what event triggered when a page themes changed

Hi all what event triggered when a page themes changed at dynamically? i faced this question in an interview..

ex: In orkut when we press the themes link/button we can ge开发者_如何学JAVAt what we wanted..

thanks saj

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In addition to Microgen's comment here is a link for you to see a solution.

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There is no event specific for changing the page theme because the theme can only be changed inside the Page's PreInit event.