求一个简单问题，高手指点阿~~~

Question

if (Request.QueryString["id"] != null)
            {
                int ProgramID =Convert.ToInt32(Request.QueryString["id"]);
                program isdate = new program(ProgramID);
                dayList.Text = isdate.Intraday;
                daysta.Value = isdate.StartTime.ToShortDateString().ToString();
                TextBox7.Text = isdate.StartTime.ToLongTimeString().ToString();
                TextBox8.Text = isdate.EndTime.ToLongTimeString().ToString();
                TextBox1.Text = isdate.ProgramName;
                TextBox3.Text = isdate.EmceeName;
                TEXTAREA1.Value = isdate.ProgramIntro;
            }插入断点测试，Request.QueryString["id"] =8
但是int ProgramID =Convert.ToInt32(Request.QueryString["id"]);ProgramID =0？？？怎么回事？？
为什么会这样啊？