Sencha Touch Listeners in a Static Class

NotificationManager.js

Ext.define('SenchaSandbox.util.NotificationManager', {

    alternateClassName: 'NotificationManager',
    requires: ['Ext.MessageBox'],
    mixins: ['Ext.mixin.Observable'],

    singleton: true,

    constructor: function(config) {
        this.initConfig(config);

        // Works correctly for a singleton class
        this.addListener({
            initEvent: function() {
                Ext.Msg.alert('Test Event', 'The initEvent added via the constructor has been fired.');
            }
        });
    },

    // Does not seem to work for a singleton
    listeners: {
        configEvent: function() {
            Ext.Msg.alert('Read Event', 'The configEvent added by the listeners config has been fired.');
        }
    }
});

Ext.define('SenchaSandbox.view.Main', {
    extend: 'Ext.tab.Panel',
    xtype: 'main',
    requires: ['Ext.TitleBar', 'Ext.Button'],
    config: {
        tabBarPosition: 'bottom',

        items: [{
            title: 'Welcome',
            iconCls: 'home',

            styleHtmlContent: true,
            scrollable: true,

            items: [
                {
                    docked: 'top',
                    xtype: 'titlebar',
                    title: 'Single Class Event Tests'
            	}, 
                {
                    xtype: 'button',
                    text: 'Fire initEvent',
                    
                    listeners: {
                    	tap: function () {
                    		NotificationManager.fireEvent('initEvent');
                    
                		}
                	}
            	},
                {
                    xtype: 'button',
                    text: 'Fire configEvent',
                    
                    listeners: {
                    	tap: function () {
                    		NotificationManager.fireEvent('configEvent');
                    
                		}
                	}
            	}
            ],

            html: "Hello World"
        }]
    }
});

Ext.application({
    name: 'SenchaSandbox',

    requires: ['Ext.MessageBox', 'SenchaSandbox.util.NotificationManager'],

    views: ['SenchaSandbox.view.Main'],

    launch: function() {
        // Initialize the main view
        Ext.Viewport.add(Ext.create('SenchaSandbox.view.Main'));
    }
});