title: Ext.Viewport.add is not a function In Ext js
body: <p>I am very new to Ext js . I am trying to implement Grid in application in that once user will click on data new msg window will open with current data and user can edit that and this will saved in model. I am using Classic toolkit</p>
  
  <p>I tried like this:</p>
  
  <pre><code>Ext.define('MyApp.view.main.MainController', {
      extend: 'Ext.app.ViewController',
  
      alias: 'controller.main',
      require:['Ext.plugin.Viewport'],
  
      itemtap: function (view,index,item,record) {
         Ext.Viewport.add({
         xtype:'formpanel',
         title:'update',
         width:300,
         centered: true,
         modal: true,
         viewModel : {
                          data: {
                              employee: record
                          }
                      },
         items: [{
  
                          xtype: 'textfield',
                          name: 'firstname',
                          label: 'First Name',
                          bind: '{employee.name}'
  
                      }, {
                          xtype: 'toolbar',
                          docked: 'bottom',
                          items: ['-&gt;', {
                              xtype: 'button',
                              text: 'Submit',
                              iconCls: 'x-fa fa-check',
                              handler: function() {
                                  this.up('formpanel').destroy();
                              }
                          }, {
                              xtype: 'button',
                              text: 'Cancel', 
                              iconCls: 'x-fa fa-close',
                              handler: function() {
                                  this.up('formpanel').destroy();
                              }
                  }]
             }]
       })
  </code></pre>
  
  <p>and In my other file i am calling this function like</p>
  
  <pre><code>listeners: {
          select: 'itemtap'
      }
  </code></pre>
  
  <p>But i am getting error like Ext.Viewport.add is not a function</p>
  
  <p>Kindly suggest me how can i make it possible .</p>
  
  <p>Any suggestions are welcome .</p>