title: When using setHandler in ExtJS button, the handler function was executed right away
body: <p>I added a button to a panel. When you click the button, a popup window will show up. I tried to update the content of the popup using setHandler. But whenever setHandler was called, the handler function was executed right away. Here is the example code:</p>
  
  <pre><code>
      me.panels[i].getDockedItems()[0].setHandler(Popup({html: tiphtml}), this);
      ...
      Popup = function(cfg) {
        cfg = Ext.apply({
          height: 100, 
          width: 200,
          layout: 'fit'
        }, cfg);
  
        Ext.create('Ext.window.Window', {
            title: cfg.title,
            height: cfg.height,
            width: cfg.width,
            layout: cfg.layout,
            html: cfg.html 
        }).show();
      }
  </code></pre>