title: this.lookupReference('referenceName') returning null?
body: <p>I created a login page, for my project, I made it work, but the problem is, I can't call the reference of the login form from my login controller, what could possible go wrong? please see below for my code:</p>
  
  <p>This is my Login.Js which is under classic -> src -> view -> login -> Login.js:</p>
  
  <pre><code>Ext.define('DevToolsTraining.view.login.Login', {
  extend: 'Ext.window.Window',
   xtype: 'loginView',
  
   requires: [
     'DevToolsTraining.view.login.LoginController',
     'Ext.form.Panel'
   ],
  
   viewModel:{
       type: 'login',
       data:{
           username: ''
       }
   },
  controller: 'login',
  
  title: 'Enter Username',
  frame: true,
  width: 320,
  bodyPadding: 10,
  closable: false,
  autoShow: true,
  
  layout: 'form',
  
  items: [
      {
          xtype: 'login',
          reference: 'loginForm',  //i'm trying to call this 
          defaultType: 'textfield',
          bind: '{Login}',
          items: [{
              id:'txtUsername',
              allowBlank: false,
              fieldLabel: 'Username',
              name: 'Username',
              emptyText: 'enter username here...',
              bind: '{username}'
          }],
          buttons: [{
                  text: 'Proceed&gt;&gt;',
                  formBind: true,
                  handler: 'onProceedClick'
              }]
      }
  ]
  
  });
  </code></pre>
  
  <p>And here is my controller under app -> view -> login -> LoginController.js</p>
  
  <pre><code>Ext.define('DevToolsTraining.view.login.LoginController', {
  extend: 'Ext.app.ViewController',
  alias: 'controller.login',
  
  
  onProceedClick: function () {
      var form = this.lookupReference('loginForm'); //this returns null it's like it can't see the "loginForm" reference
      var username = Ext.getCmp('txtUsername').getValue(); //i got the value of the textbox here but i don't like this coz what if I have more textFields
  
      if (username != '')
      {
          Ext.Ajax.request({
                  url: '/api/Users/Post',
                  method: 'POST',
                  params: username,
                  scope: this,
                  success: function (form, response) {
  
                      localStorage.setItem("username", username);
  
                      this.getView().destroy();
  
                      Ext.create({
                          xtype: 'app-main'
                      });
                  },
                  failure: function(form, response){
                      Ext.MessageBox.alert("Test");
                  }
              })
      }
      else {
          Ext.MessageBox.alert("Error", "Please enter username to view contacts");
      }
  },
  /**
   * Called when the view is created
   */
  init: function () {
  
  }
  });
  </code></pre>