this之写扩展方法

this之写扩展方法

   public static class MathExtence
    {
        /// <summary>
        /// double类型四舍五入
        /// </summary>
        /// <param name="doubleNum"></param>
        /// <returns></returns>
        public static int Round(this double doubleNum)//这里的this double 是写double的扩展方法
        {
            int roundNum=Math.Round(doubleNum,2)%1>=0.5?1:0;
            return (int)(Math.Round(doubleNum + roundNum,1));
        }
    }