Sencha Touch 1.1: Focusing TextArea after show method
===

I am currently creating a web-based Mobile App using Phonegap 1.6.0 and Sencha Touch 1.1. The app consists of a number of panels through which the user can click. 
Some of these panels have textfields or textareas in them. Upon entering the panel, we want these to automatically be focused. This seems to work with textfields but not with textareas.

I have a Panel with the following component:

    xtype: 'textareafield',
    cls: 'jasbackblock',
    id: 'addreactiontextarea',
    height: '100%',
    grow: true,
    listeners: {
        afterrender: function(cmp) {
        console.log('Component rendered.');
        cmp.fieldEl.dom.focus();
    }

Whenever I first open the panel, it automatically focuses, which is good. However, when I leave the panel and then return to it, I cannot think of a good way to do this with events.
I have previously tried the show listener in the panel:

    listeners: {
        show: function(cmp) {
            Ext.get('addreactiontextarea').fieldEl.dom.focus();
        }
    }

This gives me the following error:

    Uncaught TypeError: Cannot read property 'fieldEl' of null 

It seems that I cannot access the element during the show event. Is there any other event that I could use which fires every time the panel is loaded and allows me to access the textarea?

If it is any help, this is the method we call to switch from one panel to another:

    function switchScreen(from, to, newArgs) {
        /* Save screen information. */
        if (from != -1)
            historyStack.push([from, screenArgs]);
            
        if (currentPage > 2) {
            if (to != 3)
                main.getComponent(3).hide();
            app.getComponent(currentPage - 3).hide();
        }
        else
            main.getComponent(currentPage).hide();

        screenArgs = newArgs;

        if (to > 2) {
            main.setActiveItem(3);
            app.setActiveItem(to - 3);

            /* setActiveItem does not fire a screen's show event if it has been
             * shown before. Since we want the code in the screen's show listener to
             * be executed every time we switch to the screen, we call show manually
             * just to fire the event. */
            main.getComponent(3).show();
            app.getComponent(to - 3).show();
        }
        else {
            main.setActiveItem(to);
            main.getComponent(to).show();
        }

        if (to == 0 || to == 1)
            adMode = to;
        else
            adMode = -1;

        currentPage = to;
    }

Thanks in advance.