# List<T>.Contains(T) Método

## Definición

Determina si un elemento se encuentra en List<T>.Determines whether an element is in the List<T>.

public:
virtual bool Contains(T item);
public bool Contains (T item);
abstract member Contains : 'T -> bool
override this.Contains : 'T -> bool
Public Function Contains (item As T) As Boolean

#### Parámetros

item
T

Objeto que se va a buscar en List<T>.The object to locate in the List<T>. El valor puede ser null para los tipos de referencia.The value can be null for reference types.

#### Devoluciones

Boolean

true si item se encuentra en la matriz List<T>; en caso contrario, false.true if item is found in the List<T>; otherwise, false.

## Ejemplos

En el ejemplo siguiente se muestran los Contains Exists métodos y en List<T> que contiene un objeto comercial simple que implementa Equals .The following example demonstrates the Contains and Exists methods on a List<T> that contains a simple business object that implements Equals.

using System;
using System.Collections.Generic;
// Simple business object. A PartId is used to identify a part
// but the part name can change.
public class Part : IEquatable<Part>
{
public string PartName { get; set; }
public int PartId { get; set; }

public override string ToString()
{
return "ID: " + PartId + "   Name: " + PartName;
}
public override bool Equals(object obj)
{
if (obj == null) return false;
Part objAsPart = obj as Part;
if (objAsPart == null) return false;
else return Equals(objAsPart);
}
public override int GetHashCode()
{
return PartId;
}
public bool Equals(Part other)
{
if (other == null) return false;
return (this.PartId.Equals(other.PartId));
}
// Should also override == and != operators.
}
public class Example
{
public static void Main()
{
// Create a list of parts.
List<Part> parts = new List<Part>();

// Add parts to the list.
parts.Add(new Part() { PartName = "crank arm", PartId = 1234 });
parts.Add(new Part() { PartName = "chain ring", PartId = 1334 });
parts.Add(new Part() { PartName = "regular seat", PartId = 1434 });
parts.Add(new Part() { PartName = "banana seat", PartId = 1444 });
parts.Add(new Part() { PartName = "cassette", PartId = 1534 });
parts.Add(new Part() { PartName = "shift lever", PartId = 1634 }); ;

// Write out the parts in the list. This will call the overridden ToString method
// in the Part class.
Console.WriteLine();
foreach (Part aPart in parts)
{
Console.WriteLine(aPart);
}

// Check the list for part #1734. This calls the IEquatable.Equals method
// of the Part class, which checks the PartId for equality.
Console.WriteLine("\nContains: Part with Id=1734: {0}",
parts.Contains(new Part { PartId = 1734, PartName = "" }));

// Find items where name contains "seat".
Console.WriteLine("\nFind: Part where name contains \"seat\": {0}",
parts.Find(x => x.PartName.Contains("seat")));

// Check if an item with Id 1444 exists.
Console.WriteLine("\nExists: Part with Id=1444: {0}",
parts.Exists(x => x.PartId == 1444));

/*This code example produces the following output:

ID: 1234   Name: crank arm
ID: 1334   Name: chain ring
ID: 1434   Name: regular seat
ID: 1444   Name: banana seat
ID: 1534   Name: cassette
ID: 1634   Name: shift lever

Contains: Part with Id=1734: False

Find: Part where name contains "seat": ID: 1434   Name: regular seat

Exists: Part with Id=1444: True
*/
}
}
Imports System.Collections.Generic

' Simple business object. A PartId is used to identify a part
' but the part name can change.
Public Class Part
Implements IEquatable(Of Part)
Public Property PartName() As String
Get
Return m_PartName
End Get
Set(value As String)
m_PartName = Value
End Set
End Property
Private m_PartName As String
Public Property PartId() As Integer
Get
Return m_PartId
End Get
Set(value As Integer)
m_PartId = Value
End Set
End Property
Private m_PartId As Integer

Public Overrides Function ToString() As String
Return Convert.ToString("ID: " & PartId & "   Name: ") & PartName
End Function
Public Overrides Function Equals(obj As Object) As Boolean
If obj Is Nothing Then
Return False
End If
Dim objAsPart As Part = TryCast(obj, Part)
If objAsPart Is Nothing Then
Return False
Else
Return Equals(objAsPart)
End If
End Function
Public Overrides Function GetHashCode() As Integer
Return PartId
End Function
Public Overloads Function Equals(other As Part) As Boolean _
Implements IEquatable(Of Part).Equals
If other Is Nothing Then
Return False
End If
Return (Me.PartId.Equals(other.PartId))
End Function
' Should also override == and != operators.
End Class
Public Class Example
Public Shared Sub Main()
' Create a list of parts.
Dim parts As New List(Of Part)()

