c:for ui:repeat中的每个素面(例如p:panelgrid) [英] c:forEach inside primefaces(e.g. p:panelgrid) inside ui:repeat

问题描述

我必须动态地产生一个表列表.每一个都有可变数量的列(具有固定的行).

要执行此操作，我首先将<p:panelGrid>放在<ui:repeat>内:这样我就正确地生成了一个表列表.

然后，为了动态生成列，我尝试将<ui:repeat>或<c:forEach>都放在<p:panelGrid>内.结果我没有得到任何行.

我在这里写了一个最小的例子.在bean testBackingBean中，我定义(并初始化了)变量ArrayList<ArrayList<String>> tables.这是无法产生预期结果的xhtml:

<ui:repeat var="table" value="#{testBackingBean.tables}">
    <p:panelGrid>
        <f:facet name="header">
            <p:row>
                <p:column >header of #{table}</p:column>
            </p:row>
        </f:facet>
        <p:row>
            <c:forEach var="row" items="${table}">
                <p:column>#{row}</p:column>
            </c:forEach>
        </p:row>
    </p:panelGrid>
</ui:repeat>

值得注意的是，标题行正确地将#{table}转换为字符串.问题是我看不到任何数据行.

此外，如果我使用<table>而不是<p:panelGrid>，一切都会按预期进行.

此外，我尝试了<c:forEach>和<ui:repeat>的不同排列，但没有成功.

那么，我该如何动态地生成更多的表(使用素面)并设置出数量惊人的列呢?

谢谢！

我想使用两个<c:forEach>，但是即使只有一个<c:forEach>，我也会得到一个空结果.实际上，如果我尝试以下xhtml:

<c:forEach  items="${testBackingBean.tables}" var="tabella">
    current element: #{tabella}
</c:forEach>

然后我得到一个空结果. (我知道，这是一个不同的问题)

解决方案

从XHTML源代码到生成的HTML输出的过渡是一个两步过程.

1. 首先，在视图构建期间，将解析XHTML源代码并将其转换成Java实例树，该树代表JSF UI组件树，由FacesContext#getViewRoot()提供.

2. 然后，在视图渲染期间，JSF UI组件树会生成HTML输出，并从UIViewRoot#encodeAll()方法开始将其写入HTTP重新操作.

Taghandlers 像所有JSTL <c:xxx>标记，几个JSF <f:xxx>标记和仅几个Facelets <ui:xxx>标记在视图构建期间运行. UI组件像所有JSF <h:xxx>标签，多个Facelets <ui:xxx>标签和仅几个JSF <f:xxx>标签在视图渲染期间运行.

仅在视图渲染期间可用，而在视图构建期间不可用. <c:forEach>基本上是在视图构建期间将要运行的#{null}作为值检索的.

您可以通过将外部<ui:repeat>替换为<c:forEach>来解决此问题.尽管我不知道您是否能更好地使用<ui:repeat><p:dataTable><p:columns>来代替.

另请参见:

• JSF2 Facelets中的JSTL ...有意义吗?

I have to dinamically produce a list of tables. Each of these have a variable number of columns (with fixed rows).

To perform this I first put a <p:panelGrid> inside an <ui:repeat>: so I correctly produced a list of tables.

Then, to dinamically produce the columns, I tried put both an <ui:repeat> or a <c:forEach> inside the <p:panelGrid>. In the result I obtain no rows.

I written a minimal example here. In the bean testBackingBean, I have defined (and initialized) the variable ArrayList<ArrayList<String>> tables. This is the xhtml that does not produce the expected results:

<ui:repeat var="table" value="#{testBackingBean.tables}">
    <p:panelGrid>
        <f:facet name="header">
            <p:row>
                <p:column >header of #{table}</p:column>
            </p:row>
        </f:facet>
        <p:row>
            <c:forEach var="row" items="${table}">
                <p:column>#{row}</p:column>
            </c:forEach>
        </p:row>
    </p:panelGrid>
</ui:repeat>

Noteworthy the header-row correctly converts #{table} into string. The problem is that I see no rows of data.

Also, if I use the <table> instead of the <p:panelGrid> everything work as excpected.

Also, I tried different permutations of <c:forEach> and <ui:repeat> with no succes.

So, how can I dinamically produce more tables (using prime-faces) and set a dinamical number of columns?

Thanks!

EDIT: I would like to use two <c:forEach>, but even with one only <c:forEach> I get an empty result. In fact if I try the following xhtml:

<c:forEach  items="${testBackingBean.tables}" var="tabella">
    current element: #{tabella}
</c:forEach>

then I get an empty result. (I know,this is a different question)

解决方案

The transition from the XHTML source code to the generated HTML output is a two-step process.

1. First, during view build time, the XHTML source code is parsed and turned in a tree of Java UIComponent instances representing the JSF UI component tree, as available by FacesContext#getViewRoot().

2. Then, during view render time, the JSF UI component tree produces HTML output and writes it to the HTTP resopnse, starting with UIViewRoot#encodeAll() method.

Taghandlers like all JSTL <c:xxx> tags, several JSF <f:xxx> tags and only a few Facelets <ui:xxx> tags run during view build time. UI components like all JSF <h:xxx> tags, several Facelets <ui:xxx> tags and only a few JSF <f:xxx> tags run during view render time.

The <c:forEach> is a taghandler and the <ui:repeat> is an UI component.

In other words, the UI components which are declared inside <c:forEach> are recreated multiple times in the JSF component tree based on <c:forEach items> during view build time which in turn individually produce each their own HTML output during view render time. The UI components which are declared inside <ui:repeat> are created only once in the JSF component tree during view build time which in turn are reused multiple times based on <ui:repeat value> to produce HTML output during view render time.

Your concrete problem is caused by the fact that <ui:repeat var="table"> is only available during view render time, not during view build time. The <c:forEach> is basically retrieving a #{null} as value when it's about to run during view build time.

You can solve this by replacing the outer <ui:repeat> by <c:forEach>. Although I wonder if you couldn't better use <ui:repeat><p:dataTable><p:columns> instead.

See also:

• JSTL in JSF2 Facelets... makes sense?

这篇关于c:for ui:repeat中的每个素面(例如p:panelgrid)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！