I've seen a couple examples of how to check if a query string exists in a url with C#:
www.site.com/index?query=yes
if(Request.QueryString["query"]=="yes")
But how would I check a string without a parameter? I just need to see if it exists.
www.site.com/index?query
if(Request.QueryString["query"] != null) //why is this always null?
I know there's probably a simple answer and I'll feel dumb, but I haven't been able to find it yet. Thanks!
You cannot use a null check to determine if a key exists when the "=" is not supplied since null means that the key wasn't in the query string.
The problem is that "query" is being treated as a value with a null key and not as a key with a null value.
In this case the key is also null inside Request.QueryString.AllKeys.
I used this generic method to "fix" the null key problem in the query string before using it. This doesn't involve manually parsing the string.
Usage example:
var fixedQueryString = GetFixedQueryString(Request.QueryString);
if (fixedQueryString.AllKeys.Contains("query"))
{
}
The method:
public static NameValueCollection GetFixedQueryString(NameValueCollection originalQueryString)
{
var fixedQueryString = new NameValueCollection();
for (var i = 0; i < originalQueryString.AllKeys.Length; i++)
{
var keyName = originalQueryString.AllKeys[i];
if (keyName != null)
{
fixedQueryString.Add(keyName, originalQueryString[keyName]);
}
else
{
foreach (var keyWithoutValue in originalQueryString[i].Split(','))
{
fixedQueryString.Add(keyWithoutValue, null);
}
}
}
return fixedQueryString;
}