Extjs - Getting value from Window to Panel and Panel to Window

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Javascript

ExtJS

I have created a panel and placed into the windows. when I click OK button in Window I can get the value of the panel.

var FormPanel = Ext.create('Ext.form.Panel', {
                   id: 'formpanel',
                   frame: true,
                   renderTo: Ext.getBody(),

                   xtype: 'radiogroup',
                   fieldLabel: 'Show',
                   layout: 'vbox',
                   items:

                        {
                       xtype: 'radiogroup',
                       layout: 'hbox',
                       items: [{
                           xtype: 'radiofield',
                           fieldLabel: 'PAN Number*',
                           margin: "20 0 0 0",
                           name: 'rb',
                           inputValue: '1',
                           checked: false,
                           listeners: {
                               change: function(cb, nv, ov) {
                                   if (nv) {
                                       Ext.getCmp('AttachData').disable();
                                       Ext.getCmp('PanData').enable();
                                   }
                               }
                           }
                       }, {
                           xtype: 'splitter'
                       }, {
                           xtype: 'textfield',
                           emptyText: 'Enter Owner\'s PAN...',
                           margin: "20 0 0 0",
                           id: 'PanData',
                           disabled: false
                       }, ]
                   },
               });

               var winPanDetails = Ext.create('Ext.window.Window', {
                   height: 250,
                   width: 400,
                   id:'winPanDetails',
                   layout: 'fit',
                   modal: true,
                   closable: true,
                   title: 'Document Attach',
                   items: [FormPanel],
                   constrain: true,
                   renderTo: Ext.getBody(),
                   buttons: [{
                       width: 50,
                       text: 'OK',
                       id: 'btnOk',
                       handler: function() {

                           if (Ext.getCmp('PanData').value == "") {
                               Ext.Msg.alert("Tax Benefit Declaration", "Please Pan Number");
                               return;
                           } else {
                               this.up('window').close();

                           }
                       }
                   }]
               }).show();

I need to insert this window to my main panel...

Ext.create('Ext.form.Panel', {
       renderTo: 'container',
       title: 'Main Panel',
       defaultType: 'textfield',
       id: 'mainPanel',
       bodyPadding: 10,
       width: 780,
       defaults: {
           labelWidth: 100
       },
       items: [
       {
        //Some more fields
         button:[{
                       width: 50,
                       text: 'OK',
                       id: 'btnOk',
                       handler: function() {
                         //My Window
                    }
               }]
       },

but after inserting I couldn't get the value of the window from my main panel. I tried many logics, Please help me with the logic
I cant get the value of Ext.getCmp('PanData').value outside the window

if (Ext.getCmp('PanData').value == "") {
                    Ext.Msg.alert("Tax Benefit Declaration", "Please enter  pan number");
                    return;
                }