mx.collections.AsyncListView - Adobe® Flex® 4 Language Reference (Flex 4)

Package	mx.collections
Class	public class AsyncListView
Inheritance	AsyncListView OnDemandEventDispatcher Object
Implements	IList

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

The AsyncListView class is an implementation of the IList interface that handles ItemPendingErrors errors thrown by the getItemAt(), removeItemAt(), and toArray() methods.

The getItemAt() method handles ItemPendingErrors by returning a provisional "pending" item until the underlying request succeeds or fails. The provisional item is produced by calling the function specified by the createPendingItemFunction property. . If the request succeeds, the actual item replaces the provisional one. If it fails, the provisional item is replaced with the item returned by calling the function specified by the createFailedItemFunction property.

This class delegates the IList methods and properties to its list. If a list isn't specified, methods that mutate the collection are no-ops, and methods that query the collection return an empty value, such as null or zero as appropriate.

This class is intended to be used with Spark components based on DataGroup, such as List and ComboBox. The Spark classes do not provide intrinsic support for ItemPendingError handling.

AsyncListView does not support re-insertion of pending or failed items. Once a failed or pending item is removed, its connection to a pending request for data is lost. Using drag and drop to move a pending item in an ASyncListView, or sorting an ASyncListView that contains pending or failed items, is not supported because these operations remove and then re-insert list items.

MXML Syntax expanded

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The <mx:AsyncListView> tag inherits all the attributes of its superclass, and adds the following attributes:

  <mx:AsyncListView
  Properties
    createFailedItemFunction="null"
    createPendingItemFunction="null"
    list="null"
  />

Public Properties

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	Property		Defined By
		constructor : Object A reference to the class object or constructor function for a given object instance.	Object
		createFailedItemFunction : Function A callback function used to create a substitute item when a request which had caused an ItemPendingError to be thrown, subsequently fails.	AsyncListView
		createPendingItemFunction : Function A callback function used to create a provisional item when the initial request causes an ItemPendingError to be thrown.	AsyncListView
		length : int [read-only] The number of items in this collection.	AsyncListView
		list : IList The IList object that this collection wraps.	AsyncListView
		prototype : Object [static] A reference to the prototype object of a class or function object.	Object

Public Methods

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	Method		Defined By
		AsyncListView(list:IList = null) Constructor.	AsyncListView
		addEventListener(type:String, listener:Function, useCapture:Boolean = false, priority:int = 0, useWeakReference:Boolean = false):void	OnDemandEventDispatcher
		addItem(item:Object):void Adds the specified item to the end of the list.	AsyncListView
		addItemAt(item:Object, index:int):void Adds the item at the specified index.	AsyncListView
		dispatchEvent(event:Event):Boolean	OnDemandEventDispatcher
		getItemAt(index:int, prefetch:int = 0):Object Returns the value of list.getItemAt(index).	AsyncListView
		getItemIndex(item:Object):int Returns the index of the item if it is in the list such that getItemAt(index) == item.	AsyncListView
		hasEventListener(type:String):Boolean	OnDemandEventDispatcher
		hasOwnProperty(name:String):Boolean Indicates whether an object has a specified property defined.	Object
		isPrototypeOf(theClass:Object):Boolean Indicates whether an instance of the Object class is in the prototype chain of the object specified as the parameter.	Object
		itemUpdated(item:Object, property:Object = null, oldValue:Object = null, newValue:Object = null):void Notifies the view that an item has been updated.	AsyncListView
		propertyIsEnumerable(name:String):Boolean Indicates whether the specified property exists and is enumerable.	Object
		removeAll():void Removes all items from the list.	AsyncListView
		removeEventListener(type:String, listener:Function, useCapture:Boolean = false):void	OnDemandEventDispatcher
		removeItemAt(index:int):Object Removes the actual or pending item at the specified index and returns it.	AsyncListView
		setItemAt(item:Object, index:int):Object Places the item at the specified index.	AsyncListView
		setPropertyIsEnumerable(name:String, isEnum:Boolean = true):void Sets the availability of a dynamic property for loop operations.	Object
		toArray():Array Returns an array with the same elements as this AsyncListView.	AsyncListView
		toLocaleString():String Returns the string representation of this object, formatted according to locale-specific conventions.	Object
		toString():String Returns a string that contains the list's length and the number of pending item requests.	AsyncListView
		valueOf():Object Returns the primitive value of the specified object.	Object
		willTrigger(type:String):Boolean	OnDemandEventDispatcher

