HTML and CSS Reference
In-Depth Information
public void findCapital(ValueChangeEvent event) {
System.out.println("Old selected value is: " + event.getOldValue());
System.out.println("New selected value is: " + event.getNewValue());
String selectedCountryName = (String) event.getNewValue();
if ("USA".equals(selectedCountryName)) {
capital = "Washington";
} else if ("Egypt".equals(selectedCountryName)) {
capital = "Cairo";
} else if ("Denmark".equals(selectedCountryName)) {
capital = "Copenhagen";
As you notice in the bolded lines, the value change listener method returns void and has ValueChangeEvent as
a parameter. Using getOldValue() and getNewValue() methods of ValueChangeEvent , you can get the old and the
new values of the ValueHolder (or EditableValueHolder ) components. In our example, we get the new value which
represents the new country selection, then get the suitable capital for the selected country, and finally set the result in
the capital attribute in order to be displayed by the page, as shown in Listing 4-11.
Instead of firing the value change event by changing the value of the ValueHolder (or EditableValueHolder )
component and click on a CommandButton or a CommandLink . You can fire the value change event when the value of
the ValueHolder (or EditableValueHolder ) component changes by submitting the form when the component's value
changes. Listing 4-13 shows how to apply this behavior by removing the CommandButton and submitting the form on
value change.
Listing 4-13. Executing the Value Change Listener by Submitting the Form on SelectOneMenu's Value Change
<h:outputLabel for="countries" value="Select a country: "/>
<h:selectOneMenu id="countries" value="#{}"
onchange="submit();" >
<f:selectItem itemLabel="---" itemValue="---"/>
<f:selectItem itemLabel="United States" itemValue="USA"/>
<f:selectItem itemLabel="Egypt" itemValue="Egypt"/>
<f:selectItem itemLabel="Denmark" itemValue="Denmark"/>
</h:selectOneMenu> <br/>
<h:outputText value="Capital of #{} is #{}"
rendered="#{ ne null}"/>
Adding to using the default value change listener, you can write your own custom value change listener. This
can be done by creating a custom value change listener class that implements ValueChangeListener interface.
Listing 4-14 shows CountryValueChangeListener , which utilizes ValueChangeListener and implements
processValueChange() , which gets the new selected country and then finds its capital and finally sets the result in the
capital attribute of the Country managed bean.
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