Vaadin - Iterate over components in a layout

Vaadin 6 / 7 / 8 Framework UI
4

Hi
I use this answer to solve my problem.
But I found the new problem is
When the child components was in HorizontalSplitPanel,
Like :
HorizontalSplitPanel splitPanel = new HorizontalSplitPanel();
Table a=new Table();
a.setId(“A”);

    Table b=new Table();
    b.setId("B");
    splitPanel.addComponents(a,b);

can not find the table “B” ?
just don’t know why?
If I disable to add the table “A” to HorizontalSplitPanel then the table “B” found !

Someone help me !