Contains(TSource) Method (IEnumerable(TSource), TSource, IEqualityComparer(TSource))

Enumerable.Contains<TSource> Method (IEnumerable<TSource>, TSource, IEqualityComparer<TSource>)

Updated: October 2008

Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>.

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

public static bool Contains<TSource>(
	this IEnumerable<TSource> source,
	TSource value,
	IEqualityComparer<TSource> comparer

Type Parameters


The type of the elements of source.


Type: System.Collections.Generic.IEnumerable<TSource>

A sequence in which to locate a value.

Type: TSource

The value to locate in the sequence.

Type: System.Collections.Generic.IEqualityComparer<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<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 null.

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

If comparer is null, 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 string Name { get; set; }
    public int Code { get; set; }

// Custom comparer for the Product class. 
class ProductComparer : IEqualityComparer<Product>
    // Products are equal if their names and product numbers are equal. 
    public bool Equals(Product x, Product y)

        // Check whether the compared objects reference the same data. 
        if (Object.ReferenceEquals(x, y)) return true;

        // Check whether any of the compared objects is null. 
        if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
            return false;

        // Check whether the products' properties are equal. 
        return x.Code == y.Code && x.Name == y.Name;

    // If Equals() returns true for a pair of objects, 
    // GetHashCode must return the same value for these objects. 

    public int GetHashCode(Product product)
        // Check whether the object is null. 
        if (Object.ReferenceEquals(product, null)) return 0;

        // Get the hash code for the Name field if it is not null. 
        int hashProductName = product.Name == null ? 0 : product.Name.GetHashCode();

        // Get the hash code for the Code field. 
        int hashProductCode = product.Code.GetHashCode();

        // Calculate the hash code for the product. 
        return hashProductName ^ hashProductCode;


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

Product[] fruits = { new Product { Name = "apple", Code = 9 }, 
                       new Product { Name = "orange", Code = 4 }, 
                       new Product { Name = "lemon", Code = 12 } };

Product apple = new Product { Name = "apple", Code = 9 };
Product kiwi = new Product {Name = "kiwi", Code = 8 };

ProductComparer prodc = new ProductComparer();

bool hasApple = fruits.Contains(apple, prodc);
bool 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.

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