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


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: 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.

Type Parameters


The type of the elements of source.

Exception Condition

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

        //Get 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<TSource> 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

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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