How to retrieve and show list of values in listbox and text corresponding to list item in textarea - jsf

Question

I need to use a list box to show some values from database and do further processing when a single value from the list is selected.
At the PrimeFaces showcase site the example loads fixed (static) data into the listbox and there is one PrimeFaces command for each list item. How do I show items in a list box dynamically, when I may not know the number of items beforehand?
I also need to show some text corresponding to the item selected in list, in a textarea. Do I have to use an event listener for this purpose? I would like to leave the text area blank at the beginning. Only when a value is selected in the list box, then I want to use a bean to retrieve and store data using that textarea. Is this possible? How do I implement this?

Answer 1

How do I show items in a list box dynamically, when I may not know the number of items beforehand?
Use <f:selectItems> which you bind to a List<T> property. Basic example, assuming you're using EJB/JPA to interact with DB:
private Item selectedItem; // +getter+setter
private List<Item> availableItems; // +getter
#EJB
private ItemService service;
#PostConstruct
public void init() {
availableItems = service.list();
}
with
<p:selectOneListbox value="#{bean.selectedItem}" converter="itemConverter">
<f:selectItems value="#{bean.availableItems}" var="item"
itemValue="#{item}" itemLabel="#{item.someLabel}" />
</p:selectOneListbox>
The itemConverter should implement javax.faces.convert.Converter and convert from the Item object to its unique string representation (usually its DB identifier) in getAsString() and convert the other way round getAsObject().
I also need to show some text corresponding to the item selected in list, in a textarea. Do I have to use an event listener for this purpose?
Just put a <p:ajax> (the PrimeFaces equivalent of standard JSF <f:ajax>) in the listbox which updates the textarea. E.g.
<p:selectOneListbox value="#{bean.selectedItem}" converter="itemConverter">
<f:selectItems value="#{bean.availableItems}" var="item"
itemValue="#{item}" itemLabel="#{item.someLabel}" />
<p:ajax update="textarea" />
</p:selectOneListbox>
<p:inputTextarea id="textarea" value="#{bean.selectedItem.someText}" />
It'll be invoked when you select an item.
See also:
Our h:selectOneMenu wiki page - same applies to PrimeFaces p:selectOneListbox

Answer 2

Yes, for demonstration purposes most of the examples are loaded with static data. But if you look at the same example on PF showcase, the second listbox code is as follows:
<h:outputText value="Scrollbar: " />
<p:selectOneListbox id="scroll" value="#{autoCompleteBean.selectedPlayer1}"
converter="player" style="height:100px">
<f:selectItems value="#{autoCompleteBean.players}"
var="player" itemLabel="#{player.name}" itemValue="#{player}" />
</p:selectOneListbox>
and f:selectItems value attribute can point to a collection, an array, a map or a SelectItem instance. So coming to the above example players could be any list that is being populated using a database in the managed bean.
But if the instance is not a SelectItem, the labels are obtained by calling a toString on each object and finally the selected itemValue is set to the selectedPlayer1 attribute but you can also see that there is a converter in between so the incoming itemValue string is converted back to a player object and then set to selectedPlayer1.
And if you want to display the selected item in a text area, you can do something like this:
<h:outputText value="Scrollbar: " />
<p:selectOneListbox id="scroll" value="#{autoCompleteBean.selectedPlayer1}"
converter="player" style="height:100px">
<f:selectItems value="#{autoCompleteBean.players}"
var="player" itemLabel="#{player.name}" itemValue="#{player}" />
<p:ajax update="displayArea"/>
</p:selectOneListbox>
<p:inputTextarea id="displayArea" value="#{autoCompleteBean.selectedPlayer1}" />
Here the inputTextarea is updated using ajax with the value selected by the user.