[wp-trac] [WordPress Trac] #32708: Customizer Menus: add hooks to the WP_Customize_Nav_Menus class so it can be extended

[WordPress Trac]

#32708: Customizer Menus: add hooks to the WP_Customize_Nav_Menus class so it can
be extended
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 Reporter:  imath                    |       Owner:  valendesigns
     Type:  defect (bug)             |      Status:  closed
 Priority:  normal                   |   Milestone:  4.3
Component:  Customize                |     Version:  trunk
 Severity:  normal                   |  Resolution:  fixed
 Keywords:  has-patch needs-testing  |     Focuses:
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Comment (by Chouby):

 Hi!

 Thank you for fixing this ticket. It should help plugins adding custom
 menu items. However by default we get a standard form, and I don't see how
 to customize it.

 Currently, in Polylang, I have a custom menu item with a custom form.
 Rendering the form can be achieved either by using the
 'wp_edit_nav_menu_walker filter' or JS. I use the second as the first is
 subject to conflicts with other plugins. Saving the user input is
 obviously done in a function hooked to the action
 'wp_update_nav_menu_item'.

 Now I am trying to include this custom menu item in the customizer menus
 and hopefully to be ready for the final release of WP 4.3, but I am
 lacking basic comprehension of the internals of the customizer menus.

 Adding the menu item using the filters provided by this ticket was
 straightforward. I have two issues:
 1. Rendering the form is not as obvious for me. In Appearance->menus, I do
 it binding a function to the click events on the form 'update-nav-menu'.
 Here I tried the same approach using the form 'customize-controls' but for
 some reason, this does not react on clicks when we are adding a menu item
 (thus this works for pre-existing items, not the newly added ones).
 2. Of course, changes to the form are not propagated to the preview and
 worse, the 'wp_update_nav_menu_item' is not fired when I click on save and
 publish (for what I understood, the action is fired only for modified
 items, but currently my custom form does not inform the customizer of its
 changes).

 Is there a documentation somewhere which explains the internals of the
 customizer menus?
 How the form is created when adding a new item? Do we need a new filter to
 customize the form?
 How to propagate changes to the preview and save them to the DB?

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Ticket URL: <https://core.trac.wordpress.org/ticket/32708#comment:30>
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