Canceling saving of an item via onBeforeSaveField function

Thank you.

I will find the way to do what I want.
A last question :
can I fill fields through another ?

YEs you can try this 2 fields both have different configuration:

RELATED and SCOPE by CATEGORY this will populate the field with thet items of that category

other approuch:

The new SELECT BACK LINKS (something like this) also you can SCOPE by a category.

Let me know if it helped.

I'm sorry, I don't understand.

I explain my wish :
In the frontend, when a user wants to submit a new article (for example) with a link (another field), I would like to be able to retrieve the image (from the link) and store the image's id in another field named image.

I don't know if I'm clear enough.

Merci.

mmm you really need to have an image link?

what about asking user to upload an image to the image field?

I was an example.

Imagine I have a youtube link :

A user just fill in the link, and my script extract the id : lHTAV9H8yK4
the title, and the image (just the link).
I would like to store all these data in different fields (video_id, image, title, link)

its simply create a texte field allow plugin to insert video example jw video
and use {youtube}prefix and {/youtube} suffix
extensions.joomla.org/extensions ... allery/812
regards