I have an ExtJS window that contains checkboxgroups in it and a button to get the selected values.

I have two isseus with it. This is the code:
Ext.create('widget.window', 
    {
        title  : 'Select which scenario to run',
        draggable: true,
        modal: true,
        header : 
        {
            titlePosition : 2,
            titleAlign    : 'center'
        },
        closable    : true,
        closeAction : 'hide',
        width       : 400,
        height      : 350,
        x           : contentPanel.getX() + 50,
        y           : contentPanel.getY() + 50,
        layout: {
        type: 'hbox',
        align: 'stretch'
        },
        items: 
        [
            {
                xtype: 'panel',
                title: 'If success',
                itemId : 'success',
                autoScroll:true,
                flex: 1,
                items:
                [{
                    xtype: 'checkboxgroup',
                    columns: 1,
                    vertical:true,
                    items: 
                    [
                        { boxLabel: 'Item 1', name: 'rb', inputValue: '1' },
                        { boxLabel: 'Item 2', name: 'rb', inputValue: '2' },
                        { boxLabel: 'Item 3', name: 'rb', inputValue: '3' },
                        { boxLabel: 'Item 4', name: 'rb', inputValue: '4' },
                        { boxLabel: 'Item 2', name: 'rb', inputValue: '2' },
                        { boxLabel: 'Item 3', name: 'rb', inputValue: '3' },
                        { boxLabel: 'Item 4', name: 'rb', inputValue: '4' },
                        { boxLabel: 'Item 5', name: 'rb', inputValue: '5' },
                        { boxLabel: 'Item 6', name: 'rb', inputValue: '6' }
                    ]
                }]
            },
            {
                xtype: 'panel',
                title: 'If failure',
                id: 'failure',
                autoScroll:true,
                flex: 1,
                items:
                [{
                    xtype: 'checkboxgroup',
                    columns: 1,
                    vertical:true,
                    items: 
                    [
                        { boxLabel: 'Item 1', name: 'rb', inputValue: '1' },
                        { boxLabel: 'Item 2', name: 'rb', inputValue: '2' },
                        { boxLabel: 'Item 3', name: 'rb', inputValue: '3' },
                        { boxLabel: 'Item 4', name: 'rb', inputValue: '4' },
                        { boxLabel: 'Item 2', name: 'rb', inputValue: '2' },
                        { boxLabel: 'Item 3', name: 'rb', inputValue: '3' },
                        { boxLabel: 'Item 4', name: 'rb', inputValue: '4' },
                        { boxLabel: 'Item 5', name: 'rb', inputValue: '5' },
                        { boxLabel: 'Item 6', name: 'rb', inputValue: '6' }
                    ]
                }]
            }
        ],
        buttons:
        [{
            text    : 'Save',
            itemId  : 'if_save',
            icon    : '../images/save.png',
            ui      : 'default',
            handler : function()
            {
                var cb_f = Ext.getCmp('failure').getValue()
                alert(JSON.stringify(cb_f));
            }
        }]
    }).show(); 
In button handler I want to get the selected items from checkboxes. 
I have tried this.getComponent('success').getValue(), Ext.getCmp('failure').getValue(), but firebug keeps saying that they are undefined.
So, How can I get the values on 'Save' click?
Thanks
 
     
     
     
    