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System.Classes.TCollection

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System.Classes.TPersistentSystem.TObjectTCollection

Delphi

TCollection = class(TPersistent)

C++

class PASCALIMPLEMENTATION TCollection : public TPersistent

Properties

Type Visibility Source Unit Parent
class public
System.Classes.pas
System.Classes.hpp
System.Classes System.Classes

Description

TCollection is a container for TCollectionItem objects.

Each TCollection holds a group of TCollectionItem descendants. TCollection maintains an index of the collection items in its Items array. The Count property contains the number of items in the collection. Use the Add and Delete methods to add items to the collection and delete items from the collection.

Objects descended from TCollection can contain objects descended from TCollectionItem. Thus, for each TCollection descendant, there is a corresponding TCollectionItem descendant.

The following table lists some typical descendants of TCollection with the corresponding TCollectionItem descendant and the component that uses each pair:

TCollection descendant TCollectionItem descendant Component

TBitmapLinks

TBitmapLink

TCustomStyleObject

TAggregates

TAggregate

TClientDataSet

TCookieCollection

TCookie

TWebResponse

TCoolBands

TCoolBand

TCoolBar

TDBGridColumns

TColumn

TDBGrid

TDependencies

TDependency

TService

THeaderSections

THeaderSection

THeaderControl

TListColumns

TListColumn

TListView

TParams

TParam

many datasets

TStatusPanels

TStatusPanel

TStatusBar

The controls that use TCollection and TCollectionItem descendants have a published property that holds a collection. (For example, the Panels property of TStatusBar holds a TStatusPanels.) A standard property editor, referred to generically as the Collection editor, can be invoked from the Object Inspector to edit the items in the collection.

Note: When writing a TCollection descendant that is used by another control, be sure to override the protected GetOwner method of the collection so that the descendant class instances can appear in the Object Inspector.
Note: TCollection has the TOwnedCollection descendant that maintains information about its owner. TOwnedCollection implements the GetOwner method. Therefore, classes derived from TOwnedCollection do not need to add anything in order to appear in the Object Inspector.

See Also

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