Problem of refreshing a tree in web dynpro java

hi all,

I'm facing a problem for refreshing a tree in web dynpro java for SAP HR.

I created a viewset with 2 cells( 1 view for each).

In the 1st view I created a droplistbyindex to select the unit ID and in the 2nd view ( defaut=false) I called a method to populate my tree according to my selection in the 1st view ( method called in wdInit).

When I make the first selection everything is ok.

But when I select another unit ID, the tree is not changed and I know the context is well changed according to my selection.

So I think the method is executed only the first the view is called.

In this case, how can I refresh my tree on real-time?

Thanks for your help

Yimin