JSF - f:ajax execute does not update the backing property of bean

I have two components, one commandButton and a selectOneListbox.

I need to update the value of the backing property binded to selectOneListBox after I click on the commandButton.

Both components are inside the same <h:form>. The backing Bean is a Named/SessionScoped bean.

Here is the part of my page where the components are defined:

Button:

    <h:commandButton formnovalidate="formnovalidate" title="Select Variable" 
                     type="button" styleClass="button_green close_window" 
                     tabindex="2" id="btnSelectVar" value="Confirm">
         <f:ajax execute="lstVarSelected" event="click" 
                 listener="#{systemOptionsControl.updateText}" onevent="updateParent"/>
    </h:commandButton>


SelectOneListBox: (selectedVariable is a String and variables is a List of String)


    <h:selectOneListbox id="lstVarSelected" name="lstVarSelected" 
                        tabindex="1" value="#{systemOptionsControl.selectedVariable}" >
        <f:selectItems value="#{systemOptionsControl.variables}"/>
    </h:selectOneListbox>

After I click on button, I need to get the backing propert of the oneListBox, but JSF isnt calling the set method on backing bean. Then, when I try to get the value on my updateText method, i got a NullPointerException.

I've trie a lot of solutions and none worked, anyone can give any ideas?

Here is the xhtml:

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" >
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ui="http://java.sun.com/jsf/facelets"
      xmlns:h="http://java.sun.com/jsf/html"
      xmlns:escriba="http://java.sun.com/jsf/composite/components/escriba"
      xmlns:f="http://java.sun.com/jsf/core" lang="pt-br" class="no-js">
    <body>
        <h:head>
            <h:outputScript name="jsf.js" library="javax.faces"/>
            <script language="javascript">
                function callParentButton(data) {
                    //Verifica o status da execução do ajax. 
                    var status = data.status;
                    //alert(status);
                    switch(status)
                    {
                        case 'begin':
                            break; 
                        case 'complete':
                            //Gets the name of parent button
                            var a = #{systemOptionsControl.idBtnAtualizarTextAreas}; 
                            //Calls the click.
                            var btn = document.getElementById(a.valueOf().name);
                            btn.click();
                            break;
                        } 
                    }
            </script>
        </h:head>
        <h:form prependId="false" id="frmVariables">
            <section class="box_padrao">
                <header id="box_padrao_header">
                    <h1>System Options</h1>            
                    <div id="actions_menu">
                        <h:commandButton type="button" title="Select Variable" styleClass="button_green" tabindex="2" 
                                         id="btnConfirmar" value="Confirm">
                            <f:ajax execute="lstVariables" event="click" listener="systemOptionsControl.updateText" onevent="callParentButton"/>
                        </h:commandButton>
                        <button type="button" title="Cancel" class="button_red close_window" tabindex="3" id="btnCancelar" name="btnCancel">Cancel</button>
                    </div> 
                </header>
                <div class="box_padrao_content">
                    <div class="grid_100">
                        <h2 class="legend">» Variables List </h2>   
                        <fieldset class="fieldset">
                            <div class="grid_100">
                                <h:selectOneListbox id="lstVariables" name="lstVariables" tabindex="1" value="#{systemOptionsControl.selectedVariable}" >
                                    <f:selectItems value="#{systemOptionsControl.variables}"/>
                                </h:selectOneListbox>
                            </div>
                        </fieldset>
                    </div>      
                </div>
            </section>
        </h:form> 
    </body>
</html>

And here is the Bean:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package br.com.xxx.rodrigoms.control;


import java.util.ArrayList;
import java.util.List;
import javax.annotation.PostConstruct;
import javax.enterprise.context.SessionScoped;
import javax.inject.Named;

/**
 *
 * @author rodrigos
 */
@Named
@SessionScoped
public class SystemOptionsControl{    

    private String selectedVariable;

    @PostConstruct
    public void initialize() {
        //non-matter code
    }

    //<editor-fold desc="GETS/SETS">
    public String getIdBtnAtualizarTextAreas(){
        return "btnUpdateTextAreas";
    }

    public String getSelectedVariable() {
        return selectedVariable;
    }

    public void setSelectedVariable(String selectedVariable) {
        this.selectedVariable = selectedVariable;
    }

    public List<String> getVariables() {
        List<String> ret = new ArrayList<>();
        //just simulating
        ret.add("1");
        ret.add("2");
        ret.add("3");
        ret.add("4");
        return ret;
    }

    //</editor-fold>

    //<editor-fold desc="Other methods">
    public void updateText(){
        //I get the NullPointerException right on next line
        String variavelAInserir = "<".concat(this.selectedVariable).concat(">");,

        /*
        code do other suffs
        */
    }
    //</editor-fold>

    }

Sorry about any language errors, was need change some names because its a "job" for a company.

Solution

Well, I solved using the binding property.

After I bound a inputTextArea in my bean. I was able to get the selectedValue in my listener method.

The reason for the execute not "really" execute the set method before the execution of the listener i didnt discover yet.

Anyway, thank you two guys for the great help :) This was my first time asking in stackoverflow and you two were very prestative :)

Thanks!