组合框.Parent = this;
            组合框.Items.AddRange(new object[] { "111", "222", "333", "444" });
            组合框.DropDownHeight = 1;
            组合框.SelectedIndex = 0;
            //组合框.DropDownStyle = ComboBoxStyle.Simple;

            ComboBox 组合框 = new ComboBox();
            List<string> aaa = new List<string>();
            int aaaa = 0; while (++aaaa < 10) aaa.Add(aaaa.ToString());
            组合框.DataSource = aaa;
            组合框.Parent = this;
            //组合框.Items.AddRange(new object[] { "111", "222", "333", "444" });
            //组合框.DropDownHeight = 1;
            组合框.SelectedIndex = 0;
            //组合框.DropDownStyle = ComboBoxStyle.Simple;

缘由https://bbs.csdn.net/topics/395430686