`NameValueCollection`

With this VB.NET collection, we can store many values for a single key. All keys and values must be strings.

We can access values associated with a key, and loop over all keys with AllKeys. And we can get keys and values by index by passing an Integer argument.

Example

We import the System.Collections Specialized namespace to allow the NameValueCollection to be more easily accessed in this VB.NET program.

Part 1 We create a NameValueCollection. For the strings "cat" and "dog", we add 2 values each.

Part 2 To loop over the keys in a NameValueCollection, we access the AllKeys property in a For-Each loop.

Part 3 To get a value for an associated key, we can access the NameValueCollection directly.

Part 4 To test for an empty NameValueCollection, consider using the HasKeys property.

Part 5 We can access keys with GetKey and an index argument—the internal storage of the NameValueCollection can be accessed by index.

Part 6 Similar to GetKey, the Get() Function is a way to access values by their index.

Imports System.Collections.Specialized

Module Module1

    Sub Main()

        ' Part 1: create a NameValueCollection.
        Dim collection = New NameValueCollection()
        collection.Add("cat", "orange")
        collection.Add("dog", "brown")
        collection.Add("dog", "white")
        collection.Add("cat", "black")

        ' Part 2: use for-each over AllKeys.
        For Each key In collection.AllKeys
            Console.WriteLine(key)
        Next

        ' Part 3: access values using keys.
        Console.WriteLine(collection("cat"))
        Console.WriteLine(IsNothing(collection("x")))

        ' Part 4: call HasKeys.
        Console.WriteLine(collection.HasKeys())

        ' Part 5: call GetKey at index 0.
        Console.WriteLine(collection.GetKey(0))

        ' Part 6: call Get at index 0.
        Dim value = collection.Get(0)
        Console.WriteLine(value)

    End Sub

End Modulecat
dog
orange,black
True
True
cat
orange,black

NameValueCollection is a built-in way to associate multiple values with a single key. Its performance is not ideal, and in most VB.NET programs we are better served by Dictionary or List.