How to add an error message when returning false in the onContentBeforeSave event?

Question

I work in a functionality in which I must validate some fields before saving, if a condition is not met I must indicate abort the save process, according to the documentation of the onContentBeforeSave event I do this by returning false, this works fine, but I would like to add a personalized message. Right now when return false, the following message is displayed in the view

I understand after the colon a personalized message is expected. How I do this?

This is the plugin code I am trying

<?php

defined( '_JEXEC' ) or die( 'Restricted access' );

class plgContentMyPlugin extends JPlugin
{
    public function onContentBeforeSave($context, &$article, $isNew, $data)
    {
        if ($context === 'com_content.article') {
            $field1 = $data['com_fields']['field1'];
            $field2 = $data['com_fields']['field2'];

            if (!empty($field1) && empty($field2)) {
                return false; // here, how can I attach a message?
            }

            $date = strtotime($field1);
            $now = time();

            if ($date > $now) {
                return false; // here, how can I attach a message?
            }
        }

        return true;
    }
}

Thanks in advance

Answer 1

You can throw an Exception:

if ($date > $now)
{
    throw new RuntimeException(JText::_('PLG_CONTENT_MYPLUGIN_SOME_ERROR'));
}

Or use setError() on the table object:

if ($date > $now)
{
    $article->setError(JText::_('PLG_CONTENT_MYPLUGIN_SOME_ERROR'));

    return false;
}