ReadOnlyCollection(Of T) Constructor (IList(Of T))
Initializes a new instance of the ReadOnlyCollection(Of T) class that is a read-only wrapper around the specified list.
Assembly: mscorlib (in mscorlib.dll)
| Exception | Condition |
|---|---|
| ArgumentNullException | list is null. |
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" '""
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1