如何检索激活p：contextMenu

Question

我的环境是：Primefaces 5.1; jdk 7.0.40; JSF 2.0（Mojarra 2.03-FCS）; Tomcat 7.0。 我构建了一个p：selectOneListbox和p：contextMenu：一切正常。问题是：如果尚未执行任何选择，如何检索列表中的哪个项目触发了contextMenu（右键单击时正确显示）？

    <h:form id="recipeFilesForm">
    <h:outputText value="Recipe files" style="position:relative;left:40px;font-size:0.9em;" />
    <p:selectOneListbox id="recipeFileList"   value="#{RecipeFormMngr0.selecteduserFileIndex}" 
        style="width:190px;font-size:0.7em;text-align:left;position:relative;left:-24px">
        <f:selectItems value="#{RecipeFormMngr0.recipeFileNamesItems}" var="u" itemLabel="#{u.label}" itemValue="#{u.value}">
        </f:selectItems>
        <p:ajax event="click"  listener="#{RecipeFormMngr0.selecteduserFileIndexSelected}"  />
    </p:selectOneListbox>
    <p:contextMenu for="recipeFileList" style="font-size:0.7em;">
        <p:menuitem value="Show"   actionListener="#{RecipeFormMngr0.showRecipeContent}" ajax="true" process=":loginForm0_1:userSettingTab:recipeFilesForm" />
        <p:menuitem value="Delete" actionListener="#{RecipeFormMngr0.deleteRecipeFile}" ajax="true" process=":loginForm0_1:userSettingTab:recipeFilesForm" />
        <p:menuitem value="Edit"   actionListener="#{RecipeFormMngr0.editRecipeContent}" ajax="true" process=":loginForm0_1:userSettingTab:recipeFilesForm" />
    </p:contextMenu>
</h:form>