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Enumerable.Contains(Of TSource) Method (IEnumerable(Of TSource), TSource, IEqualityComparer(Of TSource))

Updated: October 2008

Determines whether a sequence contains a specified element by using a specified IEqualityComparer(Of T).

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)

<ExtensionAttribute> _
Public Shared Function Contains(Of TSource) ( _
	source As IEnumerable(Of TSource), _
	value As TSource, _
	comparer As IEqualityComparer(Of TSource) _
) As Boolean
Dim source As IEnumerable(Of TSource)
Dim value As TSource
Dim comparer As IEqualityComparer(Of TSource)
Dim returnValue As Boolean 

returnValue = source.Contains(value, _

Type Parameters


The type of the elements of source.


Type: System.Collections.Generic.IEnumerable(Of TSource)

A sequence in which to locate a value.

Type: TSource

The value to locate in the sequence.

Type: System.Collections.Generic.IEqualityComparer(Of TSource)

An equality comparer to compare values.

Return Value

Type: System.Boolean
true if the source sequence contains an element that has the specified value; otherwise, false.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable(Of TSource). When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).


source is Nothing.

Enumeration is terminated as soon as a matching element is found.

If comparer is Nothing, the default equality comparer, Default, is used to compare elements to the specified value.

The following example shows how to implement an equality comparer that can be used in the Contains method.

Public Class Product
    Public Name As String 
    Public Code As Integer 
End Class 

' Custom comparer for the Product class. 
Public Class ProductComparer
    Implements IEqualityComparer(Of Product)

    Public Function Equals1(ByVal x As Product, ByVal y As Product) As Boolean _
        Implements IEqualityComparer(Of Product).Equals

        ' Check whether the compared objects reference the same data. 
        If x Is y Then Return True 

        ' Check whether any of the compared objects is null. 
        If x Is Nothing OrElse y Is Nothing Then Return False 

        ' Check whether the products' properties are equal. 
        Return (x.Code = y.Code) AndAlso (x.Name = y.Name)
    End Function 

    Public Function GetHashCode1(ByVal product As Product) As Integer _
        Implements IEqualityComparer(Of Product).GetHashCode

        ' Check whether the object is null. 
        If product Is Nothing Then Return 0

        ' Get the hash code for the Name field if it is not null. 
        Dim hashProductName = _
            If(product.Name Is Nothing, 0, product.Name.GetHashCode())

        ' Get the hash code for the Code field. 
        Dim hashProductCode = product.Code.GetHashCode()

        ' Calculate the hash code for the product. 
        Return hashProductName Xor hashProductCode
    End Function 
End Class

After you implement this comparer, you can use a sequence of Product objects in the Contains method, as shown in the following example.

Dim fruits() As Product = _
   {New Product With {.Name = "apple", .Code = 9}, _
    New Product With {.Name = "orange", .Code = 4}, _
    New Product With {.Name = "lemon", .Code = 12}}

Dim apple = New Product With {.Name = "apple", .Code = 9}
Dim kiwi = New Product With {.Name = "kiwi", .Code = 8}

Dim prodc As New ProductComparer()

Dim hasApple = fruits.Contains(apple, prodc)
Dim hasKiwi = fruits.Contains(kiwi, prodc)

Console.WriteLine("Apple? " & hasApple)
Console.WriteLine("Kiwi? " & hasKiwi)

' This code produces the following output: 

' Apple? True 
' Kiwi? False

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

Supported in: 3.5

.NET Compact Framework

Supported in: 3.5

XNA Framework

Supported in: 3.0




October 2008

Added an example.

Customer feedback.