function checkbox(){
                var checkboxItem = [];
                var chs = ['A','B','C','D'];
                    for(var i = 0; i < chs.length; i++){
                        var cls = "width-"+chs[i]+"-box";
                        var checkbox = new Ext.form.Checkbox({
                            id:chs[i]+"id",
                            boxLabel:chs[i],
                            listeners:{
                                render:function(el){
                                    el.getEl().parent().addClass(cls);
                                }
                            }
                        });
                        checkboxItem.push(checkbox);
                    }
                    return checkboxItem;
            }