Change input based on combo value

问题

I know this question exists somewhere else in SO but either the solutions are old (and JSF seems to have improved a lot) or I cannot make the solution work.

As simple as it sounds, I would like to replace the text of an input element based on the value of a combo box. I would like to use Ajax, and would like this to work even if there is only one element in the combo (it doesn't matter if by default the selection of the combo is empty).

<h:selectOneMenu id="fnamecombo" valueChangeListener="#{namesController.setForename(fnamecombo)}">
    <c:forEach items="#{namesController.myForenames}" var="myforename">
        <f:selectItem itemValue="#{myforename}" itemLabel="#{myforename}" />
    </c:forEach>
    <f:ajax render="fnameinput"  />
</h:selectOneMenu>

<h:inputText value="#{namesController.forename}" id="fnameinput" />

This doesn't work. So first of all, I have no idea how to call the setForename method. If I use valueChangeListener="#{namesController.setForename('xxxxx')}" it works, but only the 1st time and iff there are more than one element in the combo, since otherwise the event does not seem to be fired.

What is the easy fix?

EDIT

Ok, so I have made progress. It was easier than I expected:

<h:selectOneMenu id="fnamecombo" value="#{namesController.forename}">
    <c:forEach items="#{namesController.myForenames}" var="myforename">
        <f:selectItem itemValue="#{myforename}" itemLabel="#{myforename}" />
    </c:forEach>
    <f:ajax render="fnameinput"  />
</h:selectOneMenu>

<h:inputText value="#{namesController.forename}" id="fnameinput" />

This seems to work on a selectItem that I create by hand, but not on the one that is printing with the foreach loop. So this is the rendered code, where I obtained 'john' from the loop and I manually created 'example':

<select id="myForm:fnamecombo" name="myForm:fnamecombo" size="1" onchange="mojarra.ab(this,event,'valueChange',0,'myForm:fnameinput')">
    <option value="example">example</option>
    <option value="john">john</option>
</select>

It works with 'example' but not with 'john'.

回答1:

Finally I got the answer.

<h:selectOneMenu id="fnamecombo" value="#{namesController.forename}">
    <f:selectItems value="#{namesController.myForenames}" />
    <f:ajax render="fnameinput"  />
</h:selectOneMenu>

<h:inputText value="#{namesController.forename}" id="fnameinput" />

No need for forEach as mentioned by Alexandre Lavoie.

This answer by Luiggi Mendoza gave me the hint to find it out. The reason my input was not updated by the values in the f:selectItems and it was in the ones that I introduced manually is the scope of the managed bean. I realised that the input was actually being updated in any case, but when coming from the f:selectItems the input was updated with null. Why? Because the scope of namesController was @RequestScoped and not @ViewScoped. Changing this solves the problem.

来源：https://stackoverflow.com/questions/40182423/change-input-based-on-combo-value

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