List<T>.AsReadOnly Méthode

Définition

Retourne un wrapper ReadOnlyCollection<T> en lecture seule pour la collection actuelle.Returns a read-only ReadOnlyCollection<T> wrapper for the current collection.

public:
 System::Collections::ObjectModel::ReadOnlyCollection<T> ^ AsReadOnly();
public System.Collections.ObjectModel.ReadOnlyCollection<T> AsReadOnly ();
member this.AsReadOnly : unit -> System.Collections.ObjectModel.ReadOnlyCollection<'T>
Public Function AsReadOnly () As ReadOnlyCollection(Of T)

Retours

Objet qui joue le rôle de wrapper en lecture seule autour du List<T> actuel.An object that acts as a read-only wrapper around the current List<T>.

Exemples

L’exemple suivant illustre la méthode AsReadOnly.The following example demonstrates the AsReadOnly method. Une List<T> de chaînes avec une capacité de 4 est créée, car la taille ultime de la liste est connue exactement 4.A List<T> of strings with a capacity of 4 is created, because the ultimate size of the list is known to be exactly 4. La liste est remplie avec quatre chaînes, et la méthode AsReadOnly est utilisée pour obtenir une implémentation d’interface générique IList<T> en lecture seule qui encapsule la liste d’origine.The list is populated with four strings, and the AsReadOnly method is used to get a read-only IList<T> generic interface implementation that wraps the original list.

Un élément de la liste d’origine est défini sur « Coelophysis » à l’aide de la propriété Item[Int32] ( C#l’indexeur dans) et le contenu de la liste en lecture seule s’affiche à nouveau pour démontrer qu’il s’agit simplement d’un wrapper pour la liste d’origine.An element of the original list is set to "Coelophysis" using the Item[Int32] property (the indexer in C#), and the contents of the read-only list are displayed again to demonstrate that it is just a wrapper for the original list.

using namespace System;
using namespace System::Collections::Generic;

void main()
{
    List<String^>^ dinosaurs = gcnew List<String^>(4);

    Console::WriteLine("\nCapacity: {0}", dinosaurs->Capacity);

    dinosaurs->Add("Tyrannosaurus");
    dinosaurs->Add("Amargasaurus");
    dinosaurs->Add("Mamenchisaurus");
    dinosaurs->Add("Deinonychus");

    Console::WriteLine();
    for each(String^ dinosaur in dinosaurs)
    {
        Console::WriteLine(dinosaur);
    }

    Console::WriteLine("\nIList<String^>^ roDinosaurs = dinosaurs->AsReadOnly()");
    IList<String^>^ roDinosaurs = dinosaurs->AsReadOnly();

    Console::WriteLine("\nElements in the read-only IList:");
    for each(String^ dinosaur in roDinosaurs)
    {
        Console::WriteLine(dinosaur);
    }

    Console::WriteLine("\ndinosaurs[2] = \"Coelophysis\"");
    dinosaurs[2] = "Coelophysis";

    Console::WriteLine("\nElements in the read-only IList:");
    for each(String^ dinosaur in roDinosaurs)
    {
        Console::WriteLine(dinosaur);
    }
}

/* This code example produces the following output:

Capacity: 4

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

IList<String^>^ roDinosaurs = dinosaurs->AsReadOnly()

Elements in the read-only IList:
Tyrannosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

dinosaurs[2] = "Coelophysis"

Elements in the read-only IList:
Tyrannosaurus
Amargasaurus
Coelophysis
Deinonychus
 */
using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        List<string> dinosaurs = new List<string>(4);

        Console.WriteLine("\nCapacity: {0}", dinosaurs.Capacity);

        dinosaurs.Add("Tyrannosaurus");
        dinosaurs.Add("Amargasaurus");
        dinosaurs.Add("Mamenchisaurus");
        dinosaurs.Add("Deinonychus");

        Console.WriteLine();
        foreach(string s in dinosaurs)
        {
            Console.WriteLine(s);
        }

        Console.WriteLine("\nIList<string> roDinosaurs = dinosaurs.AsReadOnly()");
        IList<string> roDinosaurs = dinosaurs.AsReadOnly();

        Console.WriteLine("\nElements in the read-only IList:");
        foreach(string dinosaur in roDinosaurs)
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\ndinosaurs[2] = \"Coelophysis\"");
        dinosaurs[2] = "Coelophysis";

        Console.WriteLine("\nElements in the read-only IList:");
        foreach(string dinosaur in roDinosaurs)
        {
            Console.WriteLine(dinosaur);
        }
    }
}

/* This code example produces the following output:

Capacity: 4

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

IList<string> roDinosaurs = dinosaurs.AsReadOnly()

Elements in the read-only IList:
Tyrannosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

dinosaurs[2] = "Coelophysis"

Elements in the read-only IList:
Tyrannosaurus
Amargasaurus
Coelophysis
Deinonychus
 */
Imports System.Collections.Generic

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs As New List(Of String)(4)

        Console.WriteLine(vbLf & "Capacity: {0}", dinosaurs.Capacity)

        dinosaurs.Add("Tyrannosaurus")
        dinosaurs.Add("Amargasaurus")
        dinosaurs.Add("Mamenchisaurus")
        dinosaurs.Add("Deinonychus")

        Console.WriteLine()
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next

        Console.WriteLine(vbLf & _
            "Dim roDinosaurs As IList(Of String) = dinosaurs.AsReadOnly")
        Dim roDinosaurs As IList(Of String) = dinosaurs.AsReadOnly

        Console.WriteLine(vbLf & "Elements in the read-only IList:")
        For Each dinosaur As String In roDinosaurs
            Console.WriteLine(dinosaur)
        Next

        Console.WriteLine(vbLf & "dinosaurs(2) = ""Coelophysis""")
        dinosaurs(2) = "Coelophysis"

        Console.WriteLine(vbLf & "Elements in the read-only IList:")
        For Each dinosaur As String In roDinosaurs
            Console.WriteLine(dinosaur)
        Next

    End Sub
End Class

' This code example produces the following output:
'
'Capacity: 4
'
'Tyrannosaurus
'Amargasaurus
'Mamenchisaurus
'Deinonychus
'
'Dim roDinosaurs As IList(Of String) = dinosaurs.AsReadOnly
'
'Elements in the read-only IList:
'Tyrannosaurus
'Amargasaurus
'Mamenchisaurus
'Deinonychus
'
'dinosaurs(2) = "Coelophysis"
'
'Elements in the read-only IList:
'Tyrannosaurus
'Amargasaurus
'Coelophysis
'Deinonychus

Remarques

Pour empêcher toute modification de l’objet List<T>, exposez-le uniquement par le biais de ce wrapper.To prevent any modifications to the List<T> object, expose it only through this wrapper. Un objet ReadOnlyCollection<T> n’expose pas les méthodes qui modifient la collection.A ReadOnlyCollection<T> object does not expose methods that modify the collection. Toutefois, si des modifications sont apportées à l’objet List<T> sous-jacent, la collection en lecture seule reflète ces modifications.However, if changes are made to the underlying List<T> object, the read-only collection reflects those changes.

Cette méthode est une opération O (1).This method is an O(1) operation.

S’applique à