IVirtualLayout

public interface
feathers.layout.IVirtualLayout

Description

A layout algorithm that supports virtualization of items so that only the visible items need to be created. Useful in lists with dozens or hundreds of items are needed, but only a small subset of the items are visible at any given moment.

API overview

Constructor

IVirtualLayout ()

Attributes

Public attributes

typicalItemHeight: Number

The height, in pixels, of a "typical" item that is used to virtually fill in blanks for the layout

typicalItemWidth: Number

The width, in pixels, of a "typical" item that is used to virtually fill in blanks for the layout

useVirtualLayout: Boolean

Determines if virtual layout can be used

Functions

Public functions

getVisibleIndicesAtScrollPosition ( scrollX: Number , scrollY: Number , width: Number , height: Number , itemCount: Number , result: Vector.<Number> = null ): Vector.<Number>

Determines which indices are visible with the specified view port bounds and scroll position

measureViewPort ( itemCount: Number , viewPortBounds: ViewPortBounds = null ): Point

Using the typical item bounds and suggested bounds, returns a set of calculated dimensions for the view port

Constructor

IVirtualLayout ()

Attributes

typicalItemHeight: Number

The height, in pixels, of a "typical" item that is used to virtually fill in blanks for the layout. This value is usually set by a component that is using the layout, such as a List. For instance, the List class provides a typicalItem property that will be used to calculate this value. If you set typicalItemHeight manually, your value will be completely replaced by the value calculated by the List. In other words, you should use that typicalItem property instead.

typicalItemWidth: Number

The width, in pixels, of a "typical" item that is used to virtually fill in blanks for the layout. This value is meant to be set by a component that is using the layout, such as a List. For instance, the List class provides a typicalItem property that will be used to calculate this value. If you set typicalItemWidth manually, your value will be completely replaced by the value calculated by the List. In other words, you should use that typicalItem property instead.

useVirtualLayout: Boolean

Determines if virtual layout can be used. Some components don't support virtual layouts. In those cases, the virtual layout options will be ignored.

Functions

addEventListener ( type: String , listener: Function ): Void
Inherited from IFeathersEventDispatcher

See also:
loom2d.events.EventDispatcher#addEventListener()

Parameters

type: String
listener: Function


dispatchEvent ( event: Event ): Void
Inherited from IFeathersEventDispatcher

See also:
loom2d.events.EventDispatcher#dispatchEvent()

Parameters

event: Event


dispatchEventWith ( type: String , bubbles: Boolean = false , data: Object = null ): Void
Inherited from IFeathersEventDispatcher

See also:
loom2d.events.EventDispatcher#dispatchEventWith()

Parameters

type: String
bubbles: Boolean = false
data: Object = null


getScrollPositionForIndex ( index: Number , items: Vector.<DisplayObject> , x: Number , y: Number , width: Number , height: Number ): Point
Inherited from ILayout

Using the item dimensions, calculates a scroll position that will ensure that the item at a given index will be visible within the specified bounds.

Parameters

index: Number
items: Vector.<DisplayObject>
x: Number
y: Number
width: Number
height: Number


getVisibleIndicesAtScrollPosition ( scrollX: Number , scrollY: Number , width: Number , height: Number , itemCount: Number , result: Vector.<Number> = null ): Vector.<Number>

Determines which indices are visible with the specified view port bounds and scroll position. Indices that aren't returned are typically not displayed and can be replaced virtually.

Parameters

scrollX: Number
scrollY: Number
width: Number
height: Number
itemCount: Number
result: Vector.<Number> = null


hasEventListener ( type: String ): Boolean
Inherited from IFeathersEventDispatcher

See also:
loom2d.events.EventDispatcher#hasEventListener()

Parameters

type: String


layout ( items: Vector.<DisplayObject> , viewPortBounds: ViewPortBounds = null , result: LayoutBoundsResult = null ): LayoutBoundsResult
Inherited from ILayout

Positions (and possibly resizes) the supplied items within the optional bounds argument. If no bounds are specified, the layout algorithm will assume that the bounds start a 0,0 and have unbounded dimensions. Returns the actual bounds of the content, which may be different than the specified bounds.

Note: The items are not absolutely restricted to appear only within the bounds. The bounds can affect positioning, but the algorithm may very well ignore them completely.

If a layout implementation needs to access accurate width and height values from items that are of type IFeathersControl, it must call validate() manually. For performance reasons, the container that is the parent of the items will not call validate() before passing the items to a layout implementation. Meeting this requirement may be as simple as looping through the items at the beginning of layout() and validating all items that are Feathers UI controls:

const itemCount:int = items.length;
for(var i:int = 0; i &lt; itemCount; i++)
{
var item:IFeathersControl = items[i] as IFeathersControl;
if(item)
{
item.validate();
}
}

See also:
feathers.core.IFeathersControl#validate()

Parameters

items: Vector.<DisplayObject>
viewPortBounds: ViewPortBounds = null
result: LayoutBoundsResult = null


measureViewPort ( itemCount: Number , viewPortBounds: ViewPortBounds = null ): Point

Using the typical item bounds and suggested bounds, returns a set of calculated dimensions for the view port.

Parameters

itemCount: Number
viewPortBounds: ViewPortBounds = null


removeEventListener ( type: String , listener: Function ): Void
Inherited from IFeathersEventDispatcher

See also:
loom2d.events.EventDispatcher#removeEventListener()

Parameters

type: String
listener: Function


removeEventListeners ( type: String = null ): Void
Inherited from IFeathersEventDispatcher

See also:
loom2d.events.EventDispatcher#removeEventListeners()

Parameters

type: String = null