"Bindable" capability does not work in all situations

When I try to set the width of a BorderContainer to a bindable variable in Flex tags declaration it works well. Code looks something like this:

<s:BorderContainer id="mainContent" left="0" right="0" top="0" bottom="0" backgroundAlpha="1" backgroundColor="0xfee6ca" 
                               borderVisible="false">
                <s:layout>
                    <s:VerticalLayout/>
                </s:layout>
      <s:BorderContainer id="containedBc" width={mainContent.width} />
    </s:BorderContainer>

When I try to change the width of "mainContent", the width of "containedBc" is updated also.

But when I try to add t开发者_运维百科he "containedBc" BorderContainer from an actionScript class, the width of "containdBc" does not vary when I try to change mainContent's width. Can you explain me why this? And how to resolve it?

When need to use bindable capability from actionscript3, you can use BindingUtils.bindProperty(...) function. Hope to help you:)