Collection Generic Class
Assembly: mscorlib (in mscorlib.dll)
'Declaration <SerializableAttribute> _ <ComVisibleAttribute(False)> _ Public Class Collection(Of T) Implements IList(Of T), ICollection(Of T), _ IEnumerable(Of T), IList, ICollection, _ IEnumerable 'Usage Dim instance As Collection(Of T)
J# supports the use of generic types and methods, but not the declaration of new ones.
JScript does not support generic types and methods.
Not applicable.
Type Parameters
- T
The type of elements in the collection.
The Collection class can be used immediately by creating an instance of one of its constructed types; all you have to do is specify the type of object to be contained in the collection. In addition, you can derive your own collection type from any constructed type, or derive a generic collection type from the Collection class itself.
The Collection class provides protected methods that can be used to customize its behavior when adding and removing items, clearing the collection, or setting the value of an existing item.
Most Collection objects can be modified. However, a Collection object that is initialized with a read-only IList object cannot be modified. See ReadOnlyCollection for a read-only version of this class.
Elements in this collection can be accessed using an integer index. Indexes in this collection are zero-based.
Collection accepts a null reference (Nothing in Visual Basic) as a valid value for reference types and allows duplicate elements.
Notes to Implementers: This base class is provided to make it easier for implementers to create a custom collection. Implementers are encouraged to extend this base class instead of creating their own.This section contains two code examples. The first example demonstrates several properties and methods of the Collection class. The second example shows how to derive a collection class from a constructed type of Collection, and how to override the protected methods of Collection to provide custom behavior.
Example 1
The following code example demonstrates many of the properties and methods of Collection. The code example creates a collection of strings, uses the Add method to add several strings, displays the Count, and lists the strings. The example uses the IndexOf method to find the index of a string and the Contains method to determine whether a string is in the collection. The example inserts a string using the Insert method and retrieves and sets strings using the default Item property (the indexer in C#). The example removes strings by string identity using the Remove method and by index using the RemoveAt method. Finally, the Clear method is used to clear all strings from the collection.
Imports System Imports System.Collections.Generic Imports System.Collections.ObjectModel Public Class Demo Public Shared Sub Main() Dim dinosaurs As New Collection(Of String) dinosaurs.Add("Psitticosaurus") dinosaurs.Add("Caudipteryx") dinosaurs.Add("Compsognathus") dinosaurs.Add("Muttaburrasaurus") Console.WriteLine("{0} dinosaurs:", dinosaurs.Count) Display(dinosaurs) Console.WriteLine(vbLf & "IndexOf(""Muttaburrasaurus""): {0}", _ dinosaurs.IndexOf("Muttaburrasaurus")) Console.WriteLine(vbLf & "Contains(""Caudipteryx""): {0}", _ dinosaurs.Contains("Caudipteryx")) Console.WriteLine(vbLf & "Insert(2, ""Nanotyrannus"")") dinosaurs.Insert(2, "Nanotyrannus") Display(dinosaurs) Console.WriteLine(vbLf & "dinosaurs(2): {0}", dinosaurs(2)) Console.WriteLine(vbLf & "dinosaurs(2) = ""Microraptor""") dinosaurs(2) = "Microraptor" Display(dinosaurs) Console.WriteLine(vbLf & "Remove(""Microraptor"")") dinosaurs.Remove("Microraptor") Display(dinosaurs) Console.WriteLine(vbLf & "RemoveAt(0)") dinosaurs.RemoveAt(0) Display(dinosaurs) Console.WriteLine(vbLf & "dinosaurs.Clear()") dinosaurs.Clear() Console.WriteLine("Count: {0}", dinosaurs.Count) End Sub Private Shared Sub Display(ByVal cs As Collection(Of String)) Console.WriteLine() For Each item As String In cs Console.WriteLine(item) Next item End Sub End Class ' This code example produces the following output: ' '4 dinosaurs: ' 'Psitticosaurus 'Caudipteryx 'Compsognathus 'Muttaburrasaurus ' 'IndexOf("Muttaburrasaurus"): 3 ' 'Contains("Caudipteryx"): True ' 'Insert(2, "Nanotyrannus") ' 'Psitticosaurus 'Caudipteryx 'Nanotyrannus 'Compsognathus 'Muttaburrasaurus ' 'dinosaurs(2): Nanotyrannus ' 'dinosaurs(2) = "Microraptor" ' 'Psitticosaurus 'Caudipteryx 'Microraptor 'Compsognathus 'Muttaburrasaurus ' 'Remove("Microraptor") ' 'Psitticosaurus 'Caudipteryx 'Compsognathus 'Muttaburrasaurus ' 'RemoveAt(0) ' 'Caudipteryx 'Compsognathus 'Muttaburrasaurus ' 'dinosaurs.Clear() 'Count: 0
Example 2
The following code example shows how to derive a collection class from a constructed type of the Collection generic class, and how to override the protected InsertItem, RemoveItem, ClearItems, and SetItem methods to provide custom behavior for the Add, Insert, Remove, and Clear methods, and for setting the Item property.
