Hello! How can i add an item to an existent window? I tried win.add() but it does not seem to work. Why? This is my piece of code:

function combo_service(winTitle,desc,input_param) {

        /* parametri */
        param=input_param.split(","); /* della forma: param[0]="doc1:text", quindi da splittare di nuovo */

   /* cosi' non la creo più volte */
   win;

   if (!win)
    var win = new Ext.Window({
         //title:Ext.get('page-title').dom.innerHTML
        renderTo:Ext.getBody()
        ,iconCls:'icon-bulb'
        ,width:420
        ,height:240
        ,title:winTitle
        ,border:false
        ,layout:'fit'
        ,items:[{
            // form as the only item in window
             xtype:'form'
            ,labelWidth:60
                ,html:desc
            ,frame:true
            ,items:[{
                // textfield
                 fieldLabel:desc
                ,xtype:'textfield'
                ,anchor:'-18'
                }]
        }]
        });

win.add({
            // form as the only item in window
             xtype:'form'
            ,labelWidth:60
                ,html:desc
            ,frame:true
            ,items:[{
                // textfield
                 fieldLabel:desc
                ,xtype:'textfield'
                ,anchor:'-18'
                }]});

    win.show();


}; 

What's wrong with my code? Thank you very much.