javascript - EL expression inside p:commandButton onclick does not update/re-render on ajax request?

Question

The onclick attribute of my commandButton has some EL dependent Javascript inside. To be more specific, here is that piece of code:

<p:commandButton
    onclick="javascript: if('#{userBean.user.friendList.size() gt 0}' == 'true') deleteFriendsConfirmDialog.show(); else friendsAlreadyDeletedErrorDialog.show();"
    value="Delete all friends?" />

deleteFriendsConfirmDialog clears the list of friends and updates the @form. The list of friends, commandButton and the dialogs are all in that form.

So I click the button, confirmation dialog comes up (because the length of friends' list is gt 0), I confirm and the list is emptied, the view is updated. However, when I click the Delete all friends? button once more, the confirmation dialog comes up again. Since the length of the list is now 0, I instead expect the error dialog to show.

That, I guess, is because the Javascript written inside onclick is not updated (although the button is in the form).

Edit: Changing #{userBean.user.friendList.size() gt 0} to #{not empty userBean.user.friendList} doesn't work neither.

How come? What's wrong here?

Any help appreciated. :)

Answer 1

Indeed. PrimeFaces (and standard JSF) does not re-evaluate the EL in on* attributes on a per-request basis. It only happens on a per-view basis. RichFaces however does that in <a4j:xxx> components.

You need to solve the problem differently. I suggest to use the visible attribute of the <p:dialog> instead.

<h:form>
    ...
    <p:commandButton value="Delete all friends?" update=":deleteDialogs" />
</h:form>
...
<h:panelGroup id="deleteDialogs">
    <p:dialog id="deleteFriendsConfirmDialog" visible="#{facesContext.postback and not empty userBean.user.friendList}">
        ...
    </p:dialog>
    <p:dialog id="friendsAlreadyDeletedErrorDialog" visible="#{facesContext.postback and empty userBean.user.friendList}">
        ...
    </p:dialog>
</h:panelGroup>

An alternative is to use PrimeFaces' RequestContext in the bean's action method which allows you to execute JavaScript code programmatically in bean's action method (although this tight-couples the controller a bit too much with the view, IMO).

<p:commandButton value="Delete all friends?" action="#{userBean.deleteAllFriends}" />

with

RequestContext context = RequestContext.getCurrentInstance();

if (!user.getFriendList().isEmpty()) {
    context.execute("deleteFriendsConfirmDialog.show()");
} else {
    context.execute("friendsAlreadyDeletedErrorDialog.show()");
}

---

Unrelated to the concrete problem, your original onclick, while it does not work out in your particular case, shows some poor practices. The javascript: pseudoprotocol is superfluous. It's the default already. Remove it. Also the test against == 'true' is superfluous. Remove it. Just let the EL print true or false directly. The following is the proper syntax (again, this does not solve your problem, just for your information)

<p:commandButton
    onclick="if (#{not empty userBean.user.friendList}) deleteFriendsConfirmDialog.show(); else friendsAlreadyDeletedErrorDialog.show();"
    value="Delete all friends?" />

It would have worked if you were using RichFaces' <a4j:commandButton>.

<a4j:commandButton
    oncomplete="if (#{not empty userBean.user.friendList}) deleteFriendsConfirmDialog.show(); else friendsAlreadyDeletedErrorDialog.show();"
    value="Delete all friends?" />