Show admin page, only if function is being used

Question

I wrote a small function which displays a quote on the page, whenever the function is being called somewhere in a template. Since nobody likes the same quote, I created an admin page for it, where one can change the quote and a few more settings.

Now I want to use this functions.php for several more themes, espescially because it has lots of usefull functions. This quote is not used in every theme. So I want to avoid that people find this quote option in the WP backend, while it is not supported in the templates. So I'm looking for something which does:

if (function "quotes" is used in any template of this theme) {
    Show-admin_page;
}

Of course I could put it in a plugin, but I prefer to keep it in my functions, since I don't want to check everytime whether the plugin is needed or not, and I don't want to write 'plugin depended' templates.

Answer 1

I don't see how that would be possible without parsing every template file. I think a better option would be to either output the quote via a filter on something, like the_content, or via a custom action. The former will let you check if a hook has_filter, the latter will let you check if your custom action has anything hooked to it via has_action.

Answer 2

I would like to suggest that you are doing at least a couple of things wrong.

First, if you want to "share" functions between themes copying functions.php is not a very robust way to do it. You will be copying and re-copying every time you change something.

Second, checking whether a function is used in a theme template is going to be a labor intensive process. You do not want to do that.

There are a couple of things I can think of that are better options.

1. Create a parent theme to house the shared code and child themes to implement it.
2. Use a Must Use Plugin to house the shared code.
3. Though even ordinary plugins make for nicely re-useable code.

Whichever you choose to selectively use the "quotes" code, just provide a helper function to "boot" it. For example:

/* Shared code */
function register_my_custom_menu_page(){
    add_menu_page( 'custom menu title', 'custom menu', 'manage_options', 'custompage', 'my_custom_menu_page', plugins_url( 'myplugin/images/icon.png' ), 6 ); 
}

function my_custom_menu_page(){
    echo "Admin Page Test"; 
}

function init_my_custom_admin_page() {
  add_action( 'admin_menu', 'register_my_custom_menu_page' );
}
/* End Shared code */

/* Boot the shared code in your theme */
init_my_custom_admin_page();

That is pretty rough code. I'd probably use a class to encapsulate everything nicely, for one. It should give you the idea though.