Plugin Development using classes – Public & Private Callbacks

WordPress hooks only work with global functions ( or public function inside a class ) – private or protected methods are not available due to their visibility level, so not available to the way WP calls actions or filters.

What you are trying to do is tidy up your code using a class to contain all the functions (
called methods inside a class ), this seems like a good idea, until you review it – and then you notice the bad code smell – you’re writing proxy OOP – not real OOP – and this offers little justifiable benefit.

WordPress is partly responsible, but your plugin design is also responsible – you need to understand the patterns and refactor your plan – OR NOT.. because maybe it works better as procedural code than OOP…