title: is it a good practice to delete the AdBannerView on viewWillDisappear and add it back on viewWillAppear?
body: <p>I am currently doing the following in my code avoid the issue of "obscured" ad. But is it a good practice? One potential problem is that - assume before the viewWillDisappear, there was an ad request send out, and then when the ad come back the adBannerView instance has gone. Would that be a big problem? Should I only do hideAdBanner instead? </p>
  
  <pre><code>- (void)viewWillAppear:(BOOL)animated {
      [super viewWillAppear: animated]; 
  
      // create the ad banner view
      [self createAdBannerView];
  
      if (adBannerView != nil) {
         UIInterfaceOrientation orientation = self.interfaceOrientation;
         [self changeBannerOrientation:orientation];
      }
  } 
  
  - (void)viewWillDisappear:(BOOL)animated { 
      [super viewWillDisappear:animated]; 
  
      // iAd
      if (adBannerView != nil) {
          [self hideAdBanner];
          adBannerView.delegate = nil;
          [adBannerView release];
          adBannerView = nil;
      }
  } 
  </code></pre>