Events

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	Event		Summary	Defined By
		collectionChange	Dispatched when the list's length has changed or when a list element is replaced.	AsyncListView

Property Detail

createFailedItemFunction

property

createFailedItemFunction:Function

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

A callback function used to create a substitute item when a request which had caused an ItemPendingError to be thrown, subsequently fails. The existing item, typically a pending item created by the callback function specified by the createPendingItemFunction() property, is replaced with the failed item.

The value of this property must be a function with two parameters: the index of the requested item, and the failure "info" object, which is passed along from the IResponder fault() method. In most cases you can ignore the second parameter. Shown below is an example implementation of the callback function:

     function createFailedItem(index:int, info:Object):Object
     {
         return "[" + index + "request failed]";        
     }

Setting this property does not affect failed items that were already created. Setting this property to null prevents failed items from being created.

The default value is A function that unconditionally returns null..

Implementation
public function get createFailedItemFunction():Function
public function set createFailedItemFunction(value:Function):void

createPendingItemFunction

property

createPendingItemFunction:Function

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

A callback function used to create a provisional item when the initial request causes an ItemPendingError to be thrown. If the request eventually succeeds, the provisional item is automatically replaced by the actual item. If the request fails, then the item is replaced with one created with the callback function specified by the createFailedItemFunction property.

The value of this property must be a function with two parameters: the index of the requested data provider item, and the ItemPendingError itself. In most cases, the second parameter can be ignored. The following example shows an implementation of the callback function:

     function createPendingItem(index:int, ipe:ItemPendingError):Object
     {
         return "[" + index + "request is pending...]";        
     }

Setting this property does not affect provisional pending items that were already created. Setting this property to null prevents provisional pending items from being created.

The default value is A function that unconditionally returns null..

Implementation
public function get createPendingItemFunction():Function
public function set createPendingItemFunction(value:Function):void

length

property

length:int [read-only]

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

The number of items in this collection. 0 means no items while -1 means the length is unknown.

This property can be used as the source for data binding. When this property is modified, it dispatches the collectionChange event.

Implementation
public function get length():int

list

property

list:IList

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

The IList object that this collection wraps. That means the object to which all of the IList methods are delegated.

If this property is null, the IList mutation methods, such as setItemAt(), are no-ops. The IList query methods, such getItemAt(), return null or zero (-1 for getItemIndex()), as appropriate.

The default value is null.

This property can be used as the source for data binding. When this property is modified, it dispatches the listChanged event.

Implementation
public function get list():IList
public function set list(value:IList):void

Constructor Detail

AsyncListView

()

Constructor

public function AsyncListView(list:IList = null)

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Constructor.

Parameters

list:IList (default = null) — Initial value of the list property, the IList we're delegating to.

Method Detail

addItem

()

method

public function addItem(item:Object):void

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Adds the specified item to the end of the list. Equivalent to addItemAt(item, length).

Parameters

item:Object — The item to add.

addItemAt

()

method

public function addItemAt(item:Object, index:int):void

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Adds the item at the specified index. The index of any item greater than the index of the added item is increased by one. If the the specified index is less than zero or greater than the length of the list, a RangeError is thrown.

Parameters

	`item:Object` — The item to place at the index.

	`index:int` — The index at which to place the item.

getItemAt

()

method

public function getItemAt(index:int, prefetch:int = 0):Object

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Returns the value of list.getItemAt(index).

This method catches ItemPendingErrors (IPEs) generated as a consequence of calling getItemAt(). If an IPE is thrown, an IResponder is added to the IPE and a provisional "pending" item, created with the createPendingItemFunction is returned. If the underlying request eventually succeeds, the pending item is replaced with the real item. If it fails, the pending item is replaced with a value produced by calling createFailedItemFunction.

Parameters

	`index:int` — The list index from which to retrieve the item.

	`prefetch:int` (default = `0`) — An `int` indicating both the direction and number of items to fetch during the request if the item is not local.

Returns

Object — The list item at the specified index.

