JSF 关于JSF 添加 ajax 支持(a4j:support event="onchange" reRender=""),导致绑定值为空

当我们在Jsf页面用了以下代码时：

会导致<a4j:support evnet="onchange"/>在绑定stbAddBean.users.state属性时 会导致 users=null。

<h:column><h:inputText value="#{stbAddBean.users.firstName}" id="firstName" required="true"

requiredMessage="用户名不能为空"><rich:ajaxValidator event="onblur" /></h:inputText></h:column><h:column><h:outputText style="color:red" value="* "/><rich:message for="firstName" style="color:red" /></h:column><h:column><h:selectOneMenu value="#{stbAddBean.users.state}" id = "state" style="width: 150"  requiredMessage="所在省不能为空"><f:selectItem itemLabel="All" itemValue=""/><f:selectItems value="#{stbAddBean.allProvince}"/><a4j:support  actionListener="#{stbAddBean.allCityByProvince}" event="onchange" reRender="city" /></h:selectOneMenu></h:column>

解决如下 在以下代码上加上 ajaxSingle="true"就OK

<a4j:support ajaxSingle="true" event="onchange" reRender="city"/>