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";

<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