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List<T>.Contains Method

Updated: January 2010

Determines whether an element is in the List<T>.

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

public bool Contains(
	T item


Type: T

The object to locate in the List<T>. The value can be null for reference types.

Return Value

Type: System.Boolean
true if item is found in the List<T>; otherwise, false.



This method determines equality using the default equality comparer as defined by the object's implementation of the IEquatable<T>.Equals method for T, the type of values in the list.

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

The following example contains a list of complex objects of type Box. The Box class implements the IEquatable<T>.Equals method so that two boxes are considered equal if their dimensions are the same. In this example, the Contains method returns true, because a box that has the specified dimensions is already in the collection.

using System;
using System.Collections.Generic;

class Program
    static void Main(string[] args)
        List<Box> boxes = new List<Box>();

        boxes.Add(new Box(8, 8, 4));
        boxes.Add(new Box(8, 4, 8));
        boxes.Add(new Box(8, 6, 4));

        if (boxes.Contains(new Box(8, 6, 4)))
            Console.WriteLine("An equal box is already in the collection.");
            Console.WriteLine("Box can be added.");

public class Box : IEquatable<Box>

    public Box(int h, int l, int w)
        this.Height = h;
        this.Length = l;
        this.Width = w;
    public int Height { get; set; }
    public int Length { get; set; }
    public int Width { get; set; }

    public bool Equals(Box other)
        if (this.Height == other.Height & this.Length == other.Length
            & this.Width == other.Width)
            return true;
            return false;

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, 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, 3.0, 2.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0




January 2010

Added example.

Information enhancement.