提示"未将对象引用设置到对象的实例。“

Question

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string post1 = Request.Form["title"].ToString();
        string post2 = Request.Form["context"].ToString();
        TextBox1.Text = post1;
        TextBox2.Text = post2;
    }
}
这程序我输进去有时可以运行有时不行，不行时提示未将对象引用设置到对象的实例。
也不需要空间引用，也不需要什么new ，为什么书上都这么写，但实际不能运行？

Answer 1

加个判断
if(Request.Form["title"]!=null)
  string post1 = Request.Form["title"].ToString();if(Request.Form["context"]!=null)
  string post2 = Request.Form["context"].ToString();

Answer 2

   if(Request.Form["year"]!=null)
        {
        string post1 = Request.Form["year"].ToString();
        }
        if(Request.Form["month"]!=null)
        {
            string post2 =Request.Form["month"].ToString();
        }
            if(Request.Form["day"]!=null)
            {
                string post3 =Request.Form["day"].ToString();
            }
            if (Request.Form["hour"] != null)
            {
                string post4 = Request.Form["hour"].ToString();
            }
                    string hebing;
                    hebing = post1 + post2 + post3 + post4;
                    TextBox4.Text = hebing;
改成这样的话就hebing = post1 + post2 + post3 + post4;说找不到post1了

Answer 3

string post1="";
if(Request.Form["year"]!=null)
         {
          post1= Request.Form["year"].ToString();
         }        string post2="";
         if(Request.Form["month"]!=null)
         {
             post2 =Request.Form["month"].ToString();
         }            string post3="";
             if(Request.Form["day"]!=null)
             {
                 post3 =Request.Form["day"].ToString();
             }
             
             string post4="";
             if (Request.Form["hour"] != null)
             {
                 post4 = Request.Form["hour"].ToString();
             }
                     string hebing;
                     hebing = post1 + post2 + post3 + post4;
                     TextBox4.Text = hebing;