JSF中的条件变量定义 [英] Conditional variable definition in JSF

问题描述

我想根据条件更改变量值 所以我尝试了以下方法:

i want to change the variable value based on a condition so i tried the following:

<h:head>

    <ui:param name="userCase" value="Insert" />

    <ui:fragment rendered="#{employee.employeesBulkInsert==false}">
       <ui:param name="userCase" value="Update" />
    </ui:fragment>

       <title>#{userCase} Employee </title>

</h:head>

但是在更新情况下它不起作用，它显示一个空字符串，为什么有什么主意?

but it doesn't work in the update case, it shows an empty string, any ideas why ?

我知道还有其他解决方案，例如在backing bean中定义变量，或者直接在title标签上创建条件ui片段，但是我想知道为什么上面的方法不起作用，请告知，谢谢.

i know that there are other solutions like defining the variable in the backing bean, or make the conditional ui fragment on the title tag directly, but i want to know why the above is not working, please advise, thanks.

推荐答案

<ui:fragment>是渲染时标记，而<ui:param>是标记处理程序(通过缺少rendered可以轻松识别标记处理程序属性).因此，在构建视图时，无论<ui:fragment>的结果如何，都将设置<ui:param>. <ui:fragment>的rendered属性仅在将呈现已构建的视图时评估.

The <ui:fragment> is a render-time tag while the <ui:param> is a tag handler (tag handlers are easily recognizeable by the absence of the rendered attribute). So when the view get built, the <ui:param> is set, regardless of the outcome of <ui:fragment>. The rendered attribute of <ui:fragment> is only evaluated when the already-built view is to be rendered.

您想改为使用标记处理程序来创建条件，例如JSTL <c:if>.

You want to make the condition using a tag handler instead, such as JSTL <c:if>.

<ui:param name="userCase" value="Insert" />

<c:if test="#{not employee.employeesBulkInsert}">
    <ui:param name="userCase" value="Update" />
</c:if>

(请注意，我删除了不必要的布尔==false比较)

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