如果只渲染另一个组件，如何渲染组件？ [英] How to render a component only if another component is not rendered?

问题描述

我有一个页面，用户可以通过Android，iPhone，BlackBerry或未知浏览器访问该页面。我有4个 rich：panel s，每个平台一个，后者是通用的。

I have a page that the user can access via Android, iPhone, BlackBerry or via an unknown browser. I have 4 rich:panels, one for each platform and the latter is a generic one.

代码：

<rich:panel id="dlAndroid" rendered="#{fn:containsIgnoreCase(request.getHeader('User-Agent'), 'Android')}">
    ...
</rich:panel>

<rich:panel id="dlIphone" rendered="#{fn:containsIgnoreCase(request.getHeader('User-Agent'), 'iPhone')}">
    ...
</rich:panel>

<rich:panel id="dlBlackberry" rendered="#{fn:containsIgnoreCase(request.getHeader('User-Agent'), 'BlackBerry')}">
    ...
</rich:panel>

<rich:panel id="dlGeneric" rendered="#{ ---> WHAT TO WRITE HERE? <--- }">

如何渲染最后的 rich：panel 只有在没有其他人被渲染的情况下？

How can I render the last rich:panel only if none of the others has been rendered?

推荐答案

到目前为止，标题中所述的问题具体可以是回答为：

To the point, your question as stated in the title can concretely be answered as:

<rich:panel binding="#{panel1}" ...>
    ...
</rich:panel>
<rich:panel binding="#{panel2}" ...>
    ...
</rich:panel>
<rich:panel binding="#{panel3}" ...>
    ...
</rich:panel>
<rich:panel ... rendered="#{not panel1.rendered and not panel2.rendered and not panel3.rendered}">
    ...
</rich:panel>

然而，在这个特殊情况下，用< c：set> ：

However, in this particular case it's perhaps nicer to alias those long winded expressions with <c:set>:

<c:set var="android" value="#{fn:containsIgnoreCase(header['User-Agent'], 'Android')}" scope="request" />
<c:set var="iPhone" value="#{fn:containsIgnoreCase(header['User-Agent'], 'iPhone')}" scope="request" />
<c:set var="blackBerry" value="#{fn:containsIgnoreCase(header['User-Agent'], 'BlackBerry')}" scope="request" />

<rich:panel ... rendered="#{android}">
    ...
</rich:panel>
<rich:panel ... rendered="#{iPhone}">
    ...
</rich:panel>
<rich:panel ... rendered="#{blackBerry}">
    ...
</rich:panel>
<rich:panel ... rendered="#{not android and not iPhone and not blackBerry}">
    ...
</rich:panel>

请注意，通过隐式获取请求标头的方法较短＃ {header} map。

Note that there's a shorter way to get the request header by the implicit #{header} map.

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