title: Flutter Keyboard listen on hide and show
body: <p>How can I listen whether the keyboard is showing up or hiding?</p>
  
  <p>I tried this example
  <a href="https://stackoverflow.com/questions/47823767/how-to-listen-to-keyboard-on-screen-flutter">How to listen to keyboard on screen Flutter?</a></p>
  
  <pre><code> void _listener(){
      if(_myNode.hasFocus){
        // keyboard appeared 
      }else{
        // keyboard dismissed
      }
  }
  
  FocusNode _myNode = new FocusNode()..addListener(_listner);
  
  TextField _myTextField = new TextField(
          focusNode: _mynNode,
          ...
          ...
      );
  </code></pre>
  
  <p>But unfortunately it doesn't work. Any ideas how it could be possible to listen to the keyboard change?</p>
  
  <p>It seems like it works when I press "Done" on the keyboard. But if i press back on my phone it won't go to "keyboard dismissed" because the focus still exists.. Any help?</p>