当前路径：Cool.Windows.Forms/CoolMenuButton.cs
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Cool.Windows.Forms
{
    public class CoolMenuButton : Label
    {
        public CoolMenuButton()
        {
            this.DoubleBuffered = true;//设置本窗体
            this.SetStyle(
                      //ControlStyles.UserPaint |    //使用自定义的绘制方式
                      ControlStyles.ResizeRedraw//当控件大小发生变化时就重新绘制
                    | ControlStyles.SupportsTransparentBackColor//则控件接受 alpha 组件数小于 255 个的 BackColor 来模拟透明度
                    | ControlStyles.AllPaintingInWmPaint//则控件忽略窗口消息 WM_ERASEBKGND 以减少闪烁
                    | ControlStyles.OptimizedDoubleBuffer//则控件将首先绘制到缓冲区而不是直接绘制到屏幕，这可以减少闪烁
                    | ControlStyles.DoubleBuffer
                    , true);
            this.Dock = DockStyle.Top;
            this.Height = 30;
            this.AutoSize = false;
            this.BackColor = Color.FromArgb(0, 163, 129);
            this.Cursor = Cursors.Hand;
            _image = Properties.Resources.Menu1;
            _expandImage = Properties.Resources.Expand_Bottom;

            expandRect = new Rectangle(this.Width - 25, (this.Height - 9) / 2, 9, 9);
        }

        #region 属性
        [System.ComponentModel.Browsable(true)]
        public int Index { get; set; }

        private Color _backColor;
        [System.ComponentModel.Browsable(true)]
        [System.ComponentModel.DefaultValue(typeof(Color), "")]
        public new Color BackColor
        {
            get => _backColor;
            set
            {
                _backColor = value;
                this.Invalidate();
            }
        }

        private I...