Pull Request for Issue # .

Summary of Changes

This patch use namespaces to load Joomla! libraries and accept multiple values as array for filtering.

Also add the option to set context value in the xml fields. For example:

        <field
                name="article"
                type="sql"
                label="COM_EXAMPLE_FORM_ARTICLE"
                sql_select="c.id, c.title"
                sql_from="#__content AS c"
                sql_order="c.id ASC"
                sql_filter="catid"
                key_field="id"
                value_field="title"
                context="com_example.list_view_example"
        />

Into the documentation for custom fields is well explained how to use default filters setting sql_default_{field} and a static value but is not explained how to set dynamic variables using user states for filtering. (see testing)

Testing Instructions

Using the last field example, we can see that we set sql_filter as catid . For filtering we must to set into our view.html.php file, using the setUserState method a value or an array for multiple values. For example:

$multiple_values = array(3, 5, 7); 
Factory::getApplication()->setUserState("com_example.list_view_example.filter.catid",  $multiple_values);

This is going to filter into the catid field using the values declared in the variable $multiple_values

Expected result

We should get the list filtered correctly using the static or dynamic values.

Documentation Changes Required

Dynamic filtering must to be added to:

https://docs.joomla.org/Special:MyLanguage/SQL_form_field_type