title: how to change adapter of a viewpager
body: <p>I'm using a viewpager to display some fragments, now I want to add a button to change the viewpager's content. I try to create some different adapters, and use <code>viewpager.setAdapter()</code> to  use different adapter, but the viewpager display same fragment all the time. </p>
  
  <p>So I want to ask how to change viewpager's display.</p>