ReadOnlyCollection(Of T).Item Property
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Gets the element at the specified index.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- index
- Type: System.Int32
The zero-based index of the element to get.
Implements
IReadOnlyList(Of T).Item(Int32)| Exception | Condition |
|---|---|
| ArgumentOutOfRangeException | index is less than zero. -or- index is equal to or greater than Count. |
This property provides the ability to access a specific element in the collection by using the following C# syntax: myCollection[index] (myCollection(index) in Visual Basic).
The C# language uses the this keyword to define the indexers instead of implementing the Item property. Visual Basic implements Item as a default property, which provides the same indexing functionality.
Retrieving the value of this property is an O(1) operation.
The following code example demonstrates 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).
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" '""