这是我的托管 bean 中的代码:-
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core">
<h:head>
<title>Facelet Title</title>
</h:head>
<h:body>
<center>
<h:form>
<h2> <u>Select Fruit(s). </u> </h2>
<!-- Value Change Listener is entirely superflous. You can make a full blown project without requiring the need to ever use this...This is
just for demo purpose..-->
<h:selectManyMenu onchange="document.forms[0].submit();" style="height: 200px;font-size: 1.5em;width: 200px;" >
<f:selectItems value="#{actionValueLisBean.fruitsList}" var="fruit" itemLabel="#{fruit}" itemValue="#{fruit}"/>
<f:valueChangeListener type="beans.ActionValueLisBean"/>
</h:selectManyMenu>
<h3> Your previous selection is :<h:outputText value="#{actionValueLisBean.prevSel}"/></h3>
<h3>Your current selection is :<h:outputText value="#{actionValueLisBean.currSel}"/></h3>
</h:form>
</center>
</h:body>
</html>
这是我的豆子:-
package beans;
import com.sun.jmx.remote.internal.ArrayQueue;
import java.util.List;
import javax.enterprise.context.RequestScoped;
import javax.faces.bean.ManagedBean;
import javax.faces.event.AbortProcessingException;
import javax.faces.event.ValueChangeEvent;
import javax.faces.event.ValueChangeListener;
@ManagedBean
@RequestScoped
public class ActionValueLisBean implements ValueChangeListener {
private List<String> fruitsList;
private String currSel;
private String prevSel;
public String getCurrSel() {
return currSel;
}
public void setCurrSel(String currSel) {
this.currSel = currSel;
}
public String getPrevSel() {
return prevSel;
}
public void setPrevSel(String prevSel) {
this.prevSel = prevSel;
}
public List<String> getFruitsList() {
return fruitsList;
}
public void setFruitsList(List<String> fruitsList) {
this.fruitsList = fruitsList;
}
public ActionValueLisBean() {
fruitsList = new ArrayQueue<String>(5);
fruitsList.add("Apple");
fruitsList.add("Mango");
fruitsList.add("Banana");
fruitsList.add("Peach");
fruitsList.add("Plum");
}
@Override
public void processValueChange(ValueChangeEvent event) throws AbortProcessingException {
if(event.getOldValue() != null)
prevSel = event.getOldValue().toString();
if(event.getNewValue() != null)
currSel = "abc";
}
}
然后我有 prevSel 和 currSel 绑定到h:outputText
. 但是,即使 processValueChange 被正确触发并且System.out.println(event.getNewValue());
工作正常,该值也没有得到。我也尝试设置不同的bean范围,但没有用。我知道 ValueChangeListener 完全没用。我仍然想知道它是如何工作的。
提前致谢 :)