CollectionBase Class
Provides the abstract base class for a strongly typed collection.
Assembly: mscorlib (in mscorlib.dll)
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.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.