CollectionBase.GetEnumerator Método
Definición
Importante
Parte de la información hace referencia a la versión preliminar del producto, que puede haberse modificado sustancialmente antes de lanzar la versión definitiva. Microsoft no otorga ninguna garantía, explícita o implícita, con respecto a la información proporcionada aquí.
Devuelve un enumerador que recorre en iteración la instancia de CollectionBase.
public:
virtual System::Collections::IEnumerator ^ GetEnumerator();public System.Collections.IEnumerator GetEnumerator ();abstract member GetEnumerator : unit -> System.Collections.IEnumerator
override this.GetEnumerator : unit -> System.Collections.IEnumeratorPublic Function GetEnumerator () As IEnumeratorDevoluciones
IEnumerator correspondiente a la instancia de CollectionBase.
Implementaciones
Ejemplos
En el ejemplo de código siguiente se implementa la CollectionBase clase y se usa esa implementación para crear una colección de Int16 objetos .
#using <System.dll>
using namespace System;
using namespace System::Collections;
public ref class Int16Collection: public CollectionBase
{
public:
property Int16 Item [int]
{
Int16 get( int index )
{
return ( (Int16)(List[ index ]));
}
void set( int index, Int16 value )
{
List[ index ] = value;
}
}
int Add( Int16 value )
{
return (List->Add( value ));
}
int IndexOf( Int16 value )
{
return (List->IndexOf( value ));
}
void Insert( int index, Int16 value )
{
List->Insert( index, value );
}
void Remove( Int16 value )
{
List->Remove( value );
}
bool Contains( Int16 value )
{
// If value is not of type Int16, this will return false.
return (List->Contains( value ));
}
protected:
virtual void OnInsert( int /*index*/, Object^ /*value*/ ) override
{
// Insert additional code to be run only when inserting values.
}
virtual void OnRemove( int /*index*/, Object^ /*value*/ ) override
{
// Insert additional code to be run only when removing values.
}
virtual void OnSet( int /*index*/, Object^ /*oldValue*/, Object^ /*newValue*/ ) override
{
// Insert additional code to be run only when setting values.
}
virtual void OnValidate( Object^ value ) override
{
if ( value->GetType() != Type::GetType( "System.Int16" ) )
throw gcnew ArgumentException( "value must be of type Int16.","value" );
}
};
void PrintIndexAndValues( Int16Collection^ myCol );
void PrintValues2( Int16Collection^ myCol );
int main()
{
// Create and initialize a new CollectionBase.
Int16Collection^ myI16 = gcnew Int16Collection;
// Add elements to the collection.
myI16->Add( (Int16)1 );
myI16->Add( (Int16)2 );
myI16->Add( (Int16)3 );
myI16->Add( (Int16)5 );
myI16->Add( (Int16)7 );
// Display the contents of the collection using the enumerator.
Console::WriteLine( "Contents of the collection (using enumerator):" );
PrintValues2( myI16 );
// Display the contents of the collection using the Count property and the Item property.
Console::WriteLine( "Initial contents of the collection (using Count and Item):" );
PrintIndexAndValues( myI16 );
// Search the collection with Contains and IndexOf.
Console::WriteLine( "Contains 3: {0}", myI16->Contains( 3 ) );
Console::WriteLine( "2 is at index {0}.", myI16->IndexOf( 2 ) );
Console::WriteLine();
// Insert an element into the collection at index 3.
myI16->Insert( 3, (Int16)13 );
Console::WriteLine( "Contents of the collection after inserting at index 3:" );
PrintIndexAndValues( myI16 );
// Get and set an element using the index.
myI16->Item[ 4 ] = 123;
Console::WriteLine( "Contents of the collection after setting the element at index 4 to 123:" );
PrintIndexAndValues( myI16 );
// Remove an element from the collection.
myI16->Remove( (Int16)2 );
// Display the contents of the collection using the Count property and the Item property.
Console::WriteLine( "Contents of the collection after removing the element 2:" );
PrintIndexAndValues( myI16 );
}
// Uses the Count property and the Item property.
void PrintIndexAndValues( Int16Collection^ myCol )
{
for ( int i = 0; i < myCol->Count; i++ )
Console::WriteLine( " [{0}]: {1}", i, myCol->Item[ i ] );
Console::WriteLine();
}
// Uses the enumerator.
void PrintValues2( Int16Collection^ myCol )
{
System::Collections::IEnumerator^ myEnumerator = myCol->GetEnumerator();
while ( myEnumerator->MoveNext() )
Console::WriteLine( " {0}", myEnumerator->Current );
Console::WriteLine();
}
/*
This code produces the following output.
Contents of the collection (using enumerator):
1
2
3
5
7
Initial contents of the collection (using Count and Item):
[0]: 1
[1]: 2
[2]: 3
[3]: 5
[4]: 7
Contains 3: True
2 is at index 1.
Contents of the collection after inserting at index 3:
[0]: 1
[1]: 2
[2]: 3
[3]: 13
[4]: 5
[5]: 7
Contents of the collection after setting the element at index 4 to 123:
[0]: 1
[1]: 2
[2]: 3
[3]: 13
[4]: 123
[5]: 7
Contents of the collection after removing the element 2:
[0]: 1
[1]: 3
[2]: 13
[3]: 123
[4]: 7
*/
using System;
using System.Collections;
public class Int16Collection : CollectionBase {
public Int16 this[ int index ] {
get {
return( (Int16) List[index] );
}
set {
List[index] = value;
}
}
public int Add( Int16 value ) {
return( List.Add( value ) );
}
public int IndexOf( Int16 value ) {
return( List.IndexOf( value ) );
}
public void Insert( int index, Int16 value ) {
List.Insert( index, value );
}
public void Remove( Int16 value ) {
List.Remove( value );
}
public bool Contains( Int16 value ) {
// If value is not of type Int16, this will return false.
return( List.Contains( value ) );
}
protected override void OnInsert( int index, Object value ) {
// Insert additional code to be run only when inserting values.
}
protected override void OnRemove( int index, Object value ) {
// Insert additional code to be run only when removing values.
}
protected override void OnSet( int index, Object oldValue, Object newValue ) {
// Insert additional code to be run only when setting values.
}
protected override void OnValidate( Object value ) {
if ( value.GetType() != typeof(System.Int16) )
throw new ArgumentException( "value must be of type Int16.", "value" );
}
}
public class SamplesCollectionBase {
public static void Main() {
// Create and initialize a new CollectionBase.
Int16Collection myI16 = new Int16Collection();
// Add elements to the collection.
myI16.Add( (Int16) 1 );
myI16.Add( (Int16) 2 );
myI16.Add( (Int16) 3 );
myI16.Add( (Int16) 5 );
myI16.Add( (Int16) 7 );
// Display the contents of the collection using foreach. This is the preferred method.
Console.WriteLine( "Contents of the collection (using foreach):" );
PrintValues1( myI16 );
// Display the contents of the collection using the enumerator.
Console.WriteLine( "Contents of the collection (using enumerator):" );
PrintValues2( myI16 );
// Display the contents of the collection using the Count property and the Item property.
Console.WriteLine( "Initial contents of the collection (using Count and Item):" );
PrintIndexAndValues( myI16 );
// Search the collection with Contains and IndexOf.
Console.WriteLine( "Contains 3: {0}", myI16.Contains( 3 ) );
Console.WriteLine( "2 is at index {0}.", myI16.IndexOf( 2 ) );
Console.WriteLine();
// Insert an element into the collection at index 3.
myI16.Insert( 3, (Int16) 13 );
Console.WriteLine( "Contents of the collection after inserting at index 3:" );
PrintIndexAndValues( myI16 );
// Get and set an element using the index.
myI16[4] = 123;
Console.WriteLine( "Contents of the collection after setting the element at index 4 to 123:" );
PrintIndexAndValues( myI16 );
// Remove an element from the collection.
myI16.Remove( (Int16) 2 );
// Display the contents of the collection using the Count property and the Item property.
Console.WriteLine( "Contents of the collection after removing the element 2:" );
PrintIndexAndValues( myI16 );
}
// Uses the Count property and the Item property.
public static void PrintIndexAndValues( Int16Collection myCol ) {
for ( int i = 0; i < myCol.Count; i++ )
Console.WriteLine( " [{0}]: {1}", i, myCol[i] );
Console.WriteLine();
}
// Uses the foreach statement which hides the complexity of the enumerator.
// NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
public static void PrintValues1( Int16Collection myCol ) {
foreach ( Int16 i16 in myCol )
Console.WriteLine( " {0}", i16 );
Console.WriteLine();
}
// Uses the enumerator.
// NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
public static void PrintValues2( Int16Collection myCol ) {
System.Collections.IEnumerator myEnumerator = myCol.GetEnumerator();
while ( myEnumerator.MoveNext() )
Console.WriteLine( " {0}", myEnumerator.Current );
Console.WriteLine();
}
}
/*
This code produces the following output.
Contents of the collection (using foreach):
1
2
3
5
7
Contents of the collection (using enumerator):
1
2
3
5
7
Initial contents of the collection (using Count and Item):
[0]: 1
[1]: 2
[2]: 3
[3]: 5
[4]: 7
Contains 3: True
2 is at index 1.
Contents of the collection after inserting at index 3:
[0]: 1
[1]: 2
[2]: 3
[3]: 13
[4]: 5
[5]: 7
Contents of the collection after setting the element at index 4 to 123:
[0]: 1
[1]: 2
[2]: 3
[3]: 13
[4]: 123
[5]: 7
Contents of the collection after removing the element 2:
[0]: 1
[1]: 3
[2]: 13
[3]: 123
[4]: 7
*/
Imports System.Collections
Public Class Int16Collection
Inherits CollectionBase
Default Public Property Item(index As Integer) As Int16
Get
Return CType(List(index), Int16)
End Get
Set
List(index) = value
End Set
End Property
Public Function Add(value As Int16) As Integer
Return List.Add(value)
End Function 'Add
Public Function IndexOf(value As Int16) As Integer
Return List.IndexOf(value)
End Function 'IndexOf
Public Sub Insert(index As Integer, value As Int16)
List.Insert(index, value)
End Sub
Public Sub Remove(value As Int16)
List.Remove(value)
End Sub
Public Function Contains(value As Int16) As Boolean
' If value is not of type Int16, this will return false.
Return List.Contains(value)
End Function 'Contains
Protected Overrides Sub OnInsert(index As Integer, value As Object)
' Insert additional code to be run only when inserting values.
End Sub
Protected Overrides Sub OnRemove(index As Integer, value As Object)
' Insert additional code to be run only when removing values.
End Sub
Protected Overrides Sub OnSet(index As Integer, oldValue As Object, newValue As Object)
' Insert additional code to be run only when setting values.
End Sub
Protected Overrides Sub OnValidate(value As Object)
If Not GetType(System.Int16).IsAssignableFrom(value.GetType()) Then
Throw New ArgumentException("value must be of type Int16.", "value")
End If
End Sub
End Class
Public Class SamplesCollectionBase
Public Shared Sub Main()
' Creates and initializes a new CollectionBase.
Dim myI16 As New Int16Collection()
' Adds elements to the collection.
myI16.Add( 1 )
myI16.Add( 2 )
myI16.Add( 3 )
myI16.Add( 5 )
myI16.Add( 7 )
' Display the contents of the collection using For Each. This is the preferred method.
Console.WriteLine("Contents of the collection (using For Each):")
PrintValues1(myI16)
' Display the contents of the collection using the enumerator.
Console.WriteLine("Contents of the collection (using enumerator):")
PrintValues2(myI16)
' Display the contents of the collection using the Count property and the Item property.
Console.WriteLine("Initial contents of the collection (using Count and Item):")
PrintIndexAndValues(myI16)
' Searches the collection with Contains and IndexOf.
Console.WriteLine("Contains 3: {0}", myI16.Contains(3))
Console.WriteLine("2 is at index {0}.", myI16.IndexOf(2))
Console.WriteLine()
' Inserts an element into the collection at index 3.
myI16.Insert(3, 13)
Console.WriteLine("Contents of the collection after inserting at index 3:")
PrintIndexAndValues(myI16)
' Gets and sets an element using the index.
myI16(4) = 123
Console.WriteLine("Contents of the collection after setting the element at index 4 to 123:")
PrintIndexAndValues(myI16)
' Removes an element from the collection.
myI16.Remove(2)
' Display the contents of the collection using the Count property and the Item property.
