title: Button setOnClickListener causing application crash
body: <p>So I have 2 XML layout files.<br/>
  One is the menu and the other is the app.<br/>
  So, now I have some buttons on the one XML file and some other buttons on the other file.</p>
  
  <p>So this code works:</p>
  
  <pre><code>    setContentView(R.layout.main);
      start = (Button) findViewById(R.id.button1);
  
      start.setOnClickListener(this);
  </code></pre>
  
  <p>But if I change the view and write this:</p>
  
  <pre><code>    setContentView(R.layout.random);
      add_person = (Button) findViewById(R.id.add);
  
      add_person.setOnClickListener(this); //crash here
  </code></pre>
  
  <p>The app crashes! </p>