.Net 中 NameValueCollection 的通用形式

Question

Does .Net provides generic form of NameValueCollection or an alternative to Dictionary<string,List<T>> ?

Something like

Person john = new Person();
...
Person vick = new Person();
...

NameValueCollection<Person> stringToPerson = new  NameValueCollection<Person>();
stringToPerson.Add("John",john)
stringToPerson.Add("Vick",vick)

Actually in my case am forced to rely on Dictionary<string,List<Peron>> , is there any other alternative?

Regards, Jeez

Answer 1

The closest alternative is probably the ILookup<TKey, TElement> interface. At the moment, the only public type that implements it in the BCL is the immutable Lookup<TKey, TElement> class, an instance of which can be created with the Enumerable.ToLookup method. If you want a mutable type that implements the interface, you'll have to write one yourself; you can find an example implementation here .

In your case, you probably want an ILookup<string, Person> .

Answer 2

There's no such thing built in to the BCL as far as I know. I would just write your own class which wraps a Dictionary<string, List<T>> internally and exposes appropriate methods (eg, Add could add an element to the List<T> for the given key).

For example:

class NameValueCollection<T>
{
    Dictionary<string, List<T>> _dict = new Dictionary<string, List<T>>();

    public void Add(string name, T value)
    {
        List<T> list;
        if (!_dict.TryGetValue(name, out list))
        {
            _dict[name] = list = new List<T>();
        }

        list.Add(value);
    }

    // etc.
}

Answer 3

Oh, I see what you want to do now. You want to be able to add to the Person collection without having to create a new List each time. Extension methods to the rescue!

public static void SafeAdd<TValue>(this IDictionary<TKey, ICollection<TValue>> dict, TKey key, TValue value)
{
     HashSet<T> container;
     if (!dict.TryGetValue(key, out container)) 
     {
         dict[key] = new HashSet<TValue>();
     }
     dict[key].Add(value);
}

Usage:
var names = new Dictionary<string, ICollection<Person>>();
names.SafeAdd("John", new Person("John"));

Answer 4

Nothing inbuilt; there is Lookup<TKey,TValue> which operates as a multi-map, but that is immutable. I wrote a mutable EditableLookup<TKey,TValue> for MiscUtil which may help.

Answer 5

Here is a C# example of complete implementation of the generic NameValueCollection based on NameObjectCollectionBase . What makes this collection special unlike Dictionary , is that one key can contain several elements.

Usage:

NameValueCollection<int> collection = new NameValueCollection<int>();
collection.Add("a", 123);
collection.Add("a", 456); // 123 and 456 will be inserted into the same key. 
collection.Add("b", 789); // 789 will be inserted into another key.

int[] a = collection.Get("a"); // contains 132 and 456.
int[] b = collection.Get("b"); // contains 789.