Databinding from the Skin to the View in Flex (Spark) - apache-flex

Question

I'm pretty new to Flex development in Spark and wanted to clarify the best way to build components.
I had previously tried to use a binding expression to set the selected index of a ViewStack:
public class MyComponentView extends SkinnableComponent
{
public var selectedIndex:int = 0;
}
<s:Skin ...>
<mx:ViewStack selectedIndex="{hostComponent.selectedIndex}">
....
</mx:ViewStack>
</s:Skin ...>
However, this binding expression doesn't appear to work, although it does show the correct number if I move that binding expression to a s:Label.
In order to get this to work I changed the code thus:
public class MyComponentView extends SkinnableComponent
{
[SkinPart(required = "true")]
public var myStack:ViewStack;
private var _selectedIndex:int = 0;
private var _indexChanged:Boolean;
public function set selectedHistoryIndex(value:int):void
{
_selectedIndex = value;
_indexChanged = true;
invalidateProperties();
}
override protected function partAdded(partName:String, instance:Object):void
{
super.partAdded(partName, instance);
switch (instance)
{
case myStack:
_indexChanged = true;
invalidateProperties();
break;
}
}
override protected function commitProperties():void
{
super.commitProperties();
if (_indexChanged && myStack)
{
_indexChanged = false;
myStack.selectedIndex = _selectedIndex;
}
}
}
<s:Skin ...>
<mx:ViewStack id="myStack">
....
</mx:ViewStack>
</s:Skin ...>
Is this the way I'm meant to do it?

Answer 1

As for me, your second way is more preferable. I'd rather change some code to make it better:
public function set selectedHistoryIndex(value:int):void
{
if (_selectedIndex == value)
return;
_selectedIndex = value;
_indexChanged = true;
invalidateProperties();
}
Yes, you can bind to component's properties from skin but this way View (skins in Spark architecture is for View in MVC and host component is for M and C) has knowledge about M which isn't good. The first implementation requires this knowledge from skin.
The second implementation makes View true View (managed by M). And it is good.