Use focusOut to set things dirty.
Thanks for your quick reply.
I can set the things dirty on focusOut, but my actual problem was focusOut was triggering after tabChange, where I want it to trigger before TabChange event.
For this I have looked into SDK code of tabbar and found that focusEnabled property of renderer(i.e ButtonBarButton) is set to false.
When I change this property to true, it works like a charm.