This is just a suggestion.
K2 is way ahead of the content management side of Joomla, and possibly should be entirely a CMS of its own. However one item that's been a bane for me is the inability to assign custom fields (extra fields) to categories rather than just to field groups, similar to how the Joomla custom fields now function.

The issue with only being able to assign field groups to categories, is that one has to create multiple instances of the same field type just to use each in specific category. This creates clutter and confusion.

Consider the scenario:
A category used to display a catalog for books and has field group books with 3 text fields - video, video caption and author name.
Another category is used to display videos and has field group video with 2 text fields - video and video caption.
There has to be dual instances of video and video caption because it's the group that determine the category display instead of the fields.

Hopefully JoomlaWorks will consider:
- Assign extra fields to categories or add single field to multiple groups
- Custom install-able extra fields system
- Option to disable field value auto display in frontend
- Option to disable field label display

Alternatively, JW could consider adjusting K2 to support and output Joomla's custom fields

Hello there,

This extension can assist you, since you can assign multiple groups to a certain category, thus eliminating the need to have the same fields multiple times.

Furthermore you can post this as a feature request in our repo so we can evaluate it. github.com/getk2/k2

Finally, thanks feedback is invaluable to us :)

Krikor thanks for the reply.

You didn't publish a link. However, if you meant the extension called Inceptive Multiple ExtraFields Group at github.com/kmgalanakis/Inceptive-Multiple-Extra-Field-Groups-for-K2, it doesn't seem compatible with 2.8+ because it breaks the K2 tab function and causes the fields of display settings and publishing to all show on one page, and it is chaotic. Such a situation is what makes it quite risky to construct a massive website that is dependent on third party application which may become defunct due to lacking maintenance.

Such a function has to be within the core construct for long term reliability.

Secondly, it still promotes clutter since it creates a tab per group instead of all groups within a single tab and stacked vertically.

I'll certainly follow your advice and submit the suggestion, though the request has been submitted by other users since 2009 (www.joomlaworks.net/forum/k2-en/19900-assign-multiple-extra-field-groups-to-categories).

extensions.joomla.org/extension/multiple-extra-fields-groups-for-k2/

This is the correct link. Mohamed is a great Joomla! dev.
Reach out to him and I am sure he can reassure you about this extension.

What that extension does as far as grouping fields within the extra field tab, I already achieve with an admin override of item view template, using the existing K2 field type header and jQuery wrapAll() to create pseudo groups with accordion tabs, within a single group. However that has long been a bit of a band-aid on non-healing wound for 4 years.

Fields need the ability of assignment to multiple categories. K2 could lose its stronghold without that function since there are other CCKs which support that method.

However, I've begun R&D on a plugin to adapt Joomla's com_field functions into K2. So far the sketching indicate that it should work as expected.

I would really like to see that plugin in action.
Also do open a feature request on the repo.

After digging in, I realized there were too many core K2 classes which had to be overridden by copying the entire class file, and that was not going to jive well with future releases.

Instead of making K2 adapt Joomla's custom field system, I made a plugin and set of library functions to make Joomla Content behave like K2 eg:
-- file download attachment,
-- author details and link to all articles by author,
-- related articles by tags
-- social share buttons
-- poll (not K2 but would be great for K2)
-- video player and playlist
-- audio player and playlist
-- multi-comment applications adaptable using shortcodes [fbcomment] [disqus] [jomcomment] [jcomment]

The plugin also includes methods to make K2 layout very flexible by using shortcodes, which is configured in the category settings via an added text area. The shortcodes also output extra field values by using [field="23"], therefore omitting the need to edit or create additional template overrides to custom arrange extra fields.

One can achieve all sorts of wild displays per category, and even overridable per item. See an example at directory.websitedons.net/k2-item

The attached image shows the item layout setup with shortcodes.

That's very nice Nadal :)
Kudos, the extension seems promising.

Fields have been added to the item tabs to simplify media entry. Is it OK to post a thread about this K2 extension?

Of course it is!!
Feel free to post :)