title: Is it possible to cancel PerformSelector on multiple objects?
body: <p>I have a few classes that can call performSelector:afterDelay.</p>
  
  <p>In some circumstances I want to cancel any and all of them. </p>
  
  <p>However all the cancelPerformSelector type methods take a target, thus it would seem there is no way to cancel everything in one go (as there are different targets)?</p>
  
  <p>Unless specifying nil as the target will cancel everything? </p>
  
  <p>Or could the target be specified as [NSRunLoop mainRunLoop] to cancel everything such as</p>
  
  <pre><code>[NSObject cancelPreviousPerformRequestsWithTarget:[NSRunLoop mainRunLoop]]
  </code></pre>