title: including selectOneMenu in datatable
body: <p>i have created datatable with four selectOneMenu in it 
  whenever i change the first selectOneMenu values of second selectOneMenu need to be populated on the same row and again on the selection of second selectOneMenu third needs to populate
  i had done this by passing row number value to each selectOneMenu (with intention which particular selectOneMenu user must has clicked on) but whenever i pass the value with f:param i am getting null value on the controller but same can be printed with outputText on datatable</p>
  
  <p>please guide</p>
  
  <pre><code>&lt;t:dataTable id="insertTaskDataTable" border="1"
                  value="#{insertTask.taskList}" var="taskInfo" rowIndexVar="row"  
                  iterationStatusVar="it"&gt;
                  &lt;t:column&gt;
                  &lt;h:inputHidden  id="id" value="#{row}"/&gt;
                  &lt;/t:column&gt;                 
              &lt;t:column&gt;
                  &lt;f:facet name="header"&gt;#{bundle['GROUP_HEADER']}&lt;/f:facet&gt;
                  &lt;h:selectOneMenu id="taskGroup" value="#{taskInfo.groupList.comboValue}" onchange="document.getElementById('addTask:filterButton').click();"&gt;
                      &lt;f:param  name="idTaskGroup" value="#{row}"/&gt;
                      &lt;t:outputText  name="id" value="#{row}"/&gt;
                       &lt;f:selectItems value="#{taskInfo.groupList.comboValues}" /&gt;
                  &lt;/h:selectOneMenu&gt;
  
              &lt;/t:column&gt;
              &lt;t:column&gt;
                  &lt;f:facet  name="header"&gt;#{bundle['ACTIVITY_HEADER']}&lt;/f:facet&gt;
                  &lt;h:selectOneMenu id="taskActivity" value="#{taskInfo.activityList.comboValue}"&gt;
                  &lt;f:ajax  render="taskSubActivity" listener="#{insertTask.handleActivityChange}"&gt;&lt;/f:ajax&gt;   
                  &lt;f:selectItems value="#{taskInfo.activityList.comboValues}" /&gt;
                  &lt;/h:selectOneMenu&gt;
  
              &lt;/t:column&gt;
              &lt;t:column&gt;
                  &lt;f:facet name="header"&gt;#{bundle['SUBACTIVITY_HEADER']}&lt;/f:facet&gt;
                  &lt;h:selectOneMenu id="taskSubActivity" value="#{taskInfo.subActivityList.comboValue}"&gt;
                      &lt;f:selectItems value="#{taskInfo.subActivityList.comboValues}" /&gt;
                  &lt;/h:selectOneMenu&gt;
  
              &lt;/t:column&gt;
              &lt;t:column&gt;
                  &lt;f:facet name="header"&gt;#{bundle['COMPLEXTIY_HEADER']}&lt;/f:facet&gt;
                  &lt;h:selectOneMenu id="taskComplexity" value="#{taskInfo.complexityList.comboValue}"&gt;
                      &lt;f:selectItems value="#{taskInfo.complexityList.comboValues}" /&gt;
                  &lt;/h:selectOneMenu&gt;
  
              &lt;/t:column&gt;
  
              &lt;t:column&gt;
                  &lt;f:facet name="header"&gt;#{bundle['BENCHMARK_EFFORT_HEADER']}&lt;/f:facet&gt;
                  &lt;t:inputText  value="#{taskInfo.benchMarkHrs}" /&gt;
                  &lt;t:outputLabel value="hrs"/&gt;
                  &lt;t:inputText  value="#{taskInfo.benchMarkMin}" /&gt;
                  &lt;t:outputLabel value="min"/&gt;
  
              &lt;/t:column&gt;
  
              &lt;t:column&gt;
                  &lt;f:facet name="header"&gt;#{bundle['DESCRIPTION_HEADER']}&lt;/f:facet&gt;
                  &lt;t:inputText value="#{taskInfo.taskdescription}" /&gt;
              &lt;/t:column&gt;
  
  
          &lt;/t:dataTable&gt;
      &lt;/t:div&gt;
  
              &lt;a4j:commandButton id="filterButton" style="visibility:hidden;display:none" action="#{insertTask.handleGroupChange}" render="insertTaskDataTable" /&gt;
  </code></pre>