primefaces context menu do not update to dialog box input - jsf-2

Question

I have see this problem.Please see my jsf page.
<h:form id="companyList">
<p:contextMenu for="companiesDB" style="height:53px;">
<p:menuitem value=" edit" update="panelGrid" icon="ui-icon-pencil" oncomplete="editCompany.show()" />
<p:menuitem value=" delete" update="panelGrid" icon="ui-icon-closethick" onclick="editCompany.show()" />
</p:contextMenu>
<p:dataTable id="companiesDB" var="companies"
value="#{companyController.companyList}" rowKey="#{companies.pkId}"
selection="#{companyController.selectedCompany}"
selectionMode="single" paginator="true"
paginatorTemplate="{CurrentPageReport} {FirstPageLink} {PreviousPageLink} {PageLinks} {NextPageLink} {LastPageLink} {RowsPerPageDropdown}"
rows="20" >
<p:column headerText="name">
#{companies.companyName}
</p:column>
<p:column headerText="desc">
#{companies.description}
</p:column>
</p:dataTable>
<p:dialog header="edit mode" widgetVar="editCompany"
modal="true" height="160" width="390"
id="dialog" resizable="false">
<p:panelGrid cellpadding="10" id="panelGrid" >
<p:row>
<p:column width="300">
<h:outputText value="name:" style="float:left;" />
</p:column>
<p:column>
<p:inputText value="#{companyController.selectedCompany.companyName}"/>
</p:column>
</p:row>
<p:row>
<p:column>
<h:outputText value="desc:" style="float:right;" />
</p:column>
<p:column>
<p:inputText
value="#{companyController.selectedCompany.description}" />
</p:column>
</p:row>
</p:panelGrid>
<br />
<br />
<p:commandButton value="save" icon="ui-icon-check"
style="float:right; margin-right:25px;" update="companiesDB"
oncomplete="addCompany.hide();"
action="#{companyController.insertCompany()}">
</p:commandButton>
</p:dialog>
</h:form>
And console error was :
/company.xhtml #46,91 value="#{companyController.selectedCompany.companyName}": Target Unreachable, 'selectedCompany' returned null

Answer 1

try renaming your dialog id to mydialog (just to be on a safe side)
and update your menu item entry as following (notice the update="mydialog"):
<p:menuitem value="edit" update="mydialog" icon="ui-icon-pencil" oncomplete="editCompany.show()" />
also , make sure the edit button will be enabled only after a selection in table was made... otherwise you will get the null pointer...
you can achieve it with something like
<p:menuitem value="edit" disabled=#{companyController.selectedCompany eq null}.....
and add two p:ajax in your table
<p:dataTable.......>
<p:ajax event="rowSelect" update="contextMenuID" />
<p:ajax event="rowUnselect" update="contextMenuID" />
last thing : add id=contextMenuID to your context menu