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

please guide

```
<t:dataTable id="insertTaskDataTable" border="1"
                value="#{insertTask.taskList}" var="taskInfo" rowIndexVar="row"  
                iterationStatusVar="it">
                <t:column>
                <h:inputHidden  id="id" value="#{row}"/>
                </t:column>                 
            <t:column>
                <f:facet name="header">#{bundle['GROUP_HEADER']}</f:facet>
                <h:selectOneMenu id="taskGroup" value="#{taskInfo.groupList.comboValue}" onchange="document.getElementById('addTask:filterButton').click();">
                    <f:param  name="idTaskGroup" value="#{row}"/>
                    <t:outputText  name="id" value="#{row}"/>
                     <f:selectItems value="#{taskInfo.groupList.comboValues}" />
                </h:selectOneMenu>

            </t:column>
            <t:column>
                <f:facet  name="header">#{bundle['ACTIVITY_HEADER']}</f:facet>
                <h:selectOneMenu id="taskActivity" value="#{taskInfo.activityList.comboValue}">
                <f:ajax  render="taskSubActivity" listener="#{insertTask.handleActivityChange}"></f:ajax>   
                <f:selectItems value="#{taskInfo.activityList.comboValues}" />
                </h:selectOneMenu>

            </t:column>
            <t:column>
                <f:facet name="header">#{bundle['SUBACTIVITY_HEADER']}</f:facet>
                <h:selectOneMenu id="taskSubActivity" value="#{taskInfo.subActivityList.comboValue}">
                    <f:selectItems value="#{taskInfo.subActivityList.comboValues}" />
                </h:selectOneMenu>

            </t:column>
            <t:column>
                <f:facet name="header">#{bundle['COMPLEXTIY_HEADER']}</f:facet>
                <h:selectOneMenu id="taskComplexity" value="#{taskInfo.complexityList.comboValue}">
                    <f:selectItems value="#{taskInfo.complexityList.comboValues}" />
                </h:selectOneMenu>

            </t:column>

            <t:column>
                <f:facet name="header">#{bundle['BENCHMARK_EFFORT_HEADER']}</f:facet>
                <t:inputText  value="#{taskInfo.benchMarkHrs}" />
                <t:outputLabel value="hrs"/>
                <t:inputText  value="#{taskInfo.benchMarkMin}" />
                <t:outputLabel value="min"/>

            </t:column>

            <t:column>
                <f:facet name="header">#{bundle['DESCRIPTION_HEADER']}</f:facet>
                <t:inputText value="#{taskInfo.taskdescription}" />
            </t:column>

        </t:dataTable>
    </t:div>

            <a4j:commandButton id="filterButton" style="visibility:hidden;display:none" action="#{insertTask.handleGroupChange}" render="insertTaskDataTable" />

```