List<T>.AsReadOnly Metodo

Definizione

Restituisce un wrapper ReadOnlyCollection<T> di sola lettura per la raccolta corrente.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)

Restituisce

ReadOnlyCollection<T>

Oggetto che fa da wrapper di sola lettura per l'oggetto List<T> corrente.An object that acts as a read-only wrapper around the current List<T>.

Esempio

Nell'esempio seguente viene illustrato il AsReadOnly metodo.The following example demonstrates the AsReadOnly method. List<T>Viene creata una delle stringhe con una capacità di 4, perché la dimensione finale dell'elenco è nota esattamente come 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. L'elenco viene popolato con quattro stringhe e il AsReadOnly metodo viene usato per ottenere un' IList<T> implementazione di interfaccia generica di sola lettura che esegue il wrapping dell'elenco originale.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 elemento dell'elenco originale è impostato su "Coelophysis" usando la Item[] Proprietà (l'indicizzatore in C#) e il contenuto dell'elenco di sola lettura viene visualizzato di nuovo per dimostrare che si tratta semplicemente di un wrapper per l'elenco originale.An element of the original list is set to "Coelophysis" using the Item[] 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

Commenti

Per evitare qualsiasi modifica all' List<T> oggetto, esporlo solo tramite questo wrapper.To prevent any modifications to the List<T> object, expose it only through this wrapper. Un ReadOnlyCollection<T> oggetto non espone metodi per la modifica della raccolta.A ReadOnlyCollection<T> object does not expose methods that modify the collection. Tuttavia, se vengono apportate modifiche all' List<T> oggetto sottostante, la raccolta di sola lettura riflette tali modifiche.However, if changes are made to the underlying List<T> object, the read-only collection reflects those changes.

Questo metodo è un'operazione O (1).This method is an O(1) operation.

Si applica a