ReadOnlyCollection(Of T) Constructor
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
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)
Parameters
- list
- Type: System.Collections.Generic.IList(Of T)
The list to wrap.
| Exception | Condition |
|---|---|
| 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.Collections.Generic Imports System.Collections.ObjectModel Public Class Example Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock) 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) outputBlock.Text &= vbCrLf For Each dinosaur As String In readOnlyDinosaurs outputBlock.Text &= dinosaur & vbCrLf Next outputBlock.Text &= String.Format(vbLf & "Count: {0}", _ readOnlyDinosaurs.Count) & vbCrLf outputBlock.Text &= String.Format(vbLf & "Contains(""Deinonychus"" & vbCrLf: {0}", _ readOnlyDinosaurs.Contains("Deinonychus")) outputBlock.Text &= String.Format(vbLf & _ "readOnlyDinosaurs(3): {0}", readOnlyDinosaurs(3)) & vbCrLf outputBlock.Text &= String.Format(vbLf & "IndexOf(""Compsognathus"" & vbCrLf: {0}", _ readOnlyDinosaurs.IndexOf("Compsognathus")) outputBlock.Text &= vbLf & "Insert into the wrapped List:" & vbCrLf outputBlock.Text &= String.Format("Insert(2, ""Oviraptor"")") & vbCrLf dinosaurs.Insert(2, "Oviraptor") outputBlock.Text &= vbCrLf For Each dinosaur As String In readOnlyDinosaurs outputBlock.Text &= dinosaur & vbCrLf Next Dim dinoArray(readOnlyDinosaurs.Count + 1) As String readOnlyDinosaurs.CopyTo(dinoArray, 1) outputBlock.Text &= String.Format(vbLf & "Copied array has {0} elements:", _ dinoArray.Length) & vbCrLf For Each dinosaur As String In dinoArray outputBlock.Text &= String.Format("""{0}""", dinosaur) & vbCrLf 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" '""