Before you can create a path or link to another page on your site, you'll need to know the route (unless there is already a variable available for the URL you need). Finding a route can be a tricky task unless you have the right tools. In this tutorial, we'll show how tools like Webprofiler, Drush, and Grep can be used to get route information for a page, so that you can use functions that need a route as a function parameter.

In this tutorial we'll:

Hooks allow modules to alter and extend the behavior of Drupal core, or another module. They are one of the various ways that code components in Drupal can communicate with one another. Using hooks a module developer can change how core or another module works -- without changing the existing code. As a Drupal developer, understanding how to implement and invoke hooks is essential.

In this tutorial we'll:

How do you figure out what hooks are available to implement? How do you know which hook to implement to accomplish a task?

The list of hooks that are available to implement in your custom Drupal module varies depending on the modules enabled for a site. Each module can optionally invoke new hooks. There are also some hooks invoked by Drupal core subsystems like Form API that are always present. This can make it a little bit tricky sometimes to figure out what hooks are available, and which one to implement.

In this tutorial we'll look at:

The Drupal plugin system allows a particular module or subsystem to provide functionality in an extensible, object-oriented way. The controlling module defines the basic framework (interface) for the functionality, and other modules can create plugins (implementing the interface) with particular behaviors. Plugins are grouped into plugin types. Each plugin type is managed by a plugin manager service, which uses a plugin discovery method to discover provided plugins of that type and instantiate them using a plugin factory.

Knowing how to define a new plugin type will allow you to write modules that are more extensible, and more configurable. In doing so you'll learn more about best practices in decoupling code within your module, and get an in-depth look at how the plugin system works. Even if you're not defining a new plugin type in your own module, understanding how the system works will give you more insight into how many parts of Drupal work. This is essential knowledge for anyone developing modules for Drupal.

Before you can create a new plugin of any type you'll need to figure out where the plugin implementation and its metadata should live in the code base so that the plugin manager can find plugins and examine what functionality instances of the plugin type are expected to provide.

In this tutorial we'll:

In order for a plugin manager to locate instances of individual plugins within the Drupal code base it needs to know where to look, and how to interpret the data that it finds. This process is called plugin discovery and can be accomplished in a few different ways.

In this tutorial we'll look at what plugin discovery is doing at a high level, and then talk about the various plugin discovery methods you can choose from when defining a new plugin type.

Goal

Understand the use case for each of the plugin discovery methods provided by Drupal core.

Plugin derivatives allow a single plugin to act in place of many. This is useful for situations where user-entered data, or other dynamic configuration, might have an impact on available plugins. Or, put another way, any time you need to be able to dynamically generate plugin definitions.

In this tutorial we'll:

Some events are dispatched by Drupal core, some by underlying Symfony components, and some by contributed modules. The list of events that you can subscribe to in order to tie into Drupal varies depending on the modules you've got installed. This can make it tricky to get a complete list.

In this tutorial, we'll look at a few different ways you can get a complete list of the available events for your Drupal application, as well as where to find documentation for those events.

Modules or subsystems can dispatch events in order to allow another developer to subscribe to those events and react to what's happening within the application. As a module developer you'll learn how to:

• Define, and document, new events
• Define new event objects
• Use the event dispatcher service to alert event subscribers when specific conditions are met in your own code.

By the end of this tutorial you should be able to explain the use case for dispatching events, and be able to trigger one more events from within your own code.

Annotations are specially-formatted PHP docblock comments that are used for class discovery and metadata description. While it is technically possible to use annotations for other purposes, at the moment Drupal only uses them for the plugin system.

In this tutorial we'll look at:

Themes and modules can alter the list of theme hook suggestions in order to add new ones, remove existing ones, or reorder the list. This powerful feature allows for the definition of custom logic in your application that can tell Drupal to use different templates based on your own unique needs. You might for example; use a different page template for authenticated users, or a custom block template for someone's birthday.

