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Dictionary<TKey, TValue> Constructor (IDictionary<TKey, TValue>)

Initializes a new instance of the Dictionary<TKey, TValue> class that contains elements copied from the specified IDictionary<TKey, TValue> and uses the default equality comparer for the key type.

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

public Dictionary(
	IDictionary<TKey, TValue> dictionary


Type: System.Collections.Generic.IDictionary<TKey, TValue>

The IDictionary<TKey, TValue> whose elements are copied to the new Dictionary<TKey, TValue>.


dictionary is null.


dictionary contains one or more duplicate keys.

Every key in a Dictionary<TKey, TValue> must be unique according to the default equality comparer; likewise, every key in the source dictionary must also be unique according to the default equality comparer.

The initial capacity of the new Dictionary<TKey, TValue> is large enough to contain all the elements in dictionary.

Dictionary<TKey, TValue> requires an equality implementation to determine whether keys are equal. This constructor uses the default generic equality comparer, EqualityComparer<T>.Default. If type TKey implements the System.IEquatable<T> generic interface, the default equality comparer uses that implementation. Alternatively, you can specify an implementation of the IEqualityComparer<T> generic interface by using a constructor that accepts a comparer parameter.

This constructor is an O(n) operation, where n is the number of elements in dictionary.

The following code example shows how to use the Dictionary<TKey, TValue>(IEqualityComparer<TKey>) constructor to initialize a Dictionary<TKey, TValue> with sorted content from another dictionary. The code example creates a SortedDictionary<TKey, TValue> and populates it with data in random order, then passes the SortedDictionary<TKey, TValue> to the Dictionary<TKey, TValue>(IEqualityComparer<TKey>) constructor, creating a Dictionary<TKey, TValue> that is sorted. This is useful if you need to build a sorted dictionary that at some point becomes static; copying the data from a SortedDictionary<TKey, TValue> to a Dictionary<TKey, TValue> improves retrieval speed.

using System;
using System.Collections.Generic;

public class Example
    public static void Main()
        // Create a new sorted dictionary of strings, with string  
        // keys.
        SortedDictionary<string, string> openWith = 
            new SortedDictionary<string, string>();

        // Add some elements to the dictionary. 
        openWith.Add("txt", "notepad.exe");
        openWith.Add("bmp", "paint.exe");
        openWith.Add("dib", "paint.exe");
        openWith.Add("rtf", "wordpad.exe");

        // Create a Dictionary of strings with string keys, and  
        // initialize it with the contents of the sorted dictionary.
        Dictionary<string, string> copy = 
            new Dictionary<string, string>(openWith);

        // List the contents of the copy.
        foreach( KeyValuePair<string, string> kvp in copy )
            Console.WriteLine("Key = {0}, Value = {1}", 
               kvp.Key, kvp.Value);

/* This code example produces the following output:

Key = bmp, Value = paint.exe
Key = dib, Value = paint.exe
Key = rtf, Value = wordpad.exe
Key = txt, Value = notepad.exe

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0