Why does my TileList selectedIndex not get updated? - apache-flex

Question

In the code below, the presentedAlbumIndex is used to control the selectedIndex of the TileList. Item "five" is initially selected. Whenever the button is pressed the first item in the array is deleted, and the presentedAlbumIndex is decremented.
In theory, the selected index should stay with "five" every time the button is clicked (until "five" is itself deleted). It works this way for the first button press. However, on the 2nd button press the highlighting changes to "six" for some reason. Also, the TileList selectedIndex is always one behind.
Why?
I tried looking into ListBase and monitoring selectedIndex. It looks like the selectedIndex is updated initially to the correct index, but then it reverts back at some point to the correct index+1. I do not know why it's setting back.
It seems it's due to the fact that I am doing a data provider delete and index change in the same operation.
Is there some function in TileList I could override to keep selectedIndex up to date?
Steve
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
layout="absolute"
applicationComplete="init()">
<mx:Label id="label1" text="{'TileList selected index: ' + albumsThumbnailList.selectedIndex}"
x="255" y="55" width="234"/>
<mx:Label id="label2" text="{'Presented album index: ' + presentedAlbumIndex}" x="255" y="81" width="234"/>
<mx:TileList id="albumsThumbnailList" direction="vertical"
dataProvider="{presentedAlbums}"
selectedIndex="{presentedAlbumIndex}" x="25" y="13"
change="presentedAlbumIndex=albumsThumbnailList.selectedIndex"
height="400"/>
<mx:Button click="test2()" x="297" y="150"/>
<mx:Script>
<![CDATA[
import mx.events.CollectionEvent;
import mx.collections.ArrayCollection;
private var _includedAlbums:ArrayCollection = new
ArrayCollection(["zero","one","two","three","four","five","six","seven"]);
[Bindable]
private var presentedAlbumIndex:int = 5;
private function init():void {
_includedAlbums.addEventListener(CollectionEvent.COLLECTION_CHANGE,
function():void {
dispatchEvent(new Event("albumDataChanged"));
}
);
}
public function test2():void {
_includedAlbums.removeItemAt(0);
presentedAlbumIndex--;
}
[Bindable(event="albumDataChanged")]
public function get presentedAlbums():ArrayCollection {
return _includedAlbums;
}
]]>
</mx:Script>
</mx:Application>

Answer 1

With the COLLECTION_CHANGED listener the List gets a new dataProvider, since this is an async event it fires after the binding on the selectedIndex. By removing this listener and not providing a new collection dataProvider whenever the collection changes, the selectedIndex binding functions as expected.
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
layout="absolute"
applicationComplete="init()">
<mx:Label id="label1" text="{'TileList selected index: ' + albumsThumbnailList.selectedIndex}"
x="255" y="55" width="234"/>
<mx:Label id="label2" text="{'Presented album index: ' + presentedAlbumIndex}" x="255" y="81" width="234"/>
<mx:TileList id="albumsThumbnailList" direction="vertical"
dataProvider="{presentedAlbums}" x="25" y="13"
selectedIndex="{presentedAlbumIndex}"
height="400"/>
<mx:Button click="test2()" x="297" y="150"/>
<mx:Script>
<![CDATA[
import mx.events.CollectionEvent;
import mx.collections.ArrayCollection;
private var _includedAlbums:ArrayCollection = new
ArrayCollection(["zero","one","two","three","four","five","six","seven"]);
[Bindable]
private var presentedAlbumIndex:int = 5;
private function init():void {
}
public function test2():void {
_includedAlbums.removeItemAt(0);
presentedAlbumIndex--;
}
[Bindable(event="albumDataChanged")]
public function get presentedAlbums():ArrayCollection {
return _includedAlbums;
}
]]>
</mx:Script>
</mx:Application>