(Reading time: 7 – 11 minutes)
Wait! Stop!
There’s much more here than source code. You can skip right over the register_activation_hook example code. Unless you’re desperately seeking solutions, then you want to read every word.
Still with me? Cool. Let’s get started.
Technical documentation is hard to read and harder to write. As a programmer, you aren’t rewarded for writing documentation, no matter what management says, so documentation tends to be lean, spare.
As a reader, you know you’re putting on the turswiry hat before you even crack open the manual.
When you finally break out the manual, you’re invariably faced with learning about how complicated it all is. Then,
Once you figure it out on your own, you can’t say the man pages don’t say that. – Jason Cox.
Wisdom from East Tennessee indeed.
It’s that “figure it out on your own” part that’s so hard. It takes a lot of practice, both to do the figuring, and knowing when you need to take the time to do the figuring.
Because it is time consuming.
Here’s my practice “figuring it out” for today.
(Non-programmers, skip past the code).
Example code from WordPress.org forum
WordPress is a large and rich application. It’s fairly well written; I’ve seen far worse code. And it’s fairly well-documented.
But there are still a lot of dusty corners. One of these is the register_activation_hook function. Most plugins need to use, but there’s not a lot of accurate discussion about exactly how to use it.
I was poking around for some example code, and ran across this snippet posted by Gleb Esman. Gleb seems pretty cool, he’s the author of the MemberWing plugin and service. But he didn’t get this one right, and I’m going to show you why. Let’s take a look:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 | <?php /* Plugin Name: A Test Description: A Test */ require_once (dirname(__FILE__) . '/my_other_file.php'); // This code *will not* work. Activation hook function must be defined in the main plugin file. //register_activation_hook (dirname(__FILE__) . '/my_other_file.php', 'my_other_function'); //(Dave) But this code works just fine! register_activation_hook (dirname(__FILE__) . '/activation1.php', 'my_other_function'); register_deactivation_hook (dirname(__FILE__) . '/activation1.php', 'clean_em_up'); // This code will work. //register_activation_hook (__FILE__, 'test_activated'); // This is correct way to declare/access globals. global $some_var; // globals must be declared explicitly. Without this you will not be able to access '$some_var' from within 'test_activated()' function. $some_var = 'hey'; //=========================================================================== function test_activated () { global $some_var; // Now it will be 'hey'. // This function is defined in 'my_other_file.php' my_other_function (); // This will not work, so don't try. If you need logging write something in temporary log file in here via fopen/fwrite. // If you want to quickly test if your activation hook works - put exit() into it. At least you'll see error during activation. echo 'test_activated called!'; } //=========================================================================== ?> |
First, please accept my apologies for the misaligned line numbers. This is a Thesis CSS issue, the table layout design between Thesis and the plugin doesn’t work very well. But it’s still workable. Let’s walk through it line-by-line:
- Line 3: the plugin name. Critical. We’ll return to this later.
- Line 7: I’ve listed this file below as well, we’ll look at it line by line next.
- Line 10: Doesn’t work, true, but the explanation is wrong.
Fact: WordPress will register any callback in scope.
The problem here is that activation hook operates on the plugin name. The name of the file (line 10) containing the callback is irrelevant.
- Line 13: Registering the callback with the correct filename works.
- Line 13: (Bonus) register_deactivation_hook works too.
I’ve left the rest of the code in place so that you can compare my additions linewise with the original register_activation_hook example.
Callbacks in different file
Now we need to take a look at the code in my_other_file.php. Having these functions in a different file is irrelevant for a plugin this small, but it does serve a useful purpose for testing. For larger applications, separating important parts of the code is an important principle of software design.
1 2 3 4 5 6 7 8 9 10 11 | <?php /* Callback for activation hook */ function my_other_function() { add_option('activation1','Activated'); } /* Callback for deactivation hook */ function clean_em_up() { delete_option('activation1'); } ?> |
This is easy stuff, the callbacks just add or remove an option in the WordPress options table.
When you run the code presented in these two listings, take a look at your options database, as shown in this screenshot:
register_activation_hook test using options database
There’s other ways to check, but this is pretty fast, and if you aren’t familiar with the options table you need to be.
Why is register_activation_hook so hard?
I can’t speak for everyone, but here’s what I think:
- PHP variable scoping rules feel kooky coming from a C/C++/Java background. PHP looks like C, smells like C, but doesn’t really walk like C. Trouble comes when programmers absent-mindedly crank out PHP code, unaware of the differences in scoping rules.
- Callbacks give people trouble, even these activation/deactivation functions which are so simple they don’t even take arguments.
- Man pages are inaccessibly written, and often out of date. But manual should be the first place to start. If the manual has test code, run it to check it’s accuracy.
- Even fewer people read the code. The comments for register_activation_hook are crystal clear about what’s expected. If only people would read the source!
You should probably jump over to Reverse Engineering Activation Hook In WordPress Plugin API for more information. This is not really a series of articles… yet. Although I do have at least a couple more articles to write on register_activation_hook. Maybe three or four more. At the end of the last article (that is, when I get tired of writing them), I’ll give you a two-step procedure ensuring you will never, ever have trouble with this function again.
Ok, enough preaching… here’s something for you scanners…
What’s in it for me?
More work, if you’re so inclined. But this is good work. Your work.
Here’s the deal. My friend Deacon and I have a long running discussion on deliberate practice. We both crave personal and professional excellence, and we believe that the path to mastery is in the practice of mastery. Deacon cuts wood blocks. I cut code.
Part of our inspiration comes from this little book, George Leonard’s Mastery. In about 100 small pages, Leonard lays out how mastery is achieved through practice. Practice in the sense of “doing what you do” on a regular basis, with deep concentration.
Practice puts the journey first.
The means become the ends.
Here, taking on some silly misconceptions about some random WordPress function is not what’s important.
Instead, the process of examining the problem, understanding why the problem exists, and constructing an elegant solution is my path to mastery.
I don’t care about register_activation_hook. I care about:
- Understanding WordPress coding conventions. Understanding this code helps me “get inside the developer’s heads.” I want to think how they think. That’s when the “programming” ends… and the creativity begins.
- Learning PHP behavior, specifically, variable scoping rules. Same as above: practice the programming so I don’t have to think about it.
- Ensuring my plugins work correctly when I need to invoke the activation hook. I have a legitimate need to understand how this function works.
- And… (long time readers know what’s coming) smacking down an under-served keyword. Actually, two. An hour of free blog post engineering to the first person who guesses my second keyword.
Learning the intricacies of register_activation_hook is just the convenient vehicle carrying me further along my path.
What’s your path to mastery?
Do you have a regular practice? If so, tell us about it!