Console.WriteLine("Contents of the collection after removing the element 2:")
PrintIndexAndValues(myI16)
End Sub
' Uses the Count property and the Item property.
Public Shared Sub PrintIndexAndValues(myCol As Int16Collection)
Dim i As Integer
For i = 0 To myCol.Count - 1
Console.WriteLine(" [{0}]: {1}", i, myCol(i))
Next i
Console.WriteLine()
End Sub
' Uses the For Each statement which hides the complexity of the enumerator.
' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection.
Public Shared Sub PrintValues1(myCol As Int16Collection)
Dim i16 As Int16
For Each i16 In myCol
Console.WriteLine(" {0}", i16)
Next i16
Console.WriteLine()
End Sub
' Uses the enumerator.
' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection.
Public Shared Sub PrintValues2(myCol As Int16Collection)
Dim myEnumerator As System.Collections.IEnumerator = myCol.GetEnumerator()
While myEnumerator.MoveNext()
Console.WriteLine(" {0}", myEnumerator.Current)
End While
Console.WriteLine()
End Sub
End Class
'This code produces the following output.
'
'Contents of the collection (using For Each):
' 1
' 2
' 3
' 5
' 7
'
'Contents of the collection (using enumerator):
' 1
' 2
' 3
' 5
' 7
'
'Initial contents of the collection (using Count and Item):
' [0]: 1
' [1]: 2
' [2]: 3
' [3]: 5
' [4]: 7
'
'Contains 3: True
'2 is at index 1.
'
'Contents of the collection after inserting at index 3:
' [0]: 1
' [1]: 2
' [2]: 3
' [3]: 13
' [4]: 5
' [5]: 7
'
'Contents of the collection after setting the element at index 4 to 123:
' [0]: 1
' [1]: 2
' [2]: 3
' [3]: 13
' [4]: 123
' [5]: 7
'
'Contents of the collection after removing the element 2:
' [0]: 1
' [1]: 3
' [2]: 13
' [3]: 123
' [4]: 7
Comentarios
La instrucción foreach del lenguaje C# (for each en Visual Basic) oculta la complejidad de los enumeradores. Por lo tanto, se recomienda el uso de foreach, en lugar de manipular directamente el enumerador.
Los enumeradores pueden usarse para leer los datos de la colección, pero no para modificar la colección subyacente.
En principio, el enumerador se coloca antes del primer elemento de la colección. Reset también devuelve el enumerador a esta posición. En esta posición, la llamada Current produce una excepción. Por lo tanto, debe llamar a MoveNext para adelantar el enumerador hasta el primer elemento de la colección antes de leer el valor de Current.
Current devuelve el mismo objeto hasta que se llama a MoveNext o a Reset. MoveNext establece Current en el siguiente elemento.
Si MoveNext pasa el final de la colección, el enumerador se coloca después del último elemento de la colección y MoveNext devuelve false. Cuando el enumerador está en esta posición, las llamadas posteriores también devuelven MoveNext false. Si se devuelve falsela última llamada a MoveNext , la llamada Current produce una excepción. Para volver a establecer el valor de Current en el primer elemento de la colección, se puede llamar primero a Reset y después a MoveNext.
Un enumerador sigue siendo válido mientras la colección permanezca inalterada. Si se realizan cambios en la colección, como agregar, modificar o eliminar elementos, el enumerador se invalida irrecuperablemente y la siguiente llamada a MoveNext o Reset inicia una InvalidOperationExceptionexcepción . Si la colección se modifica entre MoveNext y Current, Current devuelve el elemento en el que se establece, incluso si el enumerador ya está invalidado.
La enumeración en una colección no es un procedimiento seguro para subprocesos ya que el enumerador carece de acceso exclusivo. Incluso cuando una colección está sincronizada, otros subprocesos todavía pueden modificarla, lo que hace que el enumerador produzca una excepción. Con el fin de garantizar la seguridad para la ejecución de subprocesos durante la enumeración, se puede bloquear la colección durante toda la enumeración o detectar las excepciones resultantes de los cambios realizados por otros subprocesos.
Aunque el GetEnumerator método no es visible para los clientes COM de forma predeterminada, heredar la CollectionBase clase puede exponerlo y puede provocar un comportamiento no deseado en los clientes COM.
Este método es una O(1) operación.