In this tutorial we'll cover:

Drupal provides module developers several different methods for creating the different types of links we see on a typical page. In this tutorial we'll see how these different types of links relate to each other, and when you might want to make use of them.

In this tutorial we'll provide an overview of the following concepts:

Modules can provide action links to make common operations more readily available within a particular context. For example, a site administrator visiting the content management page may be interested in adding content. If you've ever noticed the Add content button on this page, that's an example of an action link. In this tutorial we'll take a look at how custom modules can provide these action links to make it easier for users to interact with our site.

Goal

Learn what action links and local actions are and how they are added to custom modules.

Local task links are the tabs you see when logged in as an administrator viewing a node on a Drupal site. In this tutorial we'll take a look at how local tasks are added within a custom module. We'll also see how to alter local tasks provided by other modules via hook_menu_local_tasks_alter().

Goal

Understand what local tasks are and how to implement or alter them within a custom Drupal module.

The core structure of Drupal's Render API is the render array, which is a hierarchical associative array containing data to be rendered and properties describing how the data should be rendered. As a module developer you'll use render arrays to describe the content your module controls in order to output it on a page as HTML, or as part of a response in another format like JSON. As a theme developer, you'll manipulate render arrays in order to affect the way content is output on the page.

In this tutorial we'll learn:

Strings of simple HTML and plain text can be defined in a render array using the #markup and #plain_text element types. In this tutorial we'll look at:

• Adding simple strings to a render array so they appear as HTML on the page
• When to use #markup and #plain_text in your code

By the end of this tutorial, you should be able to add simple strings of HTML and plain text to a render array.

Drupal makes it easy to convert an array of strings to an ordered or unordered HTML list using '#theme' => 'item_list' elements in a render array. This is commonly done by module developers to display a list such as links to content, the values of settings in a module, or the names of everyone who has viewed a page. Displaying lists is a super common task for a content management system.

In this tutorial we'll look at:

#prefix and #suffix are two commonly used examples of standard properties. That is, they are available for use on any element in a render array regardless of the element #type or #theme property's value. They are a great way to add additional layout markup to an element in a theme-agnostic way.

In this tutorial we'll:

There are a bunch of existing render elements, most commonly Form API elements. You need to know how to discover and make use of existing elements. In this tutorial, we'll learn how to:

• Locate a list of elements provided by Drupal core
• Figure out what properties apply to each element

• Use any render element type when defining content or forms in our code

Some Render API properties, like #pre_render, #element_validate, and #lazy_builder are considered callable. Rather than receiving a static value, they contain a pointer to code that should be called at a specific time during the process of rendering a render element. Callbacks are used in some cases to return a value that can be substituted into the render array, and in other cases given the opportunity to manipulate the current element in the array directly.

In this tutorial, we'll:

This tutorial looks at the steps that Drupal goes through to obtain a render array for an incoming HTTP request, transform the render array into HTML, and then return it to your browser. We provide an outline of the process and links to resources for more in-depth information. We also take a more thorough look at the HtmlRenderer which converts a render array into HTML. Knowing how the render arrays you write in your code are ultimately used can help you optimize Drupal's Render API to describe your module's content.

Linking to things is probably one of the first things you learned how to do as a web developer. Anchor tags are the framework of how the world wide web works. So it's important to know how to create them in Drupal. Chances are you'll be doing a lot of it.

Creating links to things in Drupal, however, is a bit more complicated than just typing out an HTML anchor tag. It requires understanding how URLs are generated from routes, and how to define links as renderable arrays. It can also be tricky because of the multitude of deprecated, but still functioning, ways of creating links.

If you've ever created or edited a piece of content on a Drupal site you have already interacted with the Field API. The Field module (along with its user interface counterpart) is responsible for providing the forms and data components used to build up the content model that make up a Drupal site. Understanding how Drupal fields work and how they're constructed via the Field API is an important part of understanding how Drupal works.

