如何在ASP.NET中检查Request.QueryString是否具有特定值？

Question

I have an error.aspx page. If a user comes to that page then it will fetch the error path in page_load() method URL using Request.QueryString["aspxerrorpath"] and it works fine.

But if a user directly accesses that page the it will generate an exception because aspxerrorpath is not there.

How can I check that aspxerrorpath is there or not?

Answer 1

You can just check for null :

if(Request.QueryString["aspxerrorpath"]!=null)
{
   //your code that depends on aspxerrorpath here
}

Answer 2

Check for the value of the parameter:

// .NET < 4.0
if (string.IsNullOrEmpty(Request.QueryString["aspxerrorpath"]))
{
 // not there!
}

// .NET >= 4.0
if (string.IsNullOrWhiteSpace(Request.QueryString["aspxerrorpath"]))
{
 // not there!
}

If it does not exist, the value will be null , if it does exist, but has no value set it will be an empty string.

I believe the above will suit your needs better than just a test for null , as an empty string is just as bad for your specific situation.

Answer 3

To check for an empty QueryString you should use Request.QueryString.HasKeys property.

To check if the key is present: Request.QueryString.AllKeys.Contains()

Then you can get ist's Value and do any other check you want, such as isNullOrEmpty, etc.

Answer 4

You can also try:

if (!Request.QueryString.AllKeys.Contains("aspxerrorpath"))
   return;

Answer 5

string.IsNullOrEmpty(Request.QueryString["aspxerrorpath"]) //true -> there is no value

如果有值将返回

Answer 6

那更直接的方法呢？

if (Request.QueryString.AllKeys.Contains("mykey")

Answer 7

think the check you're looking for is this:

if(Request.QueryString["query"] != null) 

It returns null because in that query string it has no value for that key.

Answer 8

To resolve your problem, write the following line on your page's Page_Load method.

if (String.IsNullOrEmpty(Request.QueryString["aspxerrorpath"])) return;

.Net 4.0 provides more closer look to null, empty or whitespace strings, use it as shown in the following line:

if(string.IsNullOrWhiteSpace(Request.QueryString["aspxerrorpath"])) return;

This will not run your next statements (your business logics) if query string does not have aspxerrorpath.