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Hashtable.ContainsValue Method

Determines whether the Hashtable contains a specific value.

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

'Declaration
Public Overridable Function ContainsValue ( _
	value As Object _
) As Boolean

Parameters

value
Type: System.Object

The value to locate in the Hashtable. The value can be Nothing.

Return Value

Type: System.Boolean
true if the Hashtable contains an element with the specified value; otherwise, false.

The values of the elements of the Hashtable are compared to the specified value using the Object.Equals method.

This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

Starting with the .NET Framework 2.0, this method uses the collection’s objects’ Equals and CompareTo methods on item to determine whether item exists. In the earlier versions of the .NET Framework, this determination was made by using the Equals and CompareTo methods of the item parameter on the objects in the collection.

The following example shows how to determine whether the Hashtable contains a specific element.

Imports System
Imports System.Collections

Public Class SamplesHashtable

    Public Shared Sub Main()

        ' Creates and initializes a new Hashtable. 
        Dim myHT As New Hashtable()
        myHT.Add(0, "zero")
        myHT.Add(1, "one")
        myHT.Add(2, "two")
        myHT.Add(3, "three")
        myHT.Add(4, "four")

        ' Displays the values of the Hashtable.
        Console.WriteLine("The Hashtable contains the following values:")
        PrintIndexAndKeysAndValues(myHT)

        ' Searches for a specific key. 
        Dim myKey As Integer = 2
        Console.Write("The key ""{0}"" is ", myKey)
        If(myHT.ContainsKey(myKey))
           Console.WriteLine("in the Hashtable.")
        Else
           Console.WriteLine("NOT in the Hashtable.")
        End If

        myKey = 6
        Console.Write("The key ""{0}"" is ", myKey)
        If(myHT.ContainsKey(myKey))
           Console.WriteLine(" in the Hashtable.")
        Else
           Console.WriteLine(" NOT in the Hashtable.")
        End If 

        ' Searches for a specific value. 
        Dim myValue As String = "three"
        Console.Write("The value ""{0}"" is ", myValue)
        If(myHT.ContainsValue(myValue))
           Console.WriteLine(" in the Hashtable.")
        Else
           Console.WriteLine(" NOT in the Hashtable.")
        End If

        myValue = "nine"
        Console.Write("The value ""{0}"" is ", myValue)
        If(myHT.ContainsValue(myValue))
           Console.WriteLine(" in the Hashtable.")
        Else
           Console.WriteLine(" NOT in the Hashtable.")
        End If 

    End Sub 'Main

    Public Shared Sub PrintIndexAndKeysAndValues(myHT As Hashtable)
        Dim i As Integer = 0
        Console.WriteLine(vbTab + "-INDEX-" + vbTab + "-KEY-" + vbTab + "-VALUE-")
        Dim de As DictionaryEntry
        For Each de In  myHT
            Console.WriteLine(vbTab + "[{0}]:" + vbTab + "{1}" + vbTab + "{2}", i, de.Key, de.Value)
            i = i + 1
        Next de
        Console.WriteLine()
    End Sub 'PrintIndexAndKeysAndValues

End Class 'SamplesHashtable 


' This code produces the following output. 
'  
' The Hashtable contains the following values: 
'         -INDEX- -KEY-   -VALUE- 
'         [0]:    4       four 
'         [1]:    3       three 
'         [2]:    2       two 
'         [3]:    1       one 
'         [4]:    0       zero 

' The key "2" is in the Hashtable. 
' The key "6" is NOT in the Hashtable. 
' The value "three" is in the Hashtable. 
' The value "nine" is NOT in the Hashtable.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0
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