Is it possible to reference a class instead of a function in ‘add_action’? Can’t seem to figure it out. Here is just a basic example of the function in question.
add_action( 'admin_init', 'MyClass' );
class MyClass {
function __construct() {
.. This is where stuff gets done ..
}
}
So yeah, that doesn’t work. I’ve also tried:
$var = new MyClass();
add_action( 'admin_init', array( &$var ) );
And:
$var = new MyClass();
add_action( 'admin_init', array( &$var, '__construct' ) );
And also:
add_action( 'admin_init', 'MyClass::__construct' );
Is there anyway I can do this without having to create a separate function that loads the class? I’d like to be able to just run the classes constructor through the add_action. That’s all that needs to be loaded to get the ball rolling.
No, you cannot ‘initialise’ or instantiate the class through a hook, not directly. Some additional code is always required ( and it is not a desirable thing to be able to do that, as you’re opening a can of worms for yourself.
Here is a better way of doing it:
Of course one could create an interface class to simplify it for the general case even further:
Note that as an interface, you can’t create an object of this type directly, but you could create a sub-class, letting you say:
Which would then automatically add all the hooks, you just need to define what exactly is being done in a subclass and then create it!
On Constructors
I wouldn’t add a constructor as a hook function, it’s bad practice, and can lead ot a lot of unusual events. Also in most languages a constructor returns the object that is being instantiated, so if your hook needs to return something like in a filter, it will not return the filtered variable as you want, but instead it will return the class object.
Directly calling a constructor or a destructor is very, very, very bad programming practice, no matter which language you’re in, and should never be done.
Constructors should also construct objects, to initialise them ready for use, not for actual work. Work to be done by the object should be in a separate function.
Static class methods, and not needing to instantiate/initialise at all
If your class method is a static class method, you can pass the name of the class in quotes rather than
$this
as shown below:Note the use of
__NAMESPACE__
which is required if your class is inside a namespace.Closures
Sadly you cannot avoid the line creating the new class. The only other solution to skipping it would involve boiler plate code that still has that line e.g.:
At which point you may as well skip the class, and just use a function:
But keep in mind you have now introduced the spectre of anonymous functions. There is no way to remove the above action using
remove_action
, and this can and does cause great pain for developers who have to work with other peoples code.On Ampersands
You may see actions used like this:
This is bad.
&
was added back in PHP 4 when objects were passed as values, not as references. PHP 4 is more than a decade old, and hasn’t been supported by WordPress in a very long time.There is no reason to use
&this
when adding hooks and filters, and removing the reference will cause no issues, and may even improve compatibility with future versions of PHPUse this instead:
Example class
Notes:
! class_exists
to avoid calling it twice and place the init caller insideinit
function and the class varstatic
new self
.Here’s an example
Php 5+
Please, leave the
&
out. We’re already beyond php4. 🙂You can trigger events in your class without the need to load it initially. This is handy if you don’t want to load the full class up front, but need to access the WordPress filters and actions.
Here’s a very simple example
This is a very simplified version of Kaiser’s answer but shows in simple terms the behaviour. Might be handy for those looking at this style for the first time.
Other methods can still initiate the object if required. I’m personally using this method to allow optional parts of my plugin to enqueue scripts, but only triggering the object on an AJAX request.
This works for me:
Generally speaking, you wouldn’t add an entire class to a hook. The
add_action()
/add_filter()
hooks expect callback functions, which can be referenced from within a class.Let’s say that you have an
init()
function inside your class, that you want to hook into the WordPressinit
hook.Put your
add_action()
call inside your class, and then identify the callback like so:(Note: I’m assuming your class is properly namespaced; otherwise, be sure to namespace your callback functions.)
You should be able to do it by passing the class name instead of the instantiated object:
(In theory, your other solution should work too
Not sure off the head why it doesn’t. Maybe if you don’t call by reference?)