primefaces : show message growl if there isn´t a selected item, else open dialog

I want to check the following: I have a dataTable, but selected a row and I click the edit button, then you must leave a message, otherwise open a popup so that the user can change the value

my button is:

 <p:commandButton value="#{bundle.Edit}" id="editBotonFormula" icon="ui-icon-pencil" update=":growl" oncomplete="handleSubmit(args,'OprEditarFormulaDialog');" actionListener="#{oprFormulaMedicaController.validarSeleccionado}"/>

My Managed bean method is:

public void validarSeleccionado(){

    if (selected != null) {

        System.out.println(" hay dato seleeccionado en formulaMedica" + selected);
   //open popup to edit Dialogvar.Show;


    }
    else {
        System.out.println("No hay dato seleccionado " + selected);
        //Show open error message (growl) and not open popup JsfUtil.addErrorMessage(ResourceBundle.getBundle("/Bundle").getString("NoHayFilaSeleccionada"));
    }
}

My question is : How can I open the dialog (popup)if the row is selected ?????

thanks

Try the following

 if (selected != null) {
     System.out.println(" hay dato seleeccionado en formulaMedica" + selected);
     RequestContext context = RequestContext.getCurrentInstance();
     context.execute("PF('OprEditarFormulaDialog').show();");
 }

by using the Primefaces function PF to locate your dialog. Prerequisite: You have a p:dialog with widgetvar="OprEditarFormulaDialog".