Once we've explored the various field types provided by Drupal core, the next component of the Field API to explore is field widgets. Field widgets define how the data structure of the field is displayed on an edit form. When content editors interact with your field type they will be doing so via the field widget you provide. In this tutorial, we'll take a look at the field widgets provided by Drupal core, the plugin type required to define our own custom widget and how we can define multiple widget options for a single field type.

Field formatters are responsible for taking the data stored by a field and transforming it into what a vistor sees. We can define new field formatters to output data for new field types or to provide alternative formatting options for existing field types. Creating a field formatter plugin is a common task for Drupal developers.

In this tutorial we'll:

Many of the processes that Drupal performs when responding to a request are cached in order to increase performance. Creating the HTML for the page that a user sees or the JSON response to a REST request can require thousands of operations. Some operations are time consuming, memory heavy, CPU intense, or all 3. By performing the operation once, and then caching the result for next time, subsequent requests can be fulfilled faster. In order to make it easier to store, retrieve, and invalidate cached data, Drupal provides cache-related services you can use in your code.

Want to know if the person that's viewing your custom block is authenticated? Need to change the elements visible on the page based on a user's permissions or roles? Want to display a welcome message for users returning to your site?

All of these things require knowing who the user is that's currently accessing a page. This can be accomplished by using the current_user service to load an object that contains information about the current user as well as methods for checking permissions, and retrieving additional information.

In this tutorial we'll:

Understanding the flow--or life cycle--of a Drupal form will help you better understand how to build new forms or influence existing ones. This tutorial will help you understand the complete life cycle of a Drupal form: receiving the request from a browser, displaying a page with a form, rendering the form as HTML, handling the submitted form, validating input, handling errors, and processing data. We'll point out the common places that module developers might want to inject additional functionality into the process and link to tutorials with more details about how to do so.

Module developers can add new elements to a form by adding their definition to the $form array in the buildForm() method of their controller or via an implementation of hook_form_alter(). Doing so requires knowing the element #type, and details about any element-type-specific properties.

In this tutorial we'll:

When a form is submitted you'll need to check the data input by the user to ensure that it matches certain constraints, and to raise errors when necessary. Is the email address in the proper format? Is the title field long enough? Does the ASIN ID entered match a valid Amazon product? This process is called validation and is handled by a combination of the validateForm() method of a form controller, and validation callbacks.

In this tutorial we'll:

When working with forms that are not created by your code, where you're not implementing the form controller but rather interacting with the form via implementations of hook_form_alter(), you can use the #validate property of the root form element to add additional validation logic in the form of a callback function or method.

In this tutorial we'll:

You probably created a form with the intent of collecting user input and then doing something with that input. Using the submitForm() method of our form class we can access the validated, and sanitized, user input data and make use of it for our own needs. We might do things like save the collected data as configuration, update an entity, or use it as part of a search query.

In this tutorial we'll:

When you create a custom form for Drupal and your module defines the form controller, the best way to handle processing of submitted data is via the submitForm() method of your controller. This method is called automatically by the Form API during the process of handling a user-submitted form. It can be used to save incoming data to the database, trigger a workflow based on user input, and instruct the Form API where to send the user after form processing has completed.

In this tutorial we'll:

Forms are used for both collecting new data, and editing existing data. In order to allow users to modify existing data you need to pre-populate the elements on the form with the data you previously stored.

In this tutorial we'll look at the ways in which forms can be pre-populated with existing data, including:

Forms can be displayed as the main content of a route or by using the form_builder service to retrieve and display a form directly. Which one you choose will depend on where on the page you want the form to appear.

In this tutorial we'll:

• Go over the two different ways a form can be retrieved and displayed
• Demonstrate how to display a form inside a custom block using the form_builder service

By the end of this tutorial you'll know how to retrieve a form and have it rendered anywhere on the page.

A common use of Ajax is to alter a form by adding, removing, or updating parts of the form in response to actions taken by the user. The resulting altered form is still eventