NameValueCollection vs Dictionary<string,string> [duplicate]

Solution 1:

They aren't semantically identical. The NameValueCollection can have duplicate keys while the Dictionary cannot.

Personally if you don't have duplicate keys, then I would stick with the Dictionary. It's more modern, uses IEnumerable<> which makes it easy to mingle with Linq queries. You can even create a Dictionary using the Linq ToDictionary() method.

Solution 2:

NameValueCollection is string typed whereas Dictionary leverages generics to allow type variance. See Benefits of Generics.

Solution 3:

Dictionary will be much faster. NameValueCollection allows duplicate keys. Which could be bad in certain situations, or desired in other. Dictionary does not allow duplicate keys.

From: http://msdn.microsoft.com/en-us/library/xfhwa508.aspx

The Dictionary<(Of <(TKey, TValue>)>) generic class provides a mapping from a set of keys to a set of values. Each addition to the dictionary consists of a value and its associated key. Retrieving a value by using its key is very fast, close to O(1), because the Dictionary<(Of <(TKey, TValue>)>) class is implemented as a hash table.