title: Adding a Custom Button to a UINavigationItem LeftBarButtonItem
body: <p>Could anyone tell me why this code does not working?</p>
  
  <pre><code>self.backButton = [UIButton buttonWithType:UIButtonTypeCustom];
  [self.backButton setImage:[UIImage imageNamed:@"back_arrow.png"]
                   forState:UIControlStateNormal];
  self.backButton.contentMode = UIViewContentModeCenter;
  [self.backButton addTarget:self
                      action:@selector(backButtonAction:)
            forControlEvents:UIControlEventTouchUpInside];
  
  UIBarButtonItem *backButtonItem = [[UIBarButtonItem alloc] initWithCustomView:self.backButton];
  [navigationItem setLeftBarButtonItem:backButtonItem animated:NO];
  navigationItem.hidesBackButton = YES;
  </code></pre>
  
  <p>Edit:</p>
  
  <p>Nothing appears on the <code>leftBarButtonItem</code>. That's the problem.</p>