javascript p:commandButton onclick 中的 EL 表达式不会在 ajax 请求上更新/重新呈现？
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EL expression inside p:commandButton onclick does not update/re-render on ajax request?
提问by Murat Derya ?zen
The onclickattribute of my commandButtonhas some EL dependent Javascript inside. To be more specific, here is that piece of code:
onclickmy的属性commandButton里面有一些依赖于 EL 的 Javascript。更具体地说，这是一段代码：
<p:commandButton
onclick="javascript: if('#{userBean.user.friendList.size() gt 0}' == 'true') deleteFriendsConfirmDialog.show(); else friendsAlreadyDeletedErrorDialog.show();"
value="Delete all friends?" />
deleteFriendsConfirmDialogclears the list of friends and updates the @form. The list of friends, commandButton and the dialogs are all in that form.
deleteFriendsConfirmDialog清除好友列表并更新@form. 好友列表、commandButton 和对话框都采用这种形式。
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.
所以我点击按钮，确认对话框出现（因为朋友列表的长度是 gt 0），我确认并清空列表，更新视图。但是，当我Delete all friends?再次单击该按钮时，再次出现确认对话框。由于列表的长度现在为 0，我希望显示错误对话框。
That, I guess, is because the Javascript written inside onclickis not updated (although the button is in the form).
那，我猜，是因为里面写的Javascriptonclick没有更新（虽然按钮在表单中）。
Edit:Changing #{userBean.user.friendList.size() gt 0}to #{not empty userBean.user.friendList}doesn't work neither.
编辑：更改#{userBean.user.friendList.size() gt 0}为#{not empty userBean.user.friendList}也不起作用。
How come? What's wrong here?
怎么来的？这里有什么问题？
Any help appreciated. :)
任何帮助表示赞赏。:)
回答by BalusC
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.
的确。PrimeFaces（和标准 JSF）不会on*在每个请求的基础上重新评估属性中的 EL 。它只发生在每个视图的基础上。然而，RichFaces 在<a4j:xxx>组件中做到了这一点。
You need to solve the problem differently. I suggest to use the visibleattribute of the <p:dialog>instead.
您需要以不同的方式解决问题。我建议改用 the 的visible属性<p:dialog>。
<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' RequestContextin 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).
另一种方法是RequestContext在 bean 的 action 方法中使用 PrimeFaces' ，它允许您在 bean 的 action 方法中以编程方式执行 JavaScript 代码（尽管这将控制器与视图紧密耦合，IMO）。
<p:commandButton value="Delete all friends?" action="#{userBean.deleteAllFriends}" />
with
和
RequestContext context = RequestContext.getCurrentInstance();
if (!user.getFriendList().isEmpty()) {
context.execute("deleteFriendsConfirmDialog.show()");
} else {
context.execute("friendsAlreadyDeletedErrorDialog.show()");
}
Unrelatedto 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 trueor falsedirectly. The following is the proper syntax (again, this does not solve your problem, just for your information)
与具体问题无关，您的原始onclick，虽然它在您的特定情况下不起作用，但显示了一些不良做法。该javascript:pseudoprotocol是多余的。已经是默认了。去掉它。此外，针对的测试== 'true'也是多余的。去掉它。只是让EL打印true或false直接。以下是正确的语法（同样，这不能解决您的问题，仅供参考）
<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>.
如果您使用 RichFaces' ，它会起作用<a4j:commandButton>。
<a4j:commandButton
oncomplete="if (#{not empty userBean.user.friendList}) deleteFriendsConfirmDialog.show(); else friendsAlreadyDeletedErrorDialog.show();"
value="Delete all friends?" />
