winform DataGridView依据光标位置设置所在行的背景颜色

private void gv_CellMouseEnter(object sender, DataGridViewCellEventArgs e)
        {
            if (e.RowIndex != -1)
            {
                object prevIndex = gv.Tag;

                if (prevIndex == null 
------解决方案--------------------------------------------------------
 !prevIndex.Equals(e.RowIndex))
                {
                    gv.Tag = e.RowIndex;
                    gv.Rows[e.RowIndex].DefaultCellStyle.BackColor = Color.Red;
                    gv.Rows[e.RowIndex].DefaultCellStyle.ForeColor = Color.Blue;
                }
            }
        }
        private void gv_CellMouseLeave(object sender, DataGridViewCellEventArgs e)
        {
            if (e.RowIndex != -1)
            {
                gv.Rows[e.RowIndex].DefaultCellStyle.BackColor = Color.White;
                gv.Rows[e.RowIndex].DefaultCellStyle.ForeColor = Color.FromArgb(0, 64, 64);
            }
        }