Having issue with calling a function from a buttonhandler inside a tabPanel

[gendaful]

Back Ground : I am working on an MVC application using sencha touch 2. I am working on a page which has two tabs. Inside the first tab, I have a button inside a title bar.
Issue : I am not able to call anyother function from the button handler. I think, there is an issue with the scope of the calling function.

Here is my code.

Ext.define('WUPOC.view.WUHomePage',
{
extend: 'Ext.TabPanel',
requires:['Ext.TitleBar','Ext.dataview.List','Ext.data.proxy.JsonP'],
alias: 'widget.wuHomePageView',

config: {
fullscreen: true,
defaults: {
styleHtmlContent: true
},

items:
[
{ // First Tab
title: 'Home',
iconCls: 'home',
items: [
{
xtype: 'titlebar',
title: 'Hello',
docked: 'top',
items: [ {
xtype: 'button',
text: 'LogOut',
ui: 'action',
itemId: 'newButton',
align: 'right',
handler : function(btn)
{
console.log('LogOut is tapped'); // This is printed
this.up.onNewButtonTap(); // Throws error
}
}],
}],
},
// Second Tab

{
title: 'Contact',
iconCls: 'user',
html: 'Contact Screen'
}
]
},

onNewButtonTap: function ()
{
console.log('newNoteCommand');
},
});
I am getting the error as below.

Uncaught TypeError: Object function (selector)
{
var result = this.parent;
if (selector)
{
for (; result; result = result.parent)
{ if (Ext.ComponentQuery.is(result, selector))
{ return result;
} } }
return result; } has no method 'onNewButtonTap'

I think there is an issue with setting the scope of a button. Kindly help.
Thank you

[gendaful]

There was an issue with the scope.

I set xtype to the main container and then using that as a selector, i was able to call the function like below
this.up('myXType').onNewButtonTap();

Thanks