C#中如何计算时间差?

C#中怎么计算两时间相差多少。计算2个时间之间的差,可以计算到时分秒!

<1>
label1.Text = "2004-1-1 15:36:05";
label2.Text = "2004-3-1 20:16:35";
DateTime d1 =new DateTime(2004,1,1,15,36,05);
DateTime d2 =new DateTime(2004,3,1,20,16,35);

TimeSpan d3 = d2.Subtract(d1);

label3.Text = "相差:"
+d3.Days.ToString()+"天"
+d3.Hours.ToString()+"小时"
+d3.Minutes.ToString()+"分钟"
+d3.Seconds.ToString()+"秒";

结果如图:



<2>
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DateTime dt1 = Convert.ToDateTime("2009-07-31 00:00:00");
            DateTime dt2 = Convert.ToDateTime("2009-08-02 00:00:00");
            this.Label1.Text = this.DateDiff(dt1,dt2);
        }
    }
    private string DateDiff(DateTime DateTime1, DateTime DateTime2)
    {
        string dateDiff = null;
        try
        {
            TimeSpan ts1 = new TimeSpan(DateTime1.Ticks);
            TimeSpan ts2 = new TimeSpan(DateTime2.Ticks);
            TimeSpan ts = ts1.Subtract(ts2).Duration();
            dateDiff = ts.Days.ToString() + "天" + ts.Hours.ToString() + "小时" + ts.Minutes.ToString() + "分钟" + ts.Seconds.ToString() + "秒";
        }
        catch
        { }
        return dateDiff;
    }

<3>
            string st1 = "14:16";
            string st2 = "14:14";
            DateTime dt1 = Convert.ToDateTime(st1);
            DateTime dt2 = Convert.ToDateTime(st2);
           
            int result = DateTime.Compare(dt1, dt2);
    如果st1的时间大于st2  , result = 1
    如果相等就等于0，
     如果小于就是-1