Dictionary<'TKey, 'TValue>.ContainsKey Method ('TKey)

 

Determines whether the Dictionary<'TKey, 'TValue> contains the specified key.

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

abstract ContainsKey : 
        key:'TKey -> bool
override ContainsKey : 
        key:'TKey -> bool

Parameters

key
Type: TKey

The key to locate in the Dictionary<'TKey, 'TValue>.

Return Value

Type: System.Boolean

true if the Dictionary<'TKey, 'TValue> contains an element with the specified key; otherwise, false.

Exception Condition
ArgumentNullException

key is null.

This method approaches an O(1) operation.

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 to retrieve values, which is an efficient way to retrieve values when a program frequently tries keys that are not in the dictionary. Finally, it shows the least efficient way to test whether keys exist, by using the Item property (the indexer in C#).

This code example is part of a larger example provided for the Dictionary<'TKey, 'TValue> class (openWith is the name of the Dictionary used in this example).

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

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
Return to top
Show: