string values = this.txtFormat.Text;
string [] aa = values.Split('-');
if(aa.Length == 3)
MessageBox.Show("转换后为："+aa[0]+aa[1]+aa[2]);
逆操作：
if (value.Length <8) return "";
return value.Substring(0,4) + "-" + value.Substring(4,2) + "-" + value.Substring(6,2);
或者：
private static string FormatDate(string value)
{
if (value.Trim() == "") return "";
int year = 0;
int month = 0;
int day = 0;
char[] separator = new char[4];
separator[0] = '-';
separator[1] = '.';
separator[2] = ',';
separator[3] = ':';
string[] sDate = value.Split(separator);
switch (sDate.Length)
{
case 3:
year = SXConvert.ToInt32(sDate[0]);
month = SXConvert.ToInt32(sDate[1]);
day = SXConvert.ToInt32(sDate[2]);
break;
case 2:
year = DateTime.Now.Year;
month = SXConvert.ToInt32(sDate[0]);
day = SXConvert.ToInt32(sDate[1]);
break;
case 1:
year = DateTime.Now.Year;
month = DateTime.Now.Month;
day = SXConvert.ToInt32(sDate[0]);
break;
}
// 用来检测数据是否是一个合法的日期值
   Convert.ToDateTime(year.ToString() + "-" + month.ToString() + "-" + day.ToString());
return AddZero(year,4) + "-" + AddZero(month,2) + "-" + AddZero(day,2);
}
private static string AddZero(int value,int length)
{
string temp = value.ToString();
for (int i=length - temp.Length;i>0;i--)
{
temp = "0" + temp;
}
return temp;
}