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

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<TKeyTValue>

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

Exception Condition

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

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
Return to top
© 2015 Microsoft