Display combo box when checkbox is checked - Extjs

Question

I have setup a checkbox and a combobox and I am trying to set up a functionality - when a user checks the checkbox the combobox has to appear. I am new to extjs and I am having issues setting up the function for this functionality.

Ext.onReady(function() {

var tests = [
    ['Test1'],
    ['Test3'],
    ['Test2']
];
Ext.define('Testfile.model.Test', {
    extend: 'Ext.data.Model',
    fields: ['test']
});
var testsStore = new Ext.data.Store({
    model: 'Testfile.model.Test',
    proxy: {
        type: 'memory',
        reader: {
            type: 'array'
        }
    },
    data: tests
});
var form = Ext.create('Ext.form.Panel', {
    renderTo: document.body,
    bodyPadding: 10,
    width: 550,
    style: 'margin:16px',
    height: 300,
    title: 'Testing example',
    items: [{

          xtype: 'checkbox',
          name: 'system',
          boxLabel: 'Production (PACTV)',
          iputValue: 'production',

        listeners: {
            check: function (checkbox, isChecked) {
                    var sample = Ext.getCmp('secondComboID');
                }

        }
    }, {
        xtype: 'combobox'
        fieldLabel: 'Select Test',
        id: 'secondComboID',
        store: testsStore,
        valueField: 'id',
        displayField: 'test',
        typeAhead: true,
        forceSelection: true,
        allowBlank: false,
        editable: true,
        triggerAction: 'all',
        lastQuery: ''
    }]
});
Ext.getBody().add(me.form);

})

Can someone please suggest a fix to the script?

Solution

I would use the change event: http://docs.sencha.com/extjs/4.2.2/#!/api/Ext.form.field.Checkbox-event-change

listeners: {
    change: function(checkbox, newValue, oldValue, eOpts) {
        var combo = checkbox.up('form').down('combobox');
        if (newValue) {
            combo.show();
        } else {
            combo.hide();
        }
    }
}

Also, please notice the use of the hierarchy navigation methods up() and down(). Using these (or other related methods) to find the component is much more preferable than using hard-coded component Ids.

Here's a working example of your code: https://fiddle.sencha.com/#fiddle/ua