title: change theme on ActionBarActivity on android 4.3 api 18
body: <p>hello i want to change my app theme at runtime, using actionBar compatibility (new api 18) this is my themes:</p>
  
  <pre><code>    &lt;style name="AppThemeDay" parent="@style/Theme.AppCompat.Light"&gt;
        &lt;item name="android:actionBarSize"&gt;....&lt;/item&gt;
      &lt;/style&gt;
  
      &lt;style name="AppThemeNight" parent="@style/Theme.AppCompat"&gt;
        &lt;item name="android:actionBarSize"&gt;...&lt;/item&gt;
      &lt;/style&gt;
  </code></pre>
  
  <p>now i want to change theme into my ActionBarActivity:</p>
  
  <pre><code>if(day){
    setTheme(R.style.AppThemeDay);
  } else{
      setTheme(R.style.AppThemeNight);
  }
  </code></pre>
  
  <p>but i have no change.. why?</p>