Ext.define('MyApp.view.main.Main', {
  extend: 'Ext.container.Container',
  .....
  do Stuff
  .....
    tbar: [{
    text: 'Button',
    handler: function(){
      var mask = Ext.create('MyApp.view.main.EntryForm');
      mask.show(this);

Ext.define('MyApp.view.main.EntryForm',{
  extend: 'Ext.Widget',
  ....
  generate my items for the form
  ....