Returns a read-only IListT wrapper for the current collection.
Assembly: mscorlib (in mscorlib.dll)
Public Function AsReadOnly As [%$TOPIC/e78dcd75_en-us_VS_110_2_0_0_0_0%](Of T)public [%$TOPIC/e78dcd75_en-us_VS_110_2_0_1_0_0%]<T> AsReadOnly()public:
[%$TOPIC/e78dcd75_en-us_VS_110_2_0_2_0_0%]<T>^ AsReadOnly()member AsReadOnly : unit -> [%$TOPIC/e78dcd75_en-us_VS_110_2_0_3_0_0%]<'T> Return Value
Type: System.Collections.ObjectModelReadOnlyCollection TA ReadOnlyCollectionT that acts as a read-only wrapper around the current ListT.
To prevent any modifications to ListT, expose ListT only through this wrapper.
A collection that is read-only is simply a collection with a wrapper that prevents modifying the collection; therefore, if changes are made to the underlying collection, the read-only collection reflects those changes.
This method is an O(1) operation.
The following code example demonstrates the AsReadOnly method. A ListT of strings with a capacity of 4 is created, because the ultimate size of the list is known to be exactly 4. The list is populated with four strings, and the AsReadOnly method is used to get a read-only IListT generic interface implementation that wraps the original list.
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.
Imports System
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
'Deinonychususing 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
*/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
*/Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
