title: Make the header of the new navigation drawer view clickable
body: <p>My Problem:</p>
  
  <p>I have a <code>MainActivity</code> along with its <code>XML</code> file <code>activity_main.xml</code> , which contains a <code>NavigationDrawer</code> view and that view calls a <code>header.xml</code> file to be displayed in my drawer.</p>
  
  <p>The issue is that my header file contains a button so that when I click the header it opens a site. However since upgrading my <code>Android studio</code> build tools to <code>23.0.2</code> the <code>onClick()</code> for tht button inside my <code>MainActivity</code> crashes the app, giving me a <code>NullPointerException</code>.</p>
  
  <p>I figure that its crashing because the header file is a totally different file from my <code>activity_main.xml</code> so my <code>MainActivity</code> would not have direct access to views inside of the header file.</p>
  
  <p>How can I get access to the button that is inside the <code>header.xml</code> file with and also make it <code>clickable</code>? </p>