[方法]按日期测试时间跨度问题--时间差(小时,分钟,秒)

在处理工时的时候需要这样处理问题.
启动时间  结束时间 就需要处理多少小时,多少分钟等
写了一个函数处理  

protected decimal GetSpanTime(TextBox txtstarttime,TextBox txtendtime) 
    {

        int year = int.Parse(txtstarttime.Text.ToString().Substring(0,4));
        int month = int.Parse(txtstarttime.Text.ToString().Substring(4,2));
        int day = int.Parse(txtstarttime.Text.ToString().Substring(6,2));
        int hour = int.Parse(txtstarttime.Text.ToString().Substring(8,2));
        int min = int.Parse(txtstarttime.Text.ToString().Substring(10,2));
        int second = int.Parse(txtstarttime.Text.ToString().Substring(12,2));

        int year2 = int.Parse(txtendtime.Text.ToString().Substring(0,4));
        int month2 = int.Parse(txtendtime.Text.ToString().Substring(4,2));
        int day2 = int.Parse(txtendtime.Text.ToString().Substring(6,2));
        int hour2 = int.Parse(txtendtime.Text.ToString().Substring(8,2));
        int min2 = int.Parse(txtendtime.Text.ToString().Substring(10,2));
        int second2 = int.Parse(txtendtime.Text.ToString().Substring(12,2));

        DateTime t1 = new DateTime(year,month,day,hour,min,second);
        DateTime t2 = new DateTime(year2,month2,day2,hour2,min2,second2);
        TimeSpan diff = t2 - t1;
        decimal h = decimal.Parse(diff.Minutes.ToString()) / 60;
        decimal h2 = decimal.Round(h,4);

        return h2;

    }