Collections in C#: NameValueCollection

In doing some reading I ran across a handy collection called the NameValueCollection. This collection, which resides in the System.Collections.Specialized namespace, allows you to use either a string or an integer index for the key. Further, it allows you to store more than one string value in a key.

Let’s start the code example by creating a simple Console application. I added using references to System.Collections and System.Collections.Specialized namespaces at the top. As a final bit of housekeeping, make sure to add a Console.ReadLine() as the last line of our code, so the console will wait on us to hit the enter key after we read the results. (If you don’t, the program will run so fast you won’t be able to appreciate your fine work.)

Now I’m going to load some data into a new collection called myCollection. For the data, I’ll use a website owner and the website or sites they own.

      System.Collections.Specialized.NameValueCollection myCollection

        = new System.Collections.Specialized.NameValueCollection();

 

      myCollection.Add(“Arcane”, http://arcanecode.com”);

      myCollection.Add(“PWOP”, http://dotnetrocks.com”);

      myCollection.Add(“PWOP”, http://dnrtv.com”);

      myCollection.Add(“PWOP”, http://www.hanselminutes.com”);

      myCollection.Add(“TWIT”, http://www.twit.tv”);

      myCollection.Add(“TWIT”, http://www.twit.tv/SN”);

Next, I’d like to get some data back out. I mentioned you could cycle through the collection using an integer index, so let’s see how that’s done:

      Console.WriteLine(“Key / Value Pairs by Integer Index”);

      for (int i = 0; i < myCollection.Count; i++)

      {

        Console.WriteLine(i.ToString() + ” “

          + myCollection.GetKey(i) + “: “

          + myCollection.Get(i));

      }

 

[Picture of Key/Value pairs by Integer Index]

 

In the above output you can see how I use the GetKey and Get methods to retrieve the key name and value for that key using the loop’s index. Note that when multiple values are associated with a single key, they are returned as a list of comma separated values.

You can also use foreach logic to cycle through the collection. Here I am using the AllKeys property of our collection to get the list of keys. I can then print the key, and also use the key as the indexer into my collection as you can see below.

      Console.WriteLine();

      Console.WriteLine(“Keys / Value Pairs via AllKeys Collection”);

      foreach (string myKey in myCollection.AllKeys)

      {

        Console.WriteLine(myKey + “: “ + myCollection[myKey]);

      }

 

[Picture of Key/Value pairs via AllKeys Collection]

 

Now I, what? Yes, you in the back row, what was your question? Ah, you say lists of comma separated values are OK, but you want to be able to access individual values? Fortunately some nested looping and the GetValues method will satisfy you demanding types.

 

      Console.WriteLine();

      Console.WriteLine(“Keys / Individual Values”);

      foreach (string myKey in myCollection.AllKeys)

      {

        foreach (string myValue in myCollection.GetValues(myKey))

        {

          Console.WriteLine(myKey + “: “ + myValue);

        }

      }

 

[Picture of Keys/Individual Values]

 

This also works great if your data has commas within it. Let’s add two lines back at the top of the program to the collection.

      myCollection.Add(“CommaTest”, “Here is a , in a string”);

      myCollection.Add(“CommaTest”, “Here is another , in a string”);

 
Now run the application again, and lets look at the results.
 
[Picture of Comma Test]

As you can see in the last area “Keys / Individual Values” the GetValues method correctly determined that the commas I had embedded were part of the data and not a delimiter between values.

Whenever you need a good string collection that has the ability to tie multiple values to a single key, the NameValueCollection would be a good class to take a look at.

 

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7 Responses to “Collections in C#: NameValueCollection”

  1. Rajiv Says:

    Ok, How about sorting the values of a given key alphabetically and then display. For Ex:

    mcol.Add(“Red”, “Sizzling”)
    mycol.Add(“Red”, “Ravishing”)

    I want my values for each key be displayed alphabetically

    i.e

    Red: Ravishing
    Red: Sizzling

  2. GeorgeBR Says:

    Thanks for this – a good down-to-earth reference (unlike the MSDN description of NameValueCollection which documents everything but doesn’t actually help much!) Thanks!

  3. mike Says:

    Outstanding!!

  4. Randall Sexton Says:

    Great post. Thank you much.

  5. Sunil Prasad Says:

    Nice article helped me lot

  6. SyncroMax Says:

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    weblog. Is this a paid theme or did you customize iit yourself?
    Either way keep up the nice quality writing,
    it is rare to see a great blog like this one today.


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