Throws

RangeError — if index < 0 or index >= length.

getItemIndex

()

method

public function getItemIndex(item:Object):int

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Returns the index of the item if it is in the list such that getItemAt(index) == item.

Note: unlike IViewCursor.findxxx() methods, The getItemIndex() method cannot take a parameter with only a subset of the fields in the item being serched for; this method always searches for an item that exactly matches the input parameter.

Parameters

item:Object — The item to find.

Returns

int — The index of the item, or -1 if the item is not in the list.

itemUpdated

()

method

public function itemUpdated(item:Object, property:Object = null, oldValue:Object = null, newValue:Object = null):void

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Notifies the view that an item has been updated. This is useful if the contents of the view do not implement IEventDispatcher and dispatches a PropertyChangeEvent. If a property is specified the view may be able to optimize its notification mechanism. Otherwise it may choose to simply refresh the whole view.

Parameters

	`item:Object` — The item within the view that was updated.

	`property:Object` (default = `null`) — The name of the property that was updated.

	`oldValue:Object` (default = `null`) — The old value of that property. (If property was null, this can be the old value of the item.)

	`newValue:Object` (default = `null`) — The new value of that property. (If property was null, there's no need to specify this as the item is assumed to be the new value.)

removeAll

()

method

public function removeAll():void

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Removes all items from the list.

If any item is not local and an asynchronous operation must be performed, an ItemPendingError will be thrown.

See the ItemPendingError documentation as well as the collections documentation for more information on using the ItemPendingError.

removeItemAt

()

method

public function removeItemAt(index:int):Object

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Removes the actual or pending item at the specified index and returns it. All items whose index is greater than the specified index have their index reduced by 1.

If there is no actual or pending item at the specified index, for example because a call to getItemAt(index) hasn't caused the data to be paged in, then the underlying list may throw an ItemPendingError. The implementation ignores the ItemPendingError and returns null.

Parameters

index:int — The list index from which to retrieve the item.

Returns

Object — The item that was removed or null.

Throws

RangeError — if index < 0 or index >= length.

setItemAt

()

method

public function setItemAt(item:Object, index:int):Object

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Places the item at the specified index. If an item was already at that index the new item will replace it and it will be returned.

Parameters

	`item:Object` — The new item to be placed at the specified index.

	`index:int` — The index at which to place the item.

Returns

Object — The item that was replaced, or null if none.

toArray

()

method

public function toArray():Array

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Returns an array with the same elements as this AsyncListView. The array is initialized by retrieving each item with getItemAt(), so pending items are substituted where actual values aren't available yet. The array will not be updated when the AsyncListView replaces the pending items with actual (or failed) values.

Returns

Array — an array with the same elements as this AsyncListView.

toString

()

method

public function toString():String

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

Returns a string that contains the list's length and the number of pending item requests. It does not trigger pending requests.

Returns

String — A brief description of the list.

Event Detail

collectionChange

Event

Event Object Type: mx.events.CollectionEvent
property CollectionEvent.type = mx.events.CollectionEvent.COLLECTION_CHANGE

Language Version:

ActionScript 3.0

Product Version:

Flex 3

Runtime Versions:

Flash Player 9, AIR 1.1

Dispatched when the list's length has changed or when a list element is replaced.

The CollectionEvent.COLLECTION_CHANGE constant defines the value of the type property of the event object for an event that is dispatched when a collection has changed.

The properties of the event object have the following values. Not all properties are meaningful for all kinds of events. See the detailed property descriptions for more information.

Property	Value
`bubbles`	false
`cancelable`	false
`currentTarget`	The Object that defines the event listener that handles the event. For example, if you use `myButton.addEventListener()` to register an event listener, myButton is the value of the `currentTarget`.
`items`	An Array of objects with information about the items affected by the event. The contents of this field depend on the event kind; for details see the `items` property
`kind`	The kind of event. The valid values are defined in the CollectionEventKind class as constants.
`location`	Location within the target collection of the item(s) specified in the `items` property.
`oldLocation`	the previous location in the collection of the item specified in the `items` property.
`target`	The Object that dispatched the event; it is not always the Object listening for the event. Use the `currentTarget` property to always access the Object listening for the event.
`type`	CollectionEvent.COLLECTION_CHANGE