This documentation is archived and is not being maintained.

CollectionBase Class

Provides the abstract base class for a strongly typed collection.

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

'Declaration
<SerializableAttribute> _
<ComVisibleAttribute(True)> _
Public MustInherit Class CollectionBase _
	Implements IList, ICollection, IEnumerable
'Usage
Dim instance As CollectionBase

A CollectionBase instance is always modifiable. See ReadOnlyCollectionBase for a read-only version of this class.

The capacity of a CollectionBase is the number of elements the CollectionBase can hold. As elements are added to a CollectionBase, the capacity is automatically increased as required through reallocation. The capacity can be decreased by setting the Capacity property explicitly.

Notes to Implementers:

This base class is provided to make it easier for implementers to create a strongly typed custom collection. Implementers are encouraged to extend this base class instead of creating their own.

The following code example implements the CollectionBase class and uses that implementation to create a collection of Int16 objects.

Imports System
Imports System.Collections


Public Class Int16Collection
   Inherits CollectionBase


   Default Public Property Item(index As Integer) As Int16
      Get 
         Return CType(List(index), Int16)
      End Get 
      Set
         List(index) = value
      End Set 
   End Property 


   Public Function Add(value As Int16) As Integer 
      Return List.Add(value)
   End Function 'Add

   Public Function IndexOf(value As Int16) As Integer 
      Return List.IndexOf(value)
   End Function 'IndexOf


   Public Sub Insert(index As Integer, value As Int16)
      List.Insert(index, value)
   End Sub 'Insert


   Public Sub Remove(value As Int16)
      List.Remove(value)
   End Sub 'Remove


   Public Function Contains(value As Int16) As Boolean 
      ' If value is not of type Int16, this will return false. 
      Return List.Contains(value)
   End Function 'Contains


   Protected Overrides Sub OnInsert(index As Integer, value As Object)
      ' Insert additional code to be run only when inserting values. 
   End Sub 'OnInsert


   Protected Overrides Sub OnRemove(index As Integer, value As Object)
      ' Insert additional code to be run only when removing values. 
   End Sub 'OnRemove


   Protected Overrides Sub OnSet(index As Integer, oldValue As Object, newValue As Object)
      ' Insert additional code to be run only when setting values. 
   End Sub 'OnSet


   Protected Overrides Sub OnValidate(value As Object)
      If Not GetType(System.Int16).IsAssignableFrom(value.GetType()) Then 
         Throw New ArgumentException("value must be of type Int16.", "value")
      End If 
   End Sub 'OnValidate 

End Class 'Int16Collection


Public Class SamplesCollectionBase

   Public Shared Sub Main()

      ' Creates and initializes a new CollectionBase. 
      Dim myI16 As New Int16Collection()

      ' Adds elements to the collection.
      myI16.Add( 1 )
      myI16.Add( 2 )
      myI16.Add( 3 )
      myI16.Add( 5 )
      myI16.Add( 7 )

      ' Display the contents of the collection using For Each. This is the preferred method.
      Console.WriteLine("Contents of the collection (using For Each):")
      PrintValues1(myI16)

      ' Display the contents of the collection using the enumerator.
      Console.WriteLine("Contents of the collection (using enumerator):")
      PrintValues2(myI16)

      ' Display the contents of the collection using the Count property and the Item property.
      Console.WriteLine("Initial contents of the collection (using Count and Item):")
      PrintIndexAndValues(myI16)

      ' Searches the collection with Contains and IndexOf.
      Console.WriteLine("Contains 3: {0}", myI16.Contains(3))
      Console.WriteLine("2 is at index {0}.", myI16.IndexOf(2))
      Console.WriteLine()

      ' Inserts an element into the collection at index 3.
      myI16.Insert(3, 13)
      Console.WriteLine("Contents of the collection after inserting at index 3:")
      PrintIndexAndValues(myI16)

      ' Gets and sets an element using the index.
      myI16(4) = 123
      Console.WriteLine("Contents of the collection after setting the element at index 4 to 123:")
      PrintIndexAndValues(myI16)

      ' Removes an element from the collection.
      myI16.Remove(2)

      ' Display the contents of the collection using the Count property and the Item property.
      Console.WriteLine("Contents of the collection after removing the element 2:")
      PrintIndexAndValues(myI16)

    End Sub 'Main


    ' Uses the Count property and the Item property. 
    Public Shared Sub PrintIndexAndValues(myCol As Int16Collection)
      Dim i As Integer 
      For i = 0 To myCol.Count - 1
          Console.WriteLine("   [{0}]:   {1}", i, myCol(i))
      Next i
      Console.WriteLine()
    End Sub 'PrintIndexAndValues


    ' Uses the For Each statement which hides the complexity of the enumerator. 
    ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection. 
    Public Shared Sub PrintValues1(myCol As Int16Collection)
      Dim i16 As Int16
      For Each i16 In  myCol
          Console.WriteLine("   {0}", i16)
      Next i16
      Console.WriteLine()
    End Sub 'PrintValues1


    ' Uses the enumerator.  
    ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection. 
    Public Shared Sub PrintValues2(myCol As Int16Collection)
      Dim myEnumerator As System.Collections.IEnumerator = myCol.GetEnumerator()
      While myEnumerator.MoveNext()
          Console.WriteLine("   {0}", myEnumerator.Current)
      End While
      Console.WriteLine()
    End Sub 'PrintValues2

End Class 'SamplesCollectionBase


'This code produces the following output. 

