Flex 2 Developer's Guide > Building User Interfaces for
Flex Applications > Using Data Providers and Collections > About data providers and collections > About collections

About collections

A collection provides a uniform method to access and represent a data provider's data. The collection creates a level of abstraction between Flex components and the data that you use to populate them. The collection interfaces and implementations provide the following features:

They ensure that a control is properly updated when the underlying data changes. Controls do not update when non-collection data providers change. (They do update to reflect the new data the next time they are refreshed.) If the data provider is a collection, the controls update immediately after the collection change occurs.
They provide mechanisms for handling paged data coming from remote data providers that may not initially be available and may arrive over a period of time.
They provide a consistent set of operations on the data, independent of those provided by the raw data provider objects. For example, you could create a custom class that implements the IList interface and lets you insert and delete objects by using an index into the collection, independent of whether the underlying data is, for example, in an array or an object.
Collections that conform to the ICollectionView interface provide a specific view of the data that can be in sorted order, or filtered by a developer-supplied method. These limitations affect only the collection's view, and do not change the underlying data.
You can use a single collection to populate multiple components from the same data provider.
You can use collections to switch data providers for a component at run time, and to modify a data provider so that changes are reflected by all components that use the data provider.
You can use collection methods to access data in the underlying data object.

NOTE

If you use a raw object, such as an Array, as a control's data provider, Flex automatically wraps the object in a collection wrapper. The control does not automatically detect changes that are made directly to the raw object. A change in the length of an array, for example, does not result in an update of the control. You can, however, use an object proxy, a listener interface, or the itemUpdated property to notify the view of certain changes.

Subtopics

Collection interfaces

Collection classes

Collection interfaces

The Flex framework collection model uses these interfaces to define how a collection represents data and provides access to it:

Interface	Description
IList	A direct representation of items organized in an ordinal fashion. The interface presents the data from the data provider in the same order as it exists in the provider, and provides access and manipulation methods based on an index. The IList class does not provide sorting, filtering, or cursor functionality.
ICollectionView	A view of a collection of items. You can modify the view to show the data in sorted order and to show a subset of the items in the data provider, as specified by a filter function. A class that implements this interface can use an IList interface as the underlying collection. The interface provides access to an IViewCursor object for access to the items.
IViewCursor	Enumerates an ICollectionView object bidirectionally. The view cursor provides find, seek, and bookmarking capabilities, and lets you modify the underlying data (and the view) by inserting and removing items.

Interface

Description

IList

A direct representation of items organized in an ordinal fashion. The interface presents the data from the data provider in the same order as it exists in the provider, and provides access and manipulation methods based on an index. The IList class does not provide sorting, filtering, or cursor functionality.

ICollectionView

A view of a collection of items. You can modify the view to show the data in sorted order and to show a subset of the items in the data provider, as specified by a filter function. A class that implements this interface can use an IList interface as the underlying collection.

The interface provides access to an IViewCursor object for access to the items.

IViewCursor

Enumerates an ICollectionView object bidirectionally. The view cursor provides find, seek, and bookmarking capabilities, and lets you modify the underlying data (and the view) by inserting and removing items.

The IList and ICollectionView interfaces provide two alternate methods for accessing and changing data. The IList interface is simpler; it provides add, set, get, and remove operations that operate directly on linear data.

The ICollectionView interface (also called the collection view) provides a more complex set of operations than the IList interface, and is appropriate when the underlying data may not be organized linearly. Its data access techniques, however, are more complex than those of the IList interface, so you should use the IList interface if you need only simple, indexed access to a linear collection. The collection view can represent a subset of the underlying data, as determined by a sort or filter operation.

The standard Flex collection classes, ArrayCollection and XMLListCollection, implement both the collection view (ICollectionView) interface and the IList interface.

For information on using the IList interface methods and property, see Using IList interface methods and properties. For information on using the ICollectionView interface methods and properties, Including the IViewCursor object that the interface exposes, see Using ICollectionView interface methods and properties.

Collection classes

The following table describes the public classes in the mx.collections package. It does not include constant classes, event and error classes. For complete reference information on collection-related classes, see the collections and collections.errors packages, and the CollectionEvent and CollectionEventKind classes in Adobe Flex 2 Language Reference.

Class	Description
ArrayCollection	Implements the IList and ICollectionView interfaces for use with array-based data providers.
XMLListCollection	Implements the IList and ICollectionView interfaces, and a subset of XMLList methods for use with XML-based data providers.
CursorBookmark	Represents the position of an IViewCursor instance within an ICollectionView instance. You can save a view cursor position in a CursorBookmark object and use the object to return the view cursor to the position at a later time.
Sort	Provides the information and methods required to sort an ICollectionView instance.
SortField	Provides properties and methods that determine how a specific field affects how data is sorted in an ICollectionView instance.
ItemResponder	(Used only if the data source is remote.) Handles cases when requested data is not yet available.
ListCollectionView	Adapts an object that implements the IList interface to the ICollectionView interface so that it can be passed to anything that expects an IList or an ICollectionView. This class is the superclass of the ArrayCollection and XMLListCollection classes

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