Winform 自定义控件不允许, 禁止修改高度, 类似TextBox，只能横向调整宽度

// 添加引用 System.Desing;

using System.Windows.Forms;
using System.Windows.Forms.Design;

namespace WindowsFormsApp2
{
    // 引用 System.Design
    /// <summary>
    /// 自定义控件不允许更改高度
    /// </summary>
    [System.ComponentModel.Designer(typeof(Designer1))]
    public partial class UserControl1 : UserControl
    {
        public UserControl1()
        {
            InitializeComponent();
        }
    }

    #region 自定义设计类
    /// <summary>
    /// 自定义设计类
    /// </summary>
    public class Designer1 : System.Windows.Forms.Design.ControlDesigner
    {
        /// <summary>
        /// 不允许调整控件的高度
        /// </summary>
        public override SelectionRules SelectionRules
        {
            get
            {
                SelectionRules rules = SelectionRules.Visible | SelectionRules.Moveable |
                    SelectionRules.LeftSizeable | SelectionRules.RightSizeable;

                return rules;
            }
        }
    }
    #endregion
}