title: extjs4 get selected value from combobox
body: <p>Ok, this is driving me nuts again. I am trying to get the selected value from a combo box so I can update a grid with the correct data based on the user selection. How do I do this?</p>
  
  <p>I am using extjs 4 in MVC model. Here is my code:</p>
  
  <p>my init inside the viewport:</p>
  
  <pre><code>init: function() {
      this.control({
          'viewport &gt; combobox': {
              select: this.onChangeStacker
          }
      });
  },
  
  // method with pseudocode of what I want to do
  onChangeStacker: function(){
  
      selected =  getSelection;
  
  
     switch selected
  
      case == stk1
  
           load stk1
  
      case == stk2 
  
           load stkd
  }
  });
  </code></pre>