Dictionary(Of TKey, TValue).IDictionary.Contains Method (Object)

 

Determines whether the IDictionary contains an element with the specified key.

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

Private Function Contains (
	key As Object
) As Boolean
	Implements IDictionary.Contains

Parameters

key
Type: System.Object

The key to locate in the IDictionary.

Return Value

Type: System.Boolean

true if the IDictionary contains an element with the specified key; otherwise, false.

Exception Condition
ArgumentNullException

key is null.

This method returns false if key is of a type that is not assignable to the key type TKey of the Dictionary(Of TKey, TValue).

This method approaches an O(1) operation.

The following code example shows how to use the IDictionary.Contains method of the System.Collections.IDictionary interface with a Dictionary(Of TKey, TValue). The example demonstrates that the method returns false if a key of the wrong data type is supplied.

The code example is part of a larger example, including output, provided for the IDictionary.Add method.

Imports System
Imports System.Collections
Imports System.Collections.Generic

Public Class Example

    Public Shared Sub Main() 

        ' Create a new dictionary of strings, with string keys,
        ' and access it using the IDictionary interface.
        '
        Dim openWith As IDictionary = _
            New Dictionary(Of String, String)

        ' Add some elements to the dictionary. There are no 
        ' duplicate keys, but some of the values are duplicates.
        ' IDictionary.Add throws an exception if incorrect types
        ' are supplied for key or value.
        openWith.Add("txt", "notepad.exe")
        openWith.Add("bmp", "paint.exe")
        openWith.Add("dib", "paint.exe")
        openWith.Add("rtf", "wordpad.exe")
' Contains can be used to test keys before inserting 
' them.
If Not openWith.Contains("ht") Then
    openWith.Add("ht", "hypertrm.exe")
    Console.WriteLine("Value added for key = ""ht"": {0}", _
        openWith("ht"))
End If

' IDictionary.Contains returns False if the wrong data 
' type is supplied.
Console.WriteLine("openWith.Contains(29.7) returns {0}", _
    openWith.Contains(29.7))

    End Sub

End Class

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
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