Hello,
I am a newbie on Jboss seam, and I have a problem trying to create fields on forms dynamically, I have seen several examples but it does not work.
I get the following exception when I try to render the page: 

javax.faces.FacesException: javax.el.ELException: /crearActividad.xhtml @23,64 binding="#{crearActividad.containerComponent}": Error reading 'containerComponent' on type com.tresw.reservas.session.CrearActividad_$$_javassist_1

My Action class is as follows:

package com.tresw.reservas.session;

import java.util.LinkedList;
import java.util.List;

import org.jboss.seam.annotations.Begin;
import org.jboss.seam.annotations.Factory;
import org.jboss.seam.annotations.Name;
import org.jboss.seam.annotations.In;
import org.jboss.seam.annotations.Logger;
import org.jboss.seam.annotations.Out;
import org.jboss.seam.log.Log;
import org.jboss.seam.international.StatusMessages;
import org.richfaces.component.html.HtmlComboBox;
import org.hibernate.validator.Length;

import com.tresw.reservas.entity.Tipocampo;

import javax.faces.component.UIColumn;
import javax.faces.component.UISelectItems;
import javax.faces.component.html.HtmlInputText;
import javax.faces.component.html.HtmlOutputText;
import javax.faces.component.html.HtmlPanelGrid;
import javax.faces.model.SelectItem;

@Name("crearActividad")
public class CrearActividad
{
    @Logger private Log log;

    @In StatusMessages statusMessages;

    private String value;
    
    @In(required = false, create = true)
    @Out
    private HtmlPanelGrid containerComponent;

    public void crearActividad()
    {
        // implement your business logic here
        log.info("crearActividad.crearActividad() action called with: #{crearActividad.value}");
        statusMessages.add("crearActividad #{crearActividad.value}");
    }

    public HtmlPanelGrid getContainerComponent() {
                return containerComponent;
        }

        public void setContainerComponent(HtmlPanelGrid containerComponent) {
                this.containerComponent = containerComponent;
        }

        @Length(max = 10)
    public String getValue()
    {
        return value;
    }
  
    public void setValue(String value)
    {
        this.value = value;
    }
    
    public List<SelectItem> getSelectItem()
    {
        List<Tipocampo> campos = new TipocampoList().getResultList();
        List<SelectItem> result = new LinkedList<SelectItem>();
        for(Tipocampo campo : campos)
        {
                SelectItem item = new SelectItem(campo.getId().intValue(),campo.getTipo());
                result.add(item);
        }
        return result;  
    }           
    
    public List<Tipocampo> getItems()
    {
        List<Tipocampo> campos = new TipocampoList().getResultList();
        return campos;  
    }           
    
    public void addComponents() {
        //clean previous component
        containerComponent.getChildren().clear();
        
        int nodes = Integer.parseInt(value);
        //dynamically add Child Components to Container Component
        for (int i=0;i<nodes; i++) 
        {
            UIColumn col = new UIColumn();
            HtmlOutputText ot = new HtmlOutputText();
            ot.setValue("Nombre del campo" + ": ");
            col.getChildren().add(ot);
            HtmlInputText it = new HtmlInputText();
            it.setValue("");
            it.setId("nombre"+i);
            col.getChildren().add(it);

            UIColumn col2 = new UIColumn();
            HtmlOutputText ot2 = new HtmlOutputText();
            ot2.setValue("Tipo del campo" + ": ");
            col2.getChildren().add(ot2);
            HtmlComboBox combo = new  HtmlComboBox();
            UISelectItems items = new UISelectItems();
            items.setValue(items);
            combo.getChildren().add(items);
            col2.getChildren().add(combo);

            
            if (containerComponent == null) {
                containerComponent = new HtmlPanelGrid();
            }
            containerComponent.getChildren().add(col);
            containerComponent.getChildren().add(col2);
        }

    }
   
    @Factory("containerComponent")
        @Begin(join = true)
        public void start()
    {
                containerComponent = new HtmlPanelGrid();
        }
}

And my page is as follows:

<!DOCTYPE composition PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
    xmlns:s="http://jboss.com/products/seam/taglib"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:rich="http://richfaces.org/rich"
    xmlns:a="http://richfaces.org/a4j"
    template="layout/template.xhtml">

<ui:define name="body">

    <h:form id="crearActividadForm">

        <rich:panel>
            <f:facet name="header">crearActividad</f:facet>
                                 <s:decorate id="valueField" template="layout/edit.xhtml">
                        <ui:define name="label">Value</ui:define>
                        <h:inputText id="value" required="true" value="#{crearActividad.value}"/>
                    </s:decorate>
           
                        <h:panelGrid binding="#{crearActividad.containerComponent}">              
                         <h:commandButton value="Anadir campos" action="#{crearActividad.addComponents}" partialSubmit="true"/>
                        </h:panelGrid>
           
            
                <div style="clear:both"/>          
       

        </rich:panel>

        <div class="actionButtons">
            <h:commandButton id="crearActividad" value="crearActividad"
                    action="#{crearActividad.crearActividad}"/>
        </div>

    </h:form>

</ui:define>

</ui:composition>

Can anybody help me?

Or give me an example on how generating the form dynamically?

thanks in advance