Flex: Spark List's Indeces in View change on Orientation Change - list

Question

I have a spark list with a variable row_height (2 custom itemRenderer: Header 30 px, Contact 60 px) that on the only first orientation change after a scroll, change the indexes in view.
I tried to set Header to be 60 px height, and i had no problems with the orientation change.
I'm not setting the verticalScrollPosition anywhere. Adding an event listener on the viewport's list and watching the verticalScrollPosition, it doesn't change on orientation change.
I really don't know how can i fix that.
EDIT:
This is the code relative to the list:
<fx:Script>
protected function creationCompleteHandler(event:FlexEvent):void
{
addressBookViewModel = ViewModelFactory.getInstance().getAddressBookViewModel();
addressBookViewModel.getUserContacts(onDataReceived);
}
protected function pagedContactsList_initializeHandler(event:FlexEvent):void
{
asyncListView.list = pagedContactsList;
}
private function onDataReceived():void
{
pagedContactsList.length = (BusinessContext.getInstance().getTotalContacts() + BusinessContext.getInstance().getTotalLastNames());
loadPagedData();
}
private function createPendingItemFunctionHandler(index:int, ipe:ItemPendingError):Object
{
if(!addressBookViewModel.pageUp)
{
addressBookViewModel.pageUp = true;
addressBookViewModel.currentPage++;
addressBookViewModel.getMoreUserContacts(onMoreDataRecieved, onMoreDataMissing);
}
return loadingDataHeader;
}
private function onMoreDataRecieved():void
{
loadPagedData();
}
private function loadPagedData():void
{
for(var i:int = 0; i < addressBookViewModel.contacts.length; i++)
{
pagedContactsList.setItemAt(addressBookViewModel.contacts.getItemAt(i), pagedContactsList.lastItemInsertedIndex);
pagedContactsList.lastItemInsertedIndex++;
}
addressBookViewModel.pageUp = false;
}
internal var headerItemRender:ClassFactory = new ClassFactory(HeaderItemRenderer);
internal var contactItemRenderer:ClassFactory = new ClassFactory(ContactItemRenderer);
private function rendererFunction(item:Object):ClassFactory
{
return item.hasOwnProperty("isHeader") ? headerItemRender : contactItemRenderer;
}
</fx:Script>
<fx:Declarations>
<custom:PagedArrayList id="pagedContactsList" initialize="pagedContactsList_initializeHandler(event)"/>
</fx:Declarations>
<s:List id="list" width="100%"
height="100%" itemRendererFunction="rendererFunction" change="list1_changeHandler(event)">
<s:AsyncListView id="asyncListView" createPendingItemFunction="createPendingItemFunctionHandler" />
</s:List>
The curious thing is that before and after the orientation change the list.scroller.viewport.verticalScrollPosition has the same value even if the list has scrolled ~ 40 rows. (40 is the page size).
I have many lists in my app, and every list that has const row_height has no issue, but the 2 with a variable row_height have this problem. Maybe it's caused by the AsyncListView.
EDIT 2:
I removed the AsyncListView, binding directly addressBookViewModel.contacts to the list.dataProvider, removing the pagination and the issue is still there.
EDIT 3:
I think that the only thing to do is to put breakpoints everywhere in the Scroller's class.
EDIT 4:
This issue happens only when scrolling to the bottom of the list.
EDIT 5:
Find the issue!
VerticalLayout.as, in updateDisplayListVirtual(row 1797) there's a call to a method (updateLLV) that set up a LinearLayoutVector using a typicalLayoutElement. This is lazily init with the first itemRenderer added to the dataGroup of the list. In my case it's the HeaderItemRenderer (30px).
After the updateLLV, the startIndex (index of the first visible item) is setted by calling the indexOf on the LinearLayoutVector and passing the verticalScrollPosition. (briefly: verticalScrollPosition / typicalLayoutElement.height)
The problem is that nowhere is taken into consideration the variableRowHeight!

Answer 1

Workaround found! Not so elegant, but it works.
stage.eventListener(StageOrientationEvent.ORIENTATION_CHANGING, yourReorientHandler, false, 1)
Setting the priority is really important, otherwise the updateDisplayListVirtual will be called before your handler.
private function reorientHandler(event:StageOrientationEvent):void
{
var IndecesInView:Vector.<int> = list.dataGroup.getItemIndicesInView();
var firstInView:int = IndecesInView[0];
callLater(
function():void
{
if(!list.layout.getScrollPositionDeltaToElement(firstInView+1)) return;
list.scroller.viewport.verticalScrollPosition += list.layout.getScrollPositionDeltaToElement(firstInView+1).y;
});
}