The custom behavior provided by this example is a Changed notification event that is raised at the end of each of the protected methods. The Dinosaurs class inherits Collection<string> (Collection(Of String) in Visual Basic) and defines the Changed event, which uses a DinosaursChangedEventArgs class for the event information, and an enumeration to identify the kind of change.
The code example calls several properties and methods of Collection to demonstrate the custom event.
Imports System Imports System.Collections.Generic Imports System.Collections.ObjectModel Public Class Dinosaurs Inherits Collection(Of String) Public Event Changed As EventHandler(Of DinosaursChangedEventArgs) Protected Overrides Sub InsertItem( _ ByVal index As Integer, ByVal newItem As String) MyBase.InsertItem(index, newItem) RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _ ChangeType.Added, newItem, Nothing)) End Sub Protected Overrides Sub SetItem(ByVal index As Integer, _ ByVal newItem As String) Dim replaced As String = Items(index) MyBase.SetItem(index, newItem) RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _ ChangeType.Replaced, replaced, newItem)) End Sub Protected Overrides Sub RemoveItem(ByVal index As Integer) Dim removedItem As String = Items(index) MyBase.RemoveItem(index) RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _ ChangeType.Removed, removedItem, Nothing)) End Sub Protected Overrides Sub ClearItems() MyBase.ClearItems() RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _ ChangeType.Cleared, Nothing, Nothing)) End Sub End Class ' Event argument for the Changed event. ' Public Class DinosaursChangedEventArgs Inherits EventArgs Public ReadOnly ChangedItem As String Public ReadOnly ChangeType As ChangeType Public ReadOnly ReplacedWith As String Public Sub New(ByVal change As ChangeType, ByVal item As String, _ ByVal replacement As String) ChangeType = change ChangedItem = item ReplacedWith = replacement End Sub End Class Public Enum ChangeType Added Removed Replaced Cleared End Enum Public Class Demo Public Shared Sub Main() Dim dinosaurs As New Dinosaurs AddHandler dinosaurs.Changed, AddressOf ChangedHandler dinosaurs.Add("Psitticosaurus") dinosaurs.Add("Caudipteryx") dinosaurs.Add("Compsognathus") dinosaurs.Add("Muttaburrasaurus") Display(dinosaurs) Console.WriteLine(vbLf & "IndexOf(""Muttaburrasaurus""): {0}", _ dinosaurs.IndexOf("Muttaburrasaurus")) Console.WriteLine(vbLf & "Contains(""Caudipteryx""): {0}", _ dinosaurs.Contains("Caudipteryx")) Console.WriteLine(vbLf & "Insert(2, ""Nanotyrannus"")") dinosaurs.Insert(2, "Nanotyrannus") Console.WriteLine(vbLf & "dinosaurs(2): {0}", dinosaurs(2)) Console.WriteLine(vbLf & "dinosaurs(2) = ""Microraptor""") dinosaurs(2) = "Microraptor" Console.WriteLine(vbLf & "Remove(""Microraptor"")") dinosaurs.Remove("Microraptor") Console.WriteLine(vbLf & "RemoveAt(0)") dinosaurs.RemoveAt(0) Display(dinosaurs) End Sub Private Shared Sub Display(ByVal cs As Collection(Of String)) Console.WriteLine() For Each item As String In cs Console.WriteLine(item) Next item End Sub Private Shared Sub ChangedHandler(ByVal source As Object, _ ByVal e As DinosaursChangedEventArgs) If e.ChangeType = ChangeType.Replaced Then Console.WriteLine("{0} was replaced with {1}", _ e.ChangedItem, e.ReplacedWith) ElseIf e.ChangeType = ChangeType.Cleared Then Console.WriteLine("The dinosaur list was cleared.") Else Console.WriteLine("{0} was {1}.", _ e.ChangedItem, e.ChangeType) End If End Sub End Class ' This code example produces the following output: ' 'Psitticosaurus was Added. 'Caudipteryx was Added. 'Compsognathus was Added. 'Muttaburrasaurus was Added. ' 'Psitticosaurus 'Caudipteryx 'Compsognathus 'Muttaburrasaurus ' 'IndexOf("Muttaburrasaurus"): 3 ' 'Contains("Caudipteryx"): True ' 'Insert(2, "Nanotyrannus") 'Nanotyrannus was Added. ' 'dinosaurs(2): Nanotyrannus ' 'dinosaurs(2) = "Microraptor" 'Nanotyrannus was replaced with Microraptor ' 'Remove("Microraptor") 'Microraptor was Removed. ' 'RemoveAt(0) 'Psitticosaurus was Removed. ' 'Caudipteryx 'Compsognathus 'Muttaburrasaurus
Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
A Collection can support multiple readers concurrently, as long as the collection is not modified. Even so, enumerating through a collection is intrinsically not a thread-safe procedure. To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.
Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.