Make multiple dependent / cascading selectOneMenu dropdown lists in JSF

问题

I am trying to make 4 dependent menus.

When the user chooses an item from the first menu, the second menu will show dependent data and when the user chooses item from the second one , the third one will show dependent data and so on.

The user will see items on the first menu only and the other ones will be blank. If he chooses an item on the first menu the second one will show data but the third and the fourth will remain blank, and so on. The user must eventually choose entries from all the 4 menus.

<h:selectOneMenu id=\"first\" value=\"#{nodes.selectState\"}>
    <f:selectItems value=\"#{nodes.stateList}\"/>
    <f:ajax render=\"second\">
</h:selectOneMenu>
<h:selectOneMenu id=\"second\" value=\"#{nodes.selectCity\"}>
    <f:selectItems value=\"#{nodes.cityList}\"/>
    <f:ajax render=\"third\">
</h:selectOneMenu>
<h:selectOneMenu id=\"third\" value=\"#{nodes.selectRegion\"}>
    <f:selectItems value=\"#{nodes.regionList}\"/>
    <f:ajax render=\"fourth\">
</h:selectOneMenu>
<h:selectOneMenu id=\"fourth\" value=\"#{nodes.selectStation\"}>
    <f:selectItems value=\"#{nodes.stationList}\"/>
</h:selectOneMenu>

nodes Java Class

private String selectState; //+setters, getters
private String selectCity; //+setters, getters
private String selectRegion; //+setters, getters
private String selectStation; //+setters, getters
private List<SelectItem> stateList; //+setters, getters
private List<SelectItem> cityList; //+setters, getters
private List<SelectItem> regionList; //+setters, getters
private List<SelectItem> stationList; //+setters, getters

public getStateList(){
    stateList= new ArrayList<SelectItem>();
    stateList.add(new SelectItem(\"A\"));
}

public getCityList(){
    CityList= new ArrayList<SelectItem>();
    if(selectState.equals(\"A\")){
        CityList.add(new SelectItem(\"B\"));
    }
}

public getRegionList(){
    RegionList= new ArrayList<SelectItem>();
    if(selectCity.equals(\"B\")){
        RegionList.add(new SelectItem(\"C\"));
   }
}

public getStationList(){
    StationList= new ArrayList<SelectItem>();
    if(selectRegion.equals(\"C\")){
        StationList.add(new SelectItem(\"D\"));
    }
}

it\'s only working at the first 2 menus the other 2 menus get null values

回答1:

Put the bean in the view scope and get rid of any business logic in getter methods.

The bean must be placed in the view scope so that all previous selections and new available items are remembered, otherwise things will fail if e.g. rendered attribute depends on a condition which was only set in a previous request, or if JSF needs to validate the selected item against list of available items.

The getter methods should not contain any business logic as they will also be invoked during a.o. validations phase. You should use <f:ajax listener> to perform business logic based on a change. You should in the listener method also explicitly clear out selected values of child dropdowns. You can use <f:ajax render> to update the contents of child dropdowns.

Thus, so:

<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>

with

@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.
}

回答2:

There is a typo error in your code. For third menu you have given id name as "first" instead of "third". May be its because of that problem.

回答3:

Try this, it may help you

By using the --Select City-- , --Select Region--, --Select Station-- to avoid the null pointer Exception.

    public getStateList(){
    stateList= new ArrayList<SelectItem>();
    stateList.add(new SelectItem("A"));
    }

    public getCityList(){
    CityList= new ArrayList<SelectItem>();
    if(selectState.equals("A"))
    {
      CityList.add(new SelectItem("B"));
    }
    else
    {
      CityList.add(new SelectItem("--Select City--"));
      selectCity = "--Select City--";
    }

    public getRegionList(){
    RegionList= new ArrayList<SelectItem>();
    if(selectCity.equals("B"))
    {
      RegionList.add(new SelectItem("C"));
    }
    else
    {
      RegionList.add(new SelectItem("--Select Region--"));
      selectRegion = "--Select Region--";
    }
    }

    public getStationList(){
    StationList= new ArrayList<SelectItem>();
    if(selectRegion.equals("C"))
    {
       StationList.add(new SelectItem("D"));
    }
    else
    {
      StationList.add(new SelectItem("Select Station"));
      selectStation = "--Select Station--";
    }
    }