title: What is SharedInstance actually?
body: <p>What is sharedInstance actually? I mean what is the usage?</p>
  <p>Currently I'm having some problem in communicating between 2 different files.</p>
  <p>Here's my question:</p>
  <p>I have 1 file call <code>A.h/A.m</code> and another file call <code>B.h/B.m</code>. <code>A.h</code> need to access some of the data in <code>B.h</code>, so .... is there any possible way I could achieve what I want?</p>
  <p>Just wonder is it &quot;SharedInstance&quot; able to solve my problem?</p>