' Add parts to the list.
.PartName = "crank arm", _
.PartId = 1234 _
})
.PartName = "chain ring", _
.PartId = 1334 _
})
.PartName = "regular seat", _
.PartId = 1434 _
})
.PartName = "banana seat", _
.PartId = 1444 _
})
.PartName = "cassette", _
.PartId = 1534 _
})
.PartName = "shift lever", _
.PartId = 1634 _
})

' Write out the parts in the list. This will call the overridden ToString method
' in the Part class.
Console.WriteLine()
For Each aPart As Part In parts
Console.WriteLine(aPart)
Next

' Check the list for part #1734. This calls the IEquatable.Equals method
' of the Part class, which checks the PartId for equality.
Console.WriteLine(vbLf & "Contains: Part with Id=1734: {0}",
parts.Contains(New Part() With { _
.PartId = 1734, _
.PartName = "" _
}))

' Find items where name contains "seat".
Console.WriteLine(vbLf & "Find: Part where name contains ""seat"": {0}",
parts.Find(Function(x) x.PartName.Contains("seat")))

' Check if an item with Id 1444 exists.
Console.WriteLine(vbLf & "Exists: Part with Id=1444: {0}",
parts.Exists(Function(x) x.PartId = 1444))

'This code example produces the following output:
'
'        ID: 1234   Name: crank arm
'        ID: 1334   Name: chain ring
'        ID: 1434   Name: regular seat
'        ID: 1444   Name: banana seat
'        ID: 1534   Name: cassette
'        ID: 1634   Name: shift lever
'
'        Contains: Part with Id=1734: False
'
'        Find: Part where name contains "seat": ID: 1434   Name: regular seat
'
'        Exists: Part with Id=1444: True
'

End Sub
End Class

El ejemplo siguiente contiene una lista de objetos complejos de tipo Cube .The following example contains a list of complex objects of type Cube. La Cube clase implementa el IEquatable<T>.Equals método para que dos cubos se consideren iguales si sus dimensiones son las mismas.The Cube class implements the IEquatable<T>.Equals method so that two cubes are considered equal if their dimensions are the same. En este ejemplo, el Contains método devuelve true , porque ya hay en la colección un cubo con las dimensiones especificadas.In this example, the Contains method returns true, because a cube that has the specified dimensions is already in the collection.

using System;
using System.Collections.Generic;

class Program
{
static void Main(string[] args)
{
List<Cube> cubes = new List<Cube>();

if (cubes.Contains(new Cube(8, 6, 4))) {
Console.WriteLine("An equal cube is already in the collection.");
}
else {
}

//Outputs "An equal cube is already in the collection."
}
}

public class Cube : IEquatable<Cube>
{

public Cube(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(Cube other)
{
if (this.Height == other.Height && this.Length == other.Length
&& this.Width == other.Width) {
return true;
}
else {
return false;
}
}
}
Imports System.Collections.Generic

Class Program
Public Shared Sub Main(ByVal args As String())
Dim cubes As New List(Of Cube)()

If cubes.Contains(New Cube(8, 6, 4)) Then
Console.WriteLine("An equal cube is already in the collection.")
Else
End If

'Outputs "An equal cube is already in the collection."
End Sub
End Class

Public Class Cube
Implements IEquatable(Of Cube)

Public Sub New(ByVal h As Integer, ByVal l As Integer, ByVal w As Integer)
Me.Height = h
Me.Length = l
Me.Width = w
End Sub
Private _Height As Integer
Public Property Height() As Integer
Get
Return _Height
End Get
Set(ByVal value As Integer)
_Height = value
End Set
End Property
Private _Length As Integer
Public Property Length() As Integer
Get
Return _Length
End Get
Set(ByVal value As Integer)
_Length = value
End Set
End Property
Private _Width As Integer
Public Property Width() As Integer
Get
Return _Width
End Get
Set(ByVal value As Integer)
_Width = value
End Set
End Property

Public Overloads Function Equals(ByVal other As Cube) _
As Boolean Implements IEquatable(Of Cube).Equals
If Me.Height = other.Height And Me.Length = other.Length _
And Me.Width = other.Width Then
Return True
Else
Return False
End If
End Function
End Class

## Comentarios

Este método determina la igualdad mediante el comparador de igualdad predeterminado, tal y como se define en la implementación del objeto del IEquatable<T>.Equals método para T (el tipo de valores de la lista).This method determines equality by 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).

Este método realiza una búsqueda lineal; por lo tanto, este método es una operación O (n), donde n es Count .This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.