title: Check if delegate still exists before calling respondsToSelector
body: <p>I have made a <code>UIView</code> sub class to deal with iAds and adMob. The view controller is the sub class delegate and everything works ok. Sometimes however, the view controller disappears before the ad has been fetched. To resolve this I set the <code>delegate</code> to <code>nil</code> in my view controller's <code>dealloc</code> implementation.</p>
  
  <p>The problem I have is that sometimes the <code>respondsToSelector:</code> method is ran at the same time as the view controller is getting deallocated. This causes a crash. Does anyone know how I may rearrange this?  </p>
  
  <p>The ad view is on about 10 different view controllers so I would like one place to create the ad code.</p>
  
  <p>Many Thanks</p>