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ReadOnlyCollection(Of T) Constructor

Initializes a new instance of the ReadOnlyCollection(Of T) class that is a read-only wrapper around the specified list.

Namespace:  System.Collections.ObjectModel
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Sub New ( _
	list As IList(Of T) _
)

Parameters

list
Type: System.Collections.Generic.IList(Of T)

The list to wrap.

ExceptionCondition
ArgumentNullException

list is Nothing.

To prevent any modifications to list, expose list 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 constructor is an O(1) operation.

The following code example demonstrates this constructor and several members of the ReadOnlyCollection(Of T) class.

The code example creates a List(Of T) of strings and adds four dinosaur names to it. The code example then wraps the list in a ReadOnlyCollection(Of T) by passing it to the constructor.

After demonstrating the Count, Contains, Item, and IList.IndexOf members, the code example shows that the ReadOnlyCollection(Of T) is just a wrapper for the original List(Of T) by adding a new item to the List(Of T) and displaying the contents of the ReadOnlyCollection(Of T).

Finally, the code example creates an array larger than the collection and uses the CopyTo method to insert the elements of the collection into the middle of the array.

Imports System
Imports System.Collections.Generic
Imports System.Collections.ObjectModel

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs As New List(Of String)

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

        Dim readOnlyDinosaurs As _
            New ReadOnlyCollection(Of String)(dinosaurs)

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

        Console.WriteLine(vbLf & "Count: {0}", _
            readOnlyDinosaurs.Count)

        Console.WriteLine(vbLf & "Contains(""Deinonychus""): {0}", _
            readOnlyDinosaurs.Contains("Deinonychus"))

        Console.WriteLine(vbLf & _
            "readOnlyDinosaurs(3): {0}", readOnlyDinosaurs(3))

        Console.WriteLine(vbLf & "IndexOf(""Compsognathus""): {0}", _
            readOnlyDinosaurs.IndexOf("Compsognathus"))

        Console.WriteLine(vbLf & "Insert into the wrapped List:")
        Console.WriteLine("Insert(2, ""Oviraptor"")")
        dinosaurs.Insert(2, "Oviraptor")

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

        Dim dinoArray(readOnlyDinosaurs.Count + 1) As String
        readOnlyDinosaurs.CopyTo(dinoArray, 1)

        Console.WriteLine(vbLf & "Copied array has {0} elements:", _
            dinoArray.Length)
        For Each dinosaur As String In dinoArray
            Console.WriteLine("""{0}""", dinosaur)
        Next 

   End Sub 
End Class 

' This code example produces the following output: 

'Tyrannosaurus 
'Amargasaurus 
'Deinonychus 
'Compsognathus 

'Count: 4 

'Contains("Deinonychus"): True 

'readOnlyDinosaurs(3): Compsognathus 

'IndexOf("Compsognathus"): 3 

'Insert into the wrapped List: 
'Insert(2, "Oviraptor") 

'Tyrannosaurus 
'Amargasaurus 
'Oviraptor 
'Deinonychus 
'Compsognathus 

'Copied array has 7 elements: 
'"" 
'"Tyrannosaurus" 
'"Amargasaurus" 
'"Oviraptor" 
'"Deinonychus" 
'"Compsognathus" 
'""

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, 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.

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