Ext.form.RadioGroup的赋值问题

需要在页面中加入以下代码，可以加到任意处

Ext.override(Ext.form.BasicForm,{  
    findField : function(id){          
        var field = this.items.get(id);          
        if(!field){  
            this.items.each(function(f){  
                if(f.isXType('radiogroup')||f.isXType('checkboxgroup')){  
                    f.items.each(function(c){  
                        if(c.isFormField && (c.dataIndex == id || c.id == id || c.getName() == id)){  
                            field = c;  
                            return false;  
                        }  
                    });  
                }  
                                  
                if(f.isFormField && (f.dataIndex == id || f.id == id || f.getName() == id)){  
                    field = f;  
                    return false;  
                }  
            });  
        }  
        return field || null;  
    }   
});
然后赋值
form.findById('iscluster').setValue('true');