Problem with Navigation Controller in Android

First, my English is very poor :)

I am using "navigation controller". I have various .js. My idea is: 1- app.js call Principal.js. 2- Principal call Materias.js 3- Materias.js call Unidades.js 4- Unidades.js call ... 5- ....

1 and 2 work fine. 3 don't work fine when a row is clicked.

Error message: Title: Runtime error Location: [20,16] ui/Materias.js Message: Uncaught TypeError: Cannot call method 'open' of undefined Source: navController.open(new Unidades(this.navController));

Location: [20,16] ui/Materias.js is the line: navController.open(new Unidades(this.navController));

I need Help :) simply i want navigate between various windows.

Code:

app.js

var NavigationController = require('NavigationController').NavigationController,
Principal = require('ui/Principal').Principal;
//create NavigationController which will drive our simple application
var controller = new NavigationController();
//open initial window
controller.open(new Principal(this.controller));

Materias.js

exports.Materias = function(navController){
var win = Titanium.UI.createWindow({title:'Materias'});
// array de materias
var tbl_materias = [
{title:'Algoritmos y Complejidad'},
{title:'Programación Orientada a Objetos'},
{title:'Base de Datos'}];
var tabla = Titanium.UI.createTableView({data:tbl_materias});
win.add(tabla);
var Unidades = require('Unidades').Unidades;
tabla.addEventListener('click',function(){navController.open(new Unidades(this.navController));
});
return win;
}

Principal.js

exports.Principal = function(navController) {
// this sets the background color of the master UIView (when there are no windows/tab groups on it)
Titanium.UI.setBackgroundColor('#000');
var win = Titanium.UI.createWindow({title:'Acceso', height:'auto', layout:'vertical'});
var usuarioLabel = Titanium.UI.createLabel({
text:'Usuario',
textAlign:'center',
width:'auto'
});
 
win.add(usuarioLabel);
var usuarioText = Titanium.UI.createTextField({
width:200, height:30 })
win.add(usuarioText);
var passLabel = Titanium.UI.createLabel({
text:'Contraseña',
textAlign:'center',
width:'auto'
});
win.add(passLabel);
var passText = Titanium.UI.createTextField({
width:200,
height:30
})
win.add(passText);
var ingresarBtn = Titanium.UI.createButton({
title:'Ingresar'
})
win.add(ingresarBtn);
var Materias = require('Materias').Materias;
ingresarBtn.addEventListener('click', function() {navController.open(new Materias(this.navController));});
return win;
}

Unidades.js

exports.Unidades = function(navController){
var win = Titanium.UI.createWindow({
title:'datos Unidad'});
// array de unidades
var tbl_unidades = [{title:'Unidad 1'}, {title:'Unidad 2'}, {title:'Unidad 3'}];
var tabla = Titanium.UI.createTableView({
data:tbl_unidades
});
win.add(tabla);
var Materias = require('Materias').Materias;
var ingresarBtn = Titanium.UI.createButton({title:'Ingresar'})
return win;
}

NavigationController.js

exports.NavigationController = function() {
    this.windowStack = [];
};
 
exports.NavigationController.prototype.open = function(/*Ti.UI.Window*/windowToOpen) {
    //add the window to the stack of windows managed by the controller
    this.windowStack.push(windowToOpen);
 
    //grab a copy of the current nav controller for use in the callback
    var that = this;
    windowToOpen.addEventListener('close', function() {
        that.windowStack.pop();
    });
 
    //hack - setting this property ensures the window is "heavyweight" (associated with an Android activity)
    windowToOpen.navBarHidden = windowToOpen.navBarHidden || false;
 
    //This is the first window
    if(this.windowStack.length === 1) {
        if(Ti.Platform.osname === 'android') {
            windowToOpen.exitOnClose = true;
            windowToOpen.open();
        } else {
            this.navGroup = Ti.UI.iPhone.createNavigationGroup({
                window : windowToOpen
            });
            var containerWindow = Ti.UI.createWindow();
            containerWindow.add(this.navGroup);
            containerWindow.open();
        }
    }
    //All subsequent windows
    else {
        if(Ti.Platform.osname === 'android') {
            windowToOpen.open();
        } else {
            this.navGroup.open(windowToOpen);
        }
    }
};
 
//go back to the initial window of the NavigationController
exports.NavigationController.prototype.home = function() {
    //store a copy of all the current windows on the stack
    var windows = this.windowStack.concat([]);
    for(var i = 1, l = windows.length; i < l; i++) {
        (this.navGroup) ? this.navGroup.close(windows[i]) : windows[i].close();
    }
    this.windowStack = [this.windowStack[0]]; //reset stack
};