While you modify element or add widget, you must return app function listBoxClick( eventInfo ) { var app = UiApp.getActiveApplication(); Logger.log( "listBoxClick: " + eventInfo.parameter.searchListbox ); var text = app.getElementById( "text" ); text.setText( eventInfo.parameter.searchListbox ); var title = app.getElementById( "title" ); title.setText( eventInfo.parameter.searchListbox ); return app; }