JSF: the binding value of selectOneMenu never get set

I have a selectOneMenu look like this

<h:form>
  <h:selectOneMenu value="#{CreateAds.selectedOwnerId}">
      <f:selectItem itemLabel="Select a Owner" itemValue=""/>
      <f:selectItems value="#{CreateAds.availableOwner}" />
  </h:selectOneMenu>
</h:form>

Here is my CreateAds ViewSc开发者_Python百科oped bean

@ViewScoped
public class CreateAds extends View {        

private List<SelectItem> availableOwner = null;

private String selectedOwnerId = null;

public CreateAds() {
}

@PostConstruct
public void init(){
    availableOwner = new ArrayList<SelectItem>();
    List<User> users = scholarEJB.findSponsorAndAdmin();
    for(User u : users){
        availableOwner.add(new SelectItem(u.getId().toString(), u.getFname() + " " + u.getLname()));
    }
} 
//getters and setters
}

The list display correctly, but when value selectedOwnerId attribute never got set. Its value is null. Here is the html my code generated

<select size="1" name="j_idt50:j_idt51">
  <option value="">Select a Owner</option>
  <option value="19102">Harry Pham</option>
  <option value="27101">Thomas Chang</option>
  <option value="27562">Hao Shen Lin</option>
</select>

You need a command button/link in the same form as the dropdown.