Add a parameter to "external url" menu item

Question

I have a menu in joomla that appears on all pages. Some of the items in the menu should be the same on every page, while others need to be dynamically updated based on the page the user is on. I am trying to create an override for the "external url" menu item type (listed under system links), that would allow me to create a menu item parameter the user could populate. Then, I could use this parameter in the menu template to determine what needs to be added to that particular link.

I have been able to add additional parameters to menu items for custom components by editing their xml files. And I know Joomla allows overrides of these files, but I don't think the "external url" menu item is created from an xml file. How could I add an additional parameter to these menu items? Do I need to create some kind of plugin or am I asking for the impossible?

Answer 1

The External URL menu item also has an XML file (like all backend forms in Joomla). You can find it inside:

administrator/components/com_menus/models/forms/item_url.xml

So inside this file (or the corresponding override for it), you could add something like (within the <fields> </fields>:

<fieldset name="custom" label="custom">
    <field name="menu_custom" type="text"
        label="Custom"
        description="Custom" />
</fieldset>

in order to have your custom tab for your custom fields in the backend.

Update:

To create overrides for model form XML files read here: Overriding Core Components Model Form XML

Answer 2

For anyone else who runs into this problem:

Technically FFrewin's response was what I was looking for, but it was not the solution to the problem. You can't override those xml files like you can for most other components. I ended up using the plugin that was suggested and it works perfectly for me.

http://extensions.joomla.org/extensions/extension/miscellaneous/form-xml-override