Check if Key Exists in NameValueCollection

Question

Is there a quick and simple way to check if a key exists in a NameValueCollection without looping through it?

Looking for something like Dictionary.ContainsKey() or similar.

There are many ways to solve this of course. Just wondering if someone can help scratch my brain itch.

Answer 1

In VB it's:

if not MyNameValueCollection(Key) is Nothing then
.......
end if

In C# should just be:

if (MyNameValueCollection(Key) != null) { }

Not sure if it should be null or "" but this should help.

Answer 2

I am using this collection, when I worked in small elements collection.

Where elements lot, I think need use "Dictionary". My code:

NameValueCollection ProdIdes;
string prodId = _cfg.ProdIdes[key];
if (string.IsNullOrEmpty(prodId))
{
    ......
}

Or may be use this:

 string prodId = _cfg.ProdIdes[key] !=null ? "found" : "not found";

Answer 3

If the collection size is small you could go with the solution provided by rich.okelly. However, a large collection means that the generation of the dictionary may be noticeably slower than just searching the keys collection.

Also, if your usage scenario is searching for keys in different points in time, where the NameValueCollection may have been modified, generating the dictionary each time may, again, be slower than just searching the keys collection.

Answer 4

NameValueCollection n = Request.QueryString;

if (n.HasKeys())
   {
       //something
   }

Return Value Type: System.Boolean true if the NameValueCollection contains keys that are not null; otherwise, false. LINK

Answer 5

Use this method:

private static bool ContainsKey(NameValueCollection collection, string key)
{
    if (collection.Get(key) == null)
    {
        return collection.AllKeys.Contains(key);
    }

    return true;
}

It is the most efficient for NameValueCollection and doesn't depend on does collection contain null values or not.

Answer 6

I don't think any of these answers are quite right/optimal. NameValueCollection not only doesn't distinguish between null values and missing values, it's also case-insensitive with regards to it's keys. Thus, I think a full solution would be:

public static bool ContainsKey(this NameValueCollection @this, string key)
{
    return @this.Get(key) != null 
        // I'm using Keys instead of AllKeys because AllKeys, being a mutable array,
        // can get out-of-sync if mutated (it weirdly re-syncs when you modify the collection).
        // I'm also not 100% sure that OrdinalIgnoreCase is the right comparer to use here.
        // The MSDN docs only say that the "default" case-insensitive comparer is used
        // but it could be current culture or invariant culture
        || @this.Keys.Cast<string>().Contains(key, StringComparer.OrdinalIgnoreCase);
}