CODEWITHSUNDEEP
c#.netdictionary
Birdman
Birdman

Reputation: 5414

Understanding the TKey and TValue parameters in the Dictionary class

I've searched a bit, but I can't seem to find any information on the TKey and TValue parameters of the Dictionary class..

  1. Is TKey just a value you specify to make a TValue unique?

  2. Is TValue just a value of your own decision that doesn't have any impact on the search of the Dictionary class?

Upvotes: 3

Views: 304

Answers (6)

David Heffernan
David Heffernan

Reputation: 612993

A dictionary is also known as an associative array, or a map.

It is a generic container just like List(T) and it contains items of type TValue. You can thus use the generic type TValue to determine the type of each element.

The key is what you use to index each item. The difference between a dictionary and a list or array is that the index for a dictionary is not restricted to being an integer. It also does not need to be contiguous. Thus the type you specify for TKey does not need to be an integer. Very often string is used.

This allows you to write something like:

Dictionary<string, int> Reputation = new Dictionary<string, int>();
Reputation["Jon Skeet"] = 360737;//and counting

If you then need to retrieve this value you can write:

int rep = Reputation["Jon Skeet"];//rep now contains the value 360737

If someone upvotes then you can write:

Reputation["Jon Skeet"] += 10;

and so on.

Upvotes: 0

clearpath
clearpath

Reputation: 956

Did you try here http://msdn.microsoft.com/en-us/library/xfhwa508.aspx

Scroll down to remarks.

Upvotes: 1

Fischermaen
Fischermaen

Reputation: 12458

A dictionary stores a Key-Value-Pair. You can take anything for to be the value and the key. You decide it, when you create such a dictionary. E.g.:

Dictionary<int, string> myDictionary = new Dictionary<int, string>();

With that you get a dictionary taking a string for to be a value and an integer for its key. It depends on what you need!

Upvotes: 0

Bernhard Hofmann
Bernhard Hofmann

Reputation: 10411

You're correct on both counts. The key is a unique value of the type you specify when you create a dictionary, and the value is any valid value for the value type you define when you create the dictionary.

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1500785

A dictionary is a mapping of keys to values.

TKey is the type of the key. TValue is the type of the value.

So for example, if I were mapping string to Person (because I had a collection of people and I wished to be able to find one by name quickly) I'd use a 

Dictionary<string, Person>

Note that the key doesn't make the value unique. There can be two keys which use the same value. However, each key is only associated with one value.

Upvotes: 4

Mitch Wheat
Mitch Wheat

Reputation: 300559

  1. Yes

  2. Yes.

Parameters prefixed with 'T' are just placeholders for a Type.

Upvotes: 0

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