Dynamically load items for radiogroup

[floraoma2000-extjs]

Hi all,
I need help for my problem (ExtJs 4) . I want to load some items (data from my database) for my radiogroup dynamically.

First of all I tried to solve the problem - step by step - by loading the items into an array like this.

var radiogroup = [
   { boxLabel: 'Item 11', name: 'rb', inputValue: '1' },
   { boxLabel: 'Item 21', name: 'rb', inputValue: '2' },
   { boxLabel: 'Item 31', name: 'rb', inputValue: '3' }
];

Ext.create('Ext.form.Panel', {
    title: 'RadioGroup Example',
    renderTo: Ext.getBody(),
    items:[{
        xtype: 'radiogroup',
        fieldLabel: 'RadioGroup',
        items: radiogroup
    }]
});    

This code works fine !

The next step like this works fine too.
I load the items via a store.

Ext.onReady(function () {
var store_fest = Ext.create('Ext.data.Store', {
    fields: ["boxLabel", "name", "inputValue"],   
    data:{'groupitems':[
        { boxLabel: 'Item 1x', name: 'rb', inputValue: '1' },
        { boxLabel: 'Item 2x', name: 'rb', inputValue: '2' },
        { boxLabel: 'Item 3x', name: 'rb', inputValue: '3' }
    ]},
    proxy: {
        type: 'memory',
        reader: {
            type: 'json',
            root: 'groupitems'
        }
    }    
});

var radioArray = [];
for (var i = 0; i < store_fest.data.length; i++) {  
    radioArray.push(store_fest.data.items[i].data); 
}

Ext.create('Ext.form.Panel', {
    title: 'RadioGroup Example',
    renderTo: Ext.getBody(),
    items:[{
        xtype: 'radiogroup',
        fieldLabel: 'RadioGroup',
        items: radioArray
    }]
});    
});

The response data-format of a database select is JSON. So now I want to load the items reading a json store .This doesn't work. Here my code

Ext.onReady(function () {
var store_json = Ext.create('Ext.data.JsonStore', {
    storeId: 'radio',
    fields: ['boxLabel', 'name', 'inputValue'],  
    proxy: {
        type: 'ajax',
        url: 'items.json',   
        reader: {type: 'json', root: 'groupitems',totalProperty: 'total'},
        baseParams: { 
            operation:'showall' 
        },
    },
});

var itemsInGroup = store_json.load({
    callback: function(records, operation, success) {
        itemsInGroup = [];
            console.log(store_json.data.length);
            for (var i = 0; i < store_json.data.length; i++) {  
                itemsInGroup.push(store_json.data.items[i].data); 
            }
            console.log(itemsInGroup);
    }
});
var itemsInGroup = [];

Ext.create('Ext.form.Panel', {    
    title: 'RadioGroup Example',
    renderTo: Ext.getBody(),
    items:[{
        xtype: 'radiogroup',
        fieldLabel: 'Radio',
        items: itemsInGroup 
    }]
});    
});

This log to the console (console.log(itemsInGroup) shows the right array.
Here is my items.json

{
    "groupitems": [ 
   { boxLabel: 'Item 1', name: 'rb', inputValue: '1' },
   { boxLabel: 'Item 2', name: 'rb', inputValue: '2' },
   { boxLabel: 'Item 3', name: 'rb', inputValue: '3' }
    ]
}

There are no data shown in my Panel.

Please help me. Thanks a lot in advance.