title: performSelector may cause a leak because its selector is unknown
body: <p>I'm getting the following warning by the ARC compiler:</p>
  
  <pre><code>"performSelector may cause a leak because its selector is unknown".
  </code></pre>
  
  <p>Here's what I'm doing:</p>
  
  <pre><code>[_controller performSelector:NSSelectorFromString(@"someMethod")];
  </code></pre>
  
  <p>Why do I get this warning? I understand the compiler can't check if the selector exists or not, but why would that cause a leak?  And how can I change my code so that I don't get this warning anymore?</p>