When i press tab button ,control will go to collapse icon of the panel,but it wont go to TextField of the panel..How to do it..

var somePanel = new sap.ui.commons.Panel({

             id:"somePanel",

             text:"Panel",

             showCollapseIcon:true

        });

somePanel.addDelegate({

            onAfterRendering: function() {

                $("#somePanel").attr("tabindex", -1);

            }

        });

but I need Collapse Icon also