title: Eclipse doesn't generate R.java and gen folder
body: <p>I had to share this problem with you 'cause I lost an entirely morning around this.
  So what was my problem? Suddenly Eclipse refuses to generate R.java and create gen folder. I've tried all kind of solutions I came across in stackoverflow and some blogs:</p>
  
  <ul>
  <li>Clean Project and Rebuild</li>
  <li>Clean Project with Build Automatically off and then Rebuild</li>
  <li>Create the gen folder</li>
  <li>Create gen folder with a R.java dummy</li>
  <li>Copy the gen folder from that project used in another project (different workspaces)</li>
  <li>Validate all my .xml files</li>
  </ul>
  
  <p>Nothing worked...
  So, what was the solution? I'll answer myself.</p>