Ajax-chained selectManyListBoxes

[maciekpazur]

Hello.

I do realize that the problem of ajax-chained selects has been discussed a number of times.
But I tried to follow all the advice and didn't manage to make my application work.

I am trying to implement searching UI for my application (issue management system).
User can select some projects in selectManyListBox.

<a4j:region id="projectsPanel">

     <h:selectManyListbox value="#{searchIssue.selectedProjects}" size="5">
          <s:selectItems value="#{allProjects.resultList}" var="proj"
               label="#{proj.name}" />
          <s:convertEntity />
          <a4j:support event="onchange"
               action="#{searchIssue.projectsSelected()}" reRender="modulesPanel" />
     </h:selectManyListbox>

</a4j:region>

Then relevant modules should appear in another selectManyListbox.

<a4j:outputPanel id="modulesPanel">
     <h:selectManyListbox value="#{searchIssue.selectedModules}" size="5">
          <s:selectItems value="#{searchIssue.availableModules}" var="module"
               label="#{module.name}" />
          <s:convertEntity />
     </h:selectManyListbox>
</a4j:outputPanel>

The view is supported with a backing bean SearchIssuesAction:

@Scope(CONVERSATION)
@Name("searchIssue")
@Stateful
public class SearchIssuesAction implements SearchIssues {

@In(create = true, value = "#{allProjects.resultList}")
@SuppressWarnings(value = { "unused" })
private List<Project> allProjects;

private List<Project> selectedProjects;
private List<Module> selectedModules;
private List<Module> availableModules;

(...)
     
public void projectsSelected() {
     List<Module> available = new LinkedList<Module>();
     if (selectedProjects != null)
          for (Project project : selectedProjects) {
               available.addAll(project.getModules());
          }
     availableModules = available;
}

(...getters and setter for selectedProjects, selectedModules, availableModules...)

I run into a number of problems

The only way to display the page, without getting an error

Expected a child component type of UISelectItem/UISelectItems for component type javax.faces.SelectMany(j_id57). Found null.

is to render the modules select only if availableModules list size is greater than 0.
I want this select to be empty unless any projects with modules have been selected.

If I make the above-mentioned workaround, the modules appear on the list, but
  when I submit the form it turns out that selectedModules is null.

I would greatly appreciate any help.

[joblini]

Hi, have you tried adding the noSelectionLabel attribute to the selectItems tag?  This attribute adds a selectItem representing no choice (null).

[maciekpazur]

Thanks, that helped a bit:)

No I can render the modules select at any time (no projects have to be selected).

But

• If I select the some items including noSelectionLabel I get

Exception during request processing:
Caused by javax.servlet.ServletException with message: ""

(...)

Caused by java.lang.NullPointerException with message: ""

javax.faces.component.UISelectMany.matchValue(UISelectMany.java:508)
javax.faces.component.UISelectMany.validateValue(UISelectMany.java:466)
javax.faces.component.UIInput.validate(UIInput.java:875)
javax.faces.component.UIInput.executeValidate(UIInput.java:1072)
(...)

• If I select any other items I get a validation error

• The application works only if I don't select anything in the modules select (then the selectedModules list is empty)

Have you got any ideas?

[maciekpazur]

OK. I added

<begin-conversation join="true"/> 

to the appropriate page.xml file.
Now I don't get the validation error.

My last problem is to detect that the noSelectionLabel has been chosen.
When noSelectionLabel is chosen in a selectOne null is returned as select value. I haven't got the slightest idea why it is different when I use selectMany.

Greetings.