Using VerticalSpinnerLayout in the Feathers SpinnerList component (AS3/Starling version)

The VerticalSpinnerLayout class may be used by the SpinnerList component to display items from top to bottom in a single column, repeating items infinitely if the number of items in the data provider allows for it. It supports a number of useful options for adjusting the spacing and alignment.

The Basics

First, let's create a VerticalSpinnerLayout and pass it to a SpinnerList:

var layout:VerticalSpinnerLayout = new VerticalSpinnerLayout();
 
var list:SpinnerList = new SpinnerList();
list.layout = layout;
this.addChild( list );

There are a number of simple properties that may be used to affect the layout. The most common are padding and gap.

The padding is the space around the content that the layout positions and sizes. You may set padding on the left and right sides of the container separately. Below, we set the paddingLeft to 10 pixels and the paddingRight to 15 pixels:

layout.paddingRight = 15;
layout.paddingLeft = 10;

The gap is the space between items. Let's set the gap property to 5 pixels:

layout.gap = 5;

We can align the items in the layout using the horizontalAlign property. Let's adjust it so that the content will be aligned to the center:

layout.horizontalAlign = HorizontalAlign.CENTER;

Virtual Vertical Spinner Layout

In a SpinnerList, the layout may be virtualized, meaning that some items in the layout will not actually exist if they are not visible. This helps to improve performance of a scrolling list because only a limited number of item renderers will be created at any given moment. If the list's data provider is very large, a virtual layout is essential, even on desktop computers that have incredible processing power compared to mobile devices.

A virtualized layout will need as estimate about how big a "virtual" item renderer should be. You should set the typicalItem property of the list to have it determine the typical width and height of an item renderer to use as this estimated value. If you don't pass in a typical item, the first item in the data provider is used for this estimate.

By default useVirtualLayout is true for containers that support it. You may disable virtual layouts by setting it to false. When a layout is not virtualized, every single item renderer must be created by the component. If a list has thousands of items, this means that thousands of item renderers need to be created. This can lead to significant performance issues, especially on mobile. In general, you should rarely disable useVirtualLayout.

layout.useVirtualLayout = false;