As you use object-oriented programming with WordPress more and more, you’re going to encounter new sets of problems. These problems aren’t as simple as the ones that you encountered when you started. But that’s also good news. It also means that you’re making progress.
One set of problems that you start to encounter as you advance in your use of object-oriented programming deal with scaling. As your code has more and more classes, it becomes a challenge to assemble these classes together. That’s why in the past we looked at how to design a class whose job was to do that.
But there are other problems that come with having a lot of classes in your code. It’s how much your classes depend on other classes. This is what we call coupling in programming. (Not just object-oriented programming.)
To help with coupling, a famous software engineer (Robert C. Martin who’s also known as Uncle Bob) created the dependency inversion principle. It helps you decouple your classes by making dependencies external to them. (There’s more to it than that. But this is one of the core elements of the dependency inversion principle.)
This reduces coupling but creates a new problem as well. That problem is that you can’t initialize objects inside your class anymore. You have to pass them to your own object through its constructor or some other method like a setter method.
This makes it even harder to assemble your classes together. This is why software engineers created dependency injection. It’s a programming technique that helps solve this problem.
Most web application frameworks use it in some form or another. But that’s not the case with WordPress since a lot of its code isn’t object-oriented. That said, if you want to build an object-oriented plugin for WordPress, it’s pretty much mandatory. Lucky for us, it’s not that hard to use dependency injection in your own code!
Continue reading Using dependency injection with WordPress
A WordPress plugin can have a lot of different components. For example, some might need to use shortcodes to achieve their purpose. While others might need to create custom post types.
But one component that almost every plugin needs is an admin page. (Or they might even need more than one!) That said, designing an admin page using object-oriented programming isn’t that straightforward. There are a lot of different moving pieces that you have to take in consideration in your design.
A well-designed admin page class will combine these different moving pieces into a cohesive class. The key to achieving this is to understand the role of these different moving pieces in the larger picture of an admin page. We’ll do that by analyzing what makes up an admin page in the first place.
Continue reading Designing a class representing a WordPress admin page
Have you ever worked on localization with other web frameworks? If so, you might be familiar with the idea of using keys to identify translation strings. These keys are how your translation system finds the localized text to use inside your application.
If you’ve been doing localization with WordPress, you know that it doesn’t work that way. With WordPress, you use the original (usually English) content string as your translation key. This can be convenient because you always know what the original string was.
That said, it’s still possible to do WordPress localization using keys instead content strings. This can be useful if you come from these different programming backgrounds. You might like to keep working the way you’re used to. Let’s look at how you can do that!
Continue reading How to use placeholders for WordPress translations
No programming concept frightens programmers more than regular expressions. For a lot of us, seeing code with regular expressions in it can bring a sense of dread and anxiety. We often have no idea what’s going on or how a regular expression does what it does.
That said, regular expressions are a really powerful tool. (That’s why they’re used so much.) There’s always a problem that you can solve with a regular expression around the corner. (Or you can always imagine one!) On top of that, you can use them almost anywhere.
The good news is that you can get over that fear of regular expressions! Learning the basics is often enough to solve a wide range of problems. So let’s go over them together!
Continue reading Beginner’s guide to regular expressions
Much like the plugin API, it’s almost impossible to build a plugin without using the options API. This can be a problem if you’re trying to learn object-oriented programming with WordPress. You need a way to build a class around it.
Lucky for us, this is a lot less complicated to do than with the plugin API. The options API is really nothing more than an API around a data store. Our job as designers is simple. We need to design a class that mirrors this API.
That said, we don’t have to limit ourselves to just copying the options API as is. We can also push things further by adding some extra functionality around it. This is what makes designing a class around the options API so interesting.
Continue reading Designing classes for the WordPress options API
If you use object-oriented programming, there’s a good chance that you’re familiar with the constructor. It’s this special method that an object-oriented programming language uses to initialize a new object. In PHP (and a lot of other object-oriented programming languages), the
__construct method is a special method reserved for the role of constructor.
The role of the constructor isn’t always well understood. This is especially true when you’re new to object-oriented programming. You know the method exists, but you’re not too sure how to use it.
This can lead to some less than ideal practices around constructors. This is especially true in the WordPress world where two such practices are popular. First, there’s the habit of putting hooks in the constructor. And, because of that habit, WordPress developers tend to overuse the singleton pattern.
These two practices show a misunderstanding of the role that a constructor plays inside a class. This isn’t how object-oriented programming wants you to use constructors. There are other ways to solve those problems without sacrificing the role of a constructor.
Now, this isn’t to say that constructors don’t have any problems either. They do! In fact, that’s why we’re looking at the static factory method pattern. It solves one common problem that constructors have in PHP.
Continue reading Using the static factory method pattern with WordPress
Most of us are familiar with how a web application works. We know that when we enter an URL in our browser, it’ll contact a web server who’ll return some HTML. The browser will then make follow-up requests and then render the web page. (This is a simplification! But that’s the main idea.)
But what’s happening on the web server returning HTML? How is the web server getting the HTML that it returns to our browser? And, to be even more specific, how does this happen in PHP?
This isn’t something that most of us know how to answer. We know (or at least should know!) how to build a PHP website. But what happens between our PHP code and the browser is a bit of a mystery.
There’s a good chance that you’re thinking, “Well, my site loads. Why should I think twice about this?” And that’s true! But the truth is that knowing how a PHP application works can be useful.
It can affect how you design your PHP application. But it’s also important if you’re looking to improve its performance. For example, it’s hard to understand PHP application caching if you don’t understand how a PHP application works.
Continue reading How does a PHP application work?
As WordPress developers, we often have to generate HTML content for our plugins. (And, if you’re building a theme, that’s pretty much mandatory!) But generating HTML inside a function or method is messy. You have to close your PHP tag, write your HTML, reopen your PHP tag and so on.
This combination of HTML and code isn’t ideal. You’ve coupled your templating to your code in a way that often doesn’t scale well. That’s why it’s common to see such functions or methods grow out of proportion.
The common cause of that is adding conditional logic into the HTML code. This increases the complexity of the code and reduces its readability. So we’d like to avoid that if possible.
It’s worth pointing out that mixing HTML and PHP isn’t bad per se. After all, PHP is also a templating language. We just want to create a proper delimitation between what is regular PHP code and what is PHP template code.
So let’s find a solution to this problem! The twist (well it’s not really a twist for this site…) is that we’re going to use object-oriented programming to do it. We’ll design a class that generates HTML using PHP template.
Continue reading Designing a class to generate HTML content in WordPress
As WordPress developers, we often need a way to store and retrieve data. The most common reason for that is that we need to store and retrieve settings for our plugin or theme. But the reality is that there are countless of other reasons why you’d need to store and retrieve data.
So how do we do it? Well, the primary tool that we have at our disposal to do this is the options API. It’s an API that offers a way for us to store and retrieve data from the WordPress database.
It’s pretty much as indispensable as the plugin API. We often can’t build anything in WordPress without it. That’s why it’s worth looking a bit deeper at how it works.
Continue reading WordPress for the adventurous: Options API
So let’s talk about coupling! Coupling is a complicated problem because you can never get rid of it completely. All that you can do is control how much it spreads. And there’s more than one way to do that.
One of these ways is the dependency inversion principle. It’s one of the most important principles in object-oriented design. And it’s why it’s part of the famous SOLID design principles. (It’s the “D” in SOLID.)
The dependency inversion principle isn’t something that you see with WordPress. That’s because most WordPress developers don’t use object-oriented programming. (But it’s always a good time to start if you’re not using it!) And the dependency inversion principle only helps when you’ve been using it for a while.
But what makes the dependency inversion principle special? Why is it such almost a mandatory aspect of object-oriented design? These are good questions that you deserve an answer to.
Continue reading Dependency inversion principle and WordPress