title: Weak and strong properties in -viewDidUnload under ARC
body: <p>I am new to iphone development . I am using ARC for my project. As far as I understood using ARC we don't have to release any object manually. But , I have observed in some places , people explicitly set their object to nil in the ViewDidUnload even after using ARC.</p>
  
  <p>For example, in .h file I have something like this:</p>
  
  <pre><code>@property (unsafe_unretained, nonatomic) IBOutlet MKMapView *mapViewOutlet;
  @property (unsafe_unretained, nonatomic) IBOutlet UIToolbar *toolBar;
  @property (strong,nonatomic) NSMutableArray *dataArray;
  </code></pre>
  
  <p>And .m as follows:</p>
  
  <pre><code>- (void)viewDidUnload
  {
       [self setMapViewOutlet:nil];
       [self setToolBar:nil];
       [super viewDidUnload];
       self.dataArray=nil;
  }
  </code></pre>
  
  <p>My question is, is it really necessary to explicitly specify nil in the ViewDidUnload even under ARC?</p>