriddataHost.Size = new Size(DropDownWidth-10, DropDownHeight+10);
                   dropDown.Show(this, 0, this.Height);
                }
            }
            protected override void WndProc(ref Message m)
            {
                if (m.Msg == WM_LBUTTONDBLCLK || m.Msg == WM_LBUTTONDOWN)
                {
                        ShowDropDown();
                        return;
                }
                base.WndProc(ref m);
            }
}
//请问怎么修改弹出下拉的宽度呢？？？