title: keyboardWillShow called twice
body: <p>I have a view with keyboard notifications such as <code>keyboardWillShow</code> and <code>keyboardWillHide</code></p>
  
  <p>All the codes handles with the notification I use is taken from Apple's sample code <a href="http://developer.apple.com/library/ios/#samplecode/KeyboardAccessory/Introduction/Intro.html#//apple_ref/doc/uid/DTS40009462">"KeyboardAccessory"</a></p>
  
  <p>When I first enter this view, everything works fine.</p>
  
  <p>But when I return to this view from its subviews, every time I tap a button that says:</p>
  
  <pre><code>[myTextField becomeFirstResponder];
  </code></pre>
  
  <p>the <code>keyboardWillShow</code> and <code>keyboardWillHide</code> methods will be called twice every time.</p>
  
  <p>It's really confusing,</p>
  
  <p>Could anyone helps me with this?</p>
  
  <p>really appreciate!</p>