title: Android: Why do we need to use R2 instead of R with butterknife?
body: <p>I've been using <a href="https://github.com/JakeWharton/butterknife" rel="noreferrer">butterknife</a> for a few months and I've just noticed in its documentation that it says:</p>
  
  <blockquote>
    <p>Now make sure you use R2 instead of R inside all Butter Knife
    annotations.</p>
  </blockquote>
  
  <p>Why is that? I've been using R and everything works perfect.</p>