'Contents of the collection (using For Each): 
'   1 
'   2 
'   3 
'   5 
'   7 

'Contents of the collection (using enumerator): 
'   1 
'   2 
'   3 
'   5 
'   7 

'Initial contents of the collection (using Count and Item): 
'   [0]:   1 
'   [1]:   2 
'   [2]:   3 
'   [3]:   5 
'   [4]:   7 

'Contains 3: True 
'2 is at index 1. 

'Contents of the collection after inserting at index 3: 
'   [0]:   1 
'   [1]:   2 
'   [2]:   3 
'   [3]:   13 
'   [4]:   5 
'   [5]:   7 

'Contents of the collection after setting the element at index 4 to 123: 
'   [0]:   1 
'   [1]:   2 
'   [2]:   3 
'   [3]:   13 
'   [4]:   123 
'   [5]:   7 

'Contents of the collection after removing the element 2: 
'   [0]:   1 
'   [1]:   3 
'   [2]:   13 
'   [3]:   123 
'   [4]:   7

System.Object
  System.Collections.CollectionBase
    Microsoft.ManagementConsole.BaseCollection
    System.CodeDom.CodeAttributeArgumentCollection
    System.CodeDom.CodeAttributeDeclarationCollection
    System.CodeDom.CodeCatchClauseCollection
    System.CodeDom.CodeCommentStatementCollection
    System.CodeDom.CodeDirectiveCollection
    System.CodeDom.CodeExpressionCollection
    System.CodeDom.CodeNamespaceCollection
    System.CodeDom.CodeParameterDeclarationExpressionCollection
    System.CodeDom.CodeStatementCollection
    System.CodeDom.CodeTypeDeclarationCollection
    System.CodeDom.CodeTypeMemberCollection
    System.CodeDom.CodeTypeParameterCollection
    System.CodeDom.CodeTypeReferenceCollection
    System.CodeDom.Compiler.CompilerErrorCollection
    System.ComponentModel.Design.Data.DataSourceDescriptorCollection
    System.ComponentModel.Design.Data.DataSourceGroupCollection
    System.ComponentModel.Design.DesignerActionItemCollection
    System.ComponentModel.Design.DesignerActionListCollection
    System.ComponentModel.Design.DesignerVerbCollection
    System.Configuration.Install.InstallerCollection
    System.Data.SqlClient.SqlBulkCopyColumnMappingCollection
    System.Diagnostics.CounterCreationDataCollection
    System.Diagnostics.EventLogPermissionEntryCollection
    System.Diagnostics.PerformanceCounterPermissionEntryCollection
    System.DirectoryServices.ActiveDirectory.ActiveDirectorySchemaClassCollection
    System.DirectoryServices.ActiveDirectory.ActiveDirectorySchemaPropertyCollection
    System.DirectoryServices.ActiveDirectory.ActiveDirectorySiteCollection
    System.DirectoryServices.ActiveDirectory.ActiveDirectorySiteLinkCollection
    System.DirectoryServices.ActiveDirectory.ActiveDirectorySubnetCollection
    System.DirectoryServices.ActiveDirectory.DirectoryServerCollection
    System.DirectoryServices.DirectoryServicesPermissionEntryCollection
    System.DirectoryServices.PropertyValueCollection
    System.DirectoryServices.Protocols.DirectoryAttribute
    System.DirectoryServices.Protocols.DirectoryAttributeCollection
    System.DirectoryServices.Protocols.DirectoryAttributeModificationCollection
    System.DirectoryServices.Protocols.DirectoryControlCollection
    System.Messaging.AccessControlList
    System.Messaging.MessageQueuePermissionEntryCollection
    System.Security.Cryptography.X509Certificates.X509CertificateCollection
    System.ServiceProcess.ServiceControllerPermissionEntryCollection
    System.Web.ParserErrorCollection
    System.Web.Services.Description.BasicProfileViolationCollection
    System.Web.Services.Description.MimePartCollection
    System.Web.Services.Description.MimeTextMatchCollection
    System.Web.Services.Description.ServiceDescriptionBaseCollection
    System.Web.Services.Description.WebReferenceCollection
    System.Web.Services.Discovery.DiscoveryClientResultCollection
    System.Web.Services.Discovery.DiscoveryReferenceCollection
    System.Web.Services.Protocols.SoapHeaderCollection
    System.Web.UI.WebControls.EmbeddedMailObjectsCollection
    System.Web.UI.WebControls.RoleGroupCollection
    System.Web.UI.WebControls.WebParts.ProxyWebPartConnectionCollection
    System.Web.UI.WebControls.WebParts.WebPartConnectionCollection
    System.Web.UI.WebControls.WebParts.WebPartDisplayModeCollection
    System.Web.UI.WebControls.WebParts.WebPartTransformerCollection
    System.Windows.Documents.LinkTargetCollection
    System.Windows.Forms.Design.Behavior.BehaviorServiceAdornerCollection
    System.Windows.Forms.Design.Behavior.GlyphCollection
    System.Xml.Schema.XmlSchemaObjectCollection
    System.Xml.Serialization.Advanced.SchemaImporterExtensionCollection
    System.Xml.Serialization.XmlAnyElementAttributes
    System.Xml.Serialization.XmlArrayItemAttributes
    System.Xml.Serialization.XmlElementAttributes
    System.Xml.Serialization.XmlSchemas

Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

This implementation does not provide a synchronized (thread safe) wrapper for a CollectionBase, but derived classes can create their own synchronized versions of the CollectionBase using the SyncRoot property.

Enumerating through a collection is intrinsically not a thread safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
Show: