Typo3 Fluid, sf_event_mgt extension - how to display only the currently used categories - typo3

Question

By default, the extension shows all in the plugin selected categories even if not used by the event. I would like to display only the currently used categories. Any ideas?
<f:for each="{categories}" as="category">
<f:if condition="{overwriteDemand.category} == {category.item.uid}">
<f:then>
<f:link.action class="button active tiny" action="list" controller="Event" arguments="{overwriteDemand:{category: category}}">{category.title}</f:link.action>
</f:then>
<f:else>
<f:link.action class="button tiny" action="list" controller="Event" arguments="{overwriteDemand:{category: category}}">{category.title}</f:link.action>
</f:else>
</f:if>
</f:for>

Answer 1

first you need a list of categories belonging to the event. this is probably not the Fluid-Variable {categories} (where you hold all your categories as it seems)
probably you need something based on the categoriefield of your event record.
this could be done with a dataProcessor (espec. DatabaseQueryProcessor)

Answer 2

You can just disable the display of inactive categories like in the following code:
<f:for each="{categories}" as="category">
<f:if condition="{overwriteDemand.category} == {category.item.uid}">
<f:then>
<f:link.action class="button active tiny" action="list" controller="Event" arguments="{overwriteDemand:{category: category}}">{category.title}</f:link.action>
</f:then>
<f:comment><![CDATA[
<f:else>
<f:link.action class="button tiny" action="list" controller="Event" arguments="{overwriteDemand:{category: category}}">{category.title}</f:link.action>
</f:else>]]></f:comment>
</f:if>
</f:for>
or remove the codee for the unused categories completely:
<f:for each="{categories}" as="category">
<f:if condition="{overwriteDemand.category} == {category.item.uid}">
<f:link.action class="button active tiny" action="list" controller="Event" arguments="{overwriteDemand:{category: category}}">{category.title}</f:link.action>
</f:if>
</f:for>
The code seems to be from this template: Templates/Event/List.html
IMPORTANT:
Don't alter the original fluid templates but make a copy first into your own sitepackage (or a different extension).
You can adjust the template path for sf_event_mgt then by typoscript to your own templates. At best you do it in the constant editor in the backend.
Like this the changes are kept even if you update the extension, and you always have the original templates available if you need to look at them. It would also be possible to use the original templates on some pages and on other pages your own ones.
The TypoScript template snippet with the constants for the fluid files looks like this, so you know the options you've to search for in the constant editor:
plugin.tx_sfeventmgt {
view {
# cat=plugin.tx_sfeventmgt/file; type=string; label=Path to template root (FE)
templateRootPath = EXT:sf_event_mgt/Resources/Private/Templates/
# cat=plugin.tx_sfeventmgt/file; type=string; label=Path to template partials (FE)
partialRootPath = EXT:sf_event_mgt/Resources/Private/Partials/
# cat=plugin.tx_sfeventmgt/file; type=string; label=Path to template layouts (FE)
layoutRootPath = EXT:sf_event_mgt/Resources/Private/Layouts/
}
...
}

Answer 3

Since version 6.1.0 of the extension, there is the e:category.count() viewHelper available which returns the amount of events assigned to a category. This viewHelper can be used to filter out categories which do not have any events assigned as shown below:
<f:for each="{categories}" as="category">
<f:if condition="{e:category.count(categoryUid: category.uid)} > 0">
<f:if condition="{overwriteDemand.category} == {category.uid}">
<f:then>
<f:link.action action="list" controller="Event" arguments="{overwriteDemand:{category: category}}" class="active button">{category.title}</f:link.action>
</f:then>
<f:else>
<f:link.action action="list" controller="Event" arguments="{overwriteDemand:{category: category}}" class="button button-outline">{category.title}</f:link.action>
</f:else>
</f:if>
</f:if>
</f:for>
Please make sure, that you add the viewHelper namespace xmlns:e="http://typo3.org/ns/DERHANSEN/SfEventMgt/ViewHelpers" to the opening HTML tag of the Fluid template.