你调用的对象是空的。在查询字符串中 [英] Object reference not set to an instance of an object. in query string

问题描述

请一些人说明为什么会发生这个错误对象引用未设置为object.in此代码的实例。在此行中发生错误

string blog_title = Request.QueryString [blog_title ] .ToString（）;

Pls some one tell that why this error is occurred Object reference not set to an instance of an object.in this code.in this line the error occurred
string blog_title = Request.QueryString[blog_title].ToString();

if (!IsPostBack)
{
   //blog_title = Session["blog_title"].ToString();
   string blog_title = Request.QueryString["blog_title"].ToString();

   if (Request.QueryString["blog_title"] != null)
   {
      try
      {
         blog_title = (Request.QueryString["blog_title"]);
      }
      catch
      {
         // deal with it
         Response.Redirect("blog/Default.aspx");
      }
   }
   list_bind();
   frm_bind();
}

推荐答案

简单：没有名称在变量中的QueryString blog_title

您的意思是写：

Simple: there is no QueryString with the name that is in teh variable blog_title
Did you mean to write:

string blog_title = Request.QueryString["blog_title"].ToString();

而不是

Instead of

string blog_title = Request.QueryString[blog_title].ToString();

在请求查询字符串时，在将值传递给它之前它不会成为对象，并且确认该值存在，此时它变为一个有效的对象。



例如，

When requesting a querystring, it doesn''t become an object until the value is passed to it, and the value is confirmed to exist, at that point it becomes a valid object.

So for example,

httpcontext.current.request.querystring("apple") 

在确认苹果存在之前无效



所以你先测试苹果的存在，然后问佛r值为



在vb中，不确定在c＃

is not valid until the existence of apple is confirmed

So you test for the existance of apple first, and then ask for the value

in vb its, not sure in c#

if not (httpcontext.current.request.querystring("apple") is nothing) then
 ''The object surely exist, so get the value now
 Dim apples as string = httpcontext.current.request.querystring("apple")
end if

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