DataGridView实现多表头，高效处理rowSpan

单独建一个类：
public class DGVHeaderUnite
    {
        public string rowValue;//重新绘制的文本框内容
        public int col1Height, col2Height;//第一行行高，第二行行高

        private static SortedList rowSpan = new SortedList();//取得需要重新绘制的单元格
        private static SortedList valueList = new SortedList();

        /// <summary>
        /// 
        /// DataGridView合并单元格(横向)
        /// </summary>
        /// <param name="dgv">绘制的DataGridview </param>
        /// <param name="cellArgs">绘制单元格的参数（DataGridview的CellPainting事件中参数）</param>
        /// <param name="minColIndex">起始单元格在DataGridView中的索引号</param>
        /// <param name="maxColIndex">结束单元格在DataGridView中的索引号</param>
        /// <param name="UniteValue">重新绘制的文本框内容</param>
        public void MerageRowSpan(DataGridView dgv, DataGridViewCellPaintingEventArgs cellArgs, int minColIndex, int maxColIndex)
        {
            if (cellArgs.ColumnIndex < minColIndex || cellArgs.ColumnIndex > maxColIndex) return;

            Rectangle rect = new Rectangle();

            if (rowSpan[cellArgs.ColumnIndex] == null)
            {
                //首先判断当前单元格是不是需要重绘的单元格
                //保留此单元格的信息，并抹去此单元格的背景
                rect.X = cellArgs.CellBounds.X;
                rect.Y = cellArgs.CellBounds.Y;

                rect.Width = cellArgs.CellBounds.Width;
                rect.Height = cellArgs.CellBounds.Height;

                rowSpan.Add(cellArgs.ColumnIndex, rect);
                valueList.Add(cellArgs.ColumnIndex, cellArgs.Value.ToString());

                if (cellArgs.ColumnIndex == maxColIndex)
                    MeragePrint(dgv, cellArgs, minColIndex, maxColIndex);
            }
            else
            {
                IsPostMerage(dgv, cellArgs, minColIndex, maxColIndex);
            }
        }

        /// <summary>
        /// 不是初次单元格绘制
        /// </summary>
        /// <param name="dgv"></param>
        /// <param name="cellArgs"></param>
        /// <param name="minColIndex"></param>
        /// <param name="maxColIndex"></param>
        public void IsPostMerage(DataGridView dgv, DataGridViewCellPaintingEventArgs cellArgs, int minColIndex, int maxColIndex)
        {
            //比较单元是否有变化
            Rectangle rectArgs = (Rectangle)rowSpan[cellArgs.ColumnIndex];
            if (rectArgs.X != cellArgs.CellBounds.X || rectArgs.Y != cellArgs.CellBounds.Y
                || rectArgs.Width != cellArgs.CellBounds.Width || rectArgs.Height != cellArgs.CellBounds.Height
                || valueList[cellArgs.ColumnIndex] != cellArgs.Value.ToString())
            {