How to render a JSF component only if at least two children are rendered (title + item)?

Question

I have a:

<h:panelGroup />
  <h:outputText value="title" />
  <h:itemThatSometimesWillShow rendered="sometimes1" />
  <h:itemThatSometimesWillShow rendered="sometimes2" />
  <h:itemThatSometimesWillShow rendered="sometimes3" />
  ...many more

And I would like that, if none of the itemThatSometimesWillShow shows, the whole panel (the title, actually) does not show either.

I did try with composite component's #{cc.childCount} > 1, but I'm not inside a composite implementation, so looks like it will always return 0.

Any idea? (I'm searching for something with js or EL to use in rendered attribute of the parent panelGroup)

BalusC · Answer 1 · 2017-10-13T20:22:36.577

This is achievable with EL 3.0 stream API. My initial attempt was:

<h:panelGroup rendered="#{component.children.stream().filter(c -> c.rendered).count() gt 1}">
    <h:outputText value="title" />
    <h:panelGroup rendered="#{false}">item1</h:panelGroup>
    <h:panelGroup rendered="#{false}">item2</h:panelGroup>
    <h:panelGroup rendered="#{false}">item3</h:panelGroup>
</h:panelGroup>

However, that didn't work quite well. It unexpectedly ran into an infinite loop which ultimately ended with an OutOfMemoryError. It appears that #{component} EL variable still represents the previous component at the moment the rendered attribute is consulted. This is a bit of a chicken-egg issue: the #{component} for current component is only injected if its rendered attribute evaluates true.

Given that, I can see two more options: explicitly find the component by ID as below,

<h:panelGroup id="foo" rendered="#{component.findComponent('foo').children.stream().filter(c -> c.rendered).count() gt 1}">
    <h:outputText value="title" />
    <h:panelGroup rendered="#{false}">item1</h:panelGroup>
    <h:panelGroup rendered="#{false}">item2</h:panelGroup>
    <h:panelGroup rendered="#{false}">item3</h:panelGroup>
</h:panelGroup>

or let it print some CSS class which in turn does a display:none;.

<h:panelGroup styleClass="#{component.children.stream().filter(c -> c.rendered).count() gt 1 ? 'show' : 'hide'}">
    <h:outputText value="title" />
    <h:panelGroup rendered="#{false}">item1</h:panelGroup>
    <h:panelGroup rendered="#{false}">item2</h:panelGroup>
    <h:panelGroup rendered="#{false}">item3</h:panelGroup>
</h:panelGroup>

Great! I'm thinking: isnt't there a method like `component.children.size()`? I'll look for it... — The Student, Oct 20 '17 at 15:09
Yup, exactly that, or `#{component.childCount}` for more effectiveness. It only isn't helpful in solving your specific problem as it doesn't consult the children's `rendered` attribute. — BalusC, Oct 20 '17 at 17:19

score 2 · Accepted Answer · answered Jun 03 '16 at 19:42

2

i would shortly go with this:

<h:panelGroup rendered="{bean.isSometimes()}"/>
  <h:outputText value="title" />
  <h:itemThatSometimesWillShow rended="{bean.isSometimes1()}" />
  <h:itemThatSometimesWillShow rended="{bean.isSometimes2()}" />
  <h:itemThatSometimesWillShow rended="{bean.isSometimes3()}" />

and in the bean:

public boolean isSometimes()
{
    return isSometimes1() || isSometimes2() || isSometimes3();
}

answered Jun 03 '16 at 19:42

tt_emrah

1,043
1
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1

That's what I did for now, thanks! But isn't there a more abstract way? – The Student Oct 20 '17 at 15:06

How to render a JSF component only if at least two children are rendered (title + item)?

2 Answers2