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IDictionary(TKey, TValue).ContainsKey Method

Determines whether the IDictionary(TKey, TValue) contains an element with the specified key.

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

abstract ContainsKey : 
        key:'TKey -> bool 

Parameters

key
Type: TKey
The key to locate in the IDictionary(TKey, TValue).

Return Value

Type: System.Boolean
true if the IDictionary(TKey, TValue) contains an element with the key; otherwise, false.

ExceptionCondition
ArgumentNullException

key is a null reference (Nothing in Visual Basic).

Implementations can vary in how they determine equality of objects; for example, the List(T) class uses Comparer(T).Default, whereas the Dictionary(TKey, TValue) class allows the user to specify the IComparer(T) implementation to use for comparing keys.

Implementations can vary in whether they allow key to be a null reference (Nothing in Visual Basic).

The following code example shows how to use the ContainsKey method to test whether a key exists prior to calling the Add method. It also shows how to use the TryGetValue method, which can be a more efficient way to retrieve values if a program frequently tries key values that are not in the dictionary. Finally, it shows how to insert items using Item property (the indexer in C#).

This code is part of a larger example that can be compiled and executed. See System.Collections.Generic.IDictionary(TKey, TValue).

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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