datetime判断是否为空值的问题

日期型类型判断是否为空，空值插入和修改

                DateTime PM;
                if (this.txtpm.Text != "" && this.txtpm.Enabled == true)
                {
                    PM = Convert.ToDateTime(this.txtpm.Text);
                }
                else
                {
                    PM = DBNull.Value;
                }

报错：Object cannot be cast from DBNull to other types.

PM申明为object，不要指定DateTime类型，你的存储过程参数值也只是接收object对象，只要格式正确就行了