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C# Dictionary Tutorial

In this tutorial you will learn how to use C# Dictionary class with examples

C# Dictionary, IDictionary Object

Here you learn C# Dictionary , IDictionary today, to access this object you need use the namespace System.Collections.Generic

C# Dictionary has no different meaning than English Dictionary word, it has exact same meaning, In C# Dictionary we can store information with key, value combination, and retrieve the value using the key.

Before we see some C# Dictionary Example, let’s look at some of the Important Properties

C# Dictionary Methods

  • Add

    Add key-value pairs <TKey, TValue> in Dictionary collection.

  • Add

    Adds an item with a key and value into the Dictionary.

  • TryGetValue

    Returns true and specified key assigns value in (out) parameter, if key does not exists then return false.

  • ContainsKey

    Checks whether the specified key (integer) exists in Dictionary object collection

  • Contains

    Checks whether the specified KeyValuePair exists in Dictionary<TKey, TValue>

C# Dictionary Example

Note: While adding in Dictionary object, you cannot add duplicate or null keys in C# Dictionary, though values can be duplicated or set as null, but Keys must be unique otherwise it will throw runtime exception.

using System.Collections.Generic;
            
IDictionary<int, string> _dictObj = new Dictionary<int, string>();
_dictObj.Add(1, "C# Dictionary Example");
_dictObj.Add(2, "Learning C# .Net");
_dictObj.Add(3, "Learning SQL Database");
_dictObj.Add(4, "Learning ASP.Net");
Retrieve value from C# Dictionary object Example

Two ways you can retrieve value from Dictionary object.

  • To retrieve single value from C# Dictionary object using key
    Console.WriteLine(_dictObj[1]);

    If the specified key does not exist then it will throw KeyNotFoundException.

  • To retrieve all values from Dictionary object using keys-collection
    for (int i = 0; i < _dictObj.Count; i++)
    {
        Console.WriteLine("Key: {0}  Value: {1}", _dictObj.Keys.ElementAt(i), _dictObj[_dictObj.Keys.ElementAt(i)]);
    }

TryGetValue in C# Dictionary Example

Suppose we are trying to find index 4 in above dictionary object using TryGetValue method

string _valueResult;             
if (_dictObj.TryGetValue(4, out _valueResult))
{
    Console.WriteLine(_valueResult);
}
else
{
    Console.WriteLine("Specified key not found.");
}

Contains in C# Dictionary

Contains method will check if KeyValuePair is found in collection, returns true or false

_dictObj.Contains(new KeyValuePair<int, string>(1, "C# Dictionary Example"));
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