Enumerable.Contains(Of TSource) Method (IEnumerable(Of TSource), TSource, IEqualityComparer(Of TSource))
Determines whether a sequence contains a specified element by using a specified IEqualityComparer(Of T).
Assembly: System.Core (in System.Core.dll)
'Declaration <ExtensionAttribute> _ Public Shared Function Contains(Of TSource) ( _ source As IEnumerable(Of TSource), _ value As TSource, _ comparer As IEqualityComparer(Of TSource) _ ) As Boolean
Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
- Type: System.Collections.Generic.IEnumerable(Of TSource)
A sequence in which to locate a value.
- value
- Type: TSource
The value to locate in the sequence.
- comparer
- Type: System.Collections.Generic.IEqualityComparer(Of TSource)
An equality comparer to compare values.
Return Value
Type: System.Booleantrue 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).| Exception | Condition |
|---|---|
| ArgumentNullException | 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 Property Name As String Public Property 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 hash code for the Name field if it is not null. Dim hashProductName = If(product.Name Is Nothing, 0, product.Name.GetHashCode()) ' Get 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 SP1 or later, Windows XP SP3, 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.