title: How to change background image for navigation item(button)?
body: <p>I want to set background image for every navigation item(button) (universal).</p>
  
  <p>How should these images look?</p>
  
  <p>Are there fixed dimensions or it is possible to create repeating background image?</p>
  
  <p>How to programmatically change then this background image?</p>
  
  <p>Thank's for help</p>
  
  <p>UPDATE:</p>
  
  <p>I found this code for changing background of this button but it's no working.</p>
  
  <pre><code>UIImage *barButton = [UIImage imageNamed:@"button_background.png"];
      [[UIBarButtonItem appearance] setBackgroundImage:barButton forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
  </code></pre>
  
  <p>And I don't know which dimensions should be.</p>
  
  <p>P.S. I want to change background of button just like you can change background color (self.navigation.controller.nvigationBar.tintColor..)</p>