在JSF中创建多个依赖/级联selectOneMenu下拉列表

必须将bean放在视图范围中,以便记住所有先前的选择和新的可用项,否则,如果例如,则会失败.呈现属性取决于仅在先前请求中设置的条件,或者JSF是否需要针对可用项列表验证所选项.

getter方法不应包含任何业务逻辑,因为它们也将在a.o期间调用.验证阶段.你应该使用< f：ajax listener>基于变化执行业务逻辑.您应该在侦听器方法中明确清除子下拉列表的选定值.你可以使用< f：ajax render>更新子下拉列表的内容.

因此,所以：

<h:selectOneMenu id="state" value="#{nodes.selectedState}">
    <f:selectItem itemValue="#{null}" itemLabel="-- select --" />
    <f:selectItems value="#{nodes.availableStates}" />
    <f:ajax listener="#{nodes.changeState}" render="city region station" />
</h:selectOneMenu>
<h:selectOneMenu id="city" value="#{nodes.selectedCity}">
    <f:selectItem itemValue="#{null}" itemLabel="-- select --" />
    <f:selectItems value="#{nodes.availableCities}" />
    <f:ajax listener="#{nodes.changeCity}" render="region station" />
</h:selectOneMenu>
<h:selectOneMenu id="region" value="#{nodes.selectedRegion}">
    <f:selectItem itemValue="#{null}" itemLabel="-- select --" />
    <f:selectItems value="#{nodes.availableRegions}" />
    <f:ajax listener="#{nodes.changeRegion}" render="station" />
</h:selectOneMenu>
<h:selectOneMenu id="station" value="#{nodes.selectedStation}">
    <f:selectItem itemValue="#{null}" itemLabel="-- select --" />
    <f:selectItems value="#{nodes.availableStations}" />
</h:selectOneMenu>

同

@ManagedBean
@ViewScoped
public class Nodes {

    private String selectedState; // getter+setter
    private String selectedCity; // getter+setter
    private String selectedRegion; // getter+setter
    private String selectedStation; // getter+setter
    private List<SelectItem> availableStates; // getter (no setter necessary!)
    private List<SelectItem> availableCities; // getter (no setter necessary!)
    private List<SelectItem> availableRegions; // getter (no setter necessary!)
    private List<SelectItem> availableStations; // getter (no setter necessary!)

    @EJB
    private SomeService someService;

    @PostConstruct
    public void init() {
        availableStates = someService.listStates();
    }

    public void changeState(AjaxBehaviorEvent event) {
        availableCities = someService.listCities(selectedState);
        selectedCity = selectedRegion = selectedStation = null;
        availableRegions = availableStations = null;
    }

    public void changeCity(AjaxBehaviorEvent event) {
        availableRegions = someService.listRegions(selectedCity);
        selectedRegion = selectedStation = null;
        availableStations = null;
    }

    public void changeRegion(AjaxBehaviorEvent event) {
        availableStations = someService.listStations(selectedRegion);
        selectedStation = null;
    }

    // Generate necessary getters+setters here. You should not change them.
}

也可以看看：

> How to choose the right bean scope?
> Best way to add a “nothing selected” option to a selectOneMenu in JSF
> How to populate options of h:selectOneMenu from database?
> When to use valueChangeListener or f:ajax listener?
> Why JSF calls getters multiple times