Determines if the container calls layout() when the scroll position changes. Useful for transforming items as the view port scrolls. This value should be true for layouts that implement the IVirtualLayout interface and the useVirtualLayout property is set to true. May also be used by layouts that toggle item visibility as the items scroll into and out of the view port.

Using the current index and a key press, calculates the new index. This might be use to change a list's selectedIndex when a key is pressed.

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Calculates the scroll position nearest to the current scroll position that will display the full bounds of the item within the view port. If the item is already fully displayed in the view port, the current scroll position will be returned unchanged.

While the item will be displayed in the view port without being clipped in any way, it may not be placed in the most prominent position possible. To give the item a more prominent location, use getScrollPositionForIndex() instead.

This function should always be called after the layout() function. The width and height arguments are the final bounds of the view port, which may be calculated in the layout() function.

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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.

Typically, this function is used to show the item in the most prominent way, such as centering. To scroll a minimum distance required to display the full bounds of the item in the view port, use getNearestScrollPositionForIndex() instead.

This function should always be called after the layout() function. The width and height arguments are the final bounds of the view port, which may be calculated in the layout() function.

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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 < itemCount; i++)
{
    var item:IFeathersControl = items[i] as IFeathersControl;
    if(item)
    {
        item.validate();
    }
}

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Dispatched when a property of the layout changes, indicating that a redraw is probably needed.

The properties of the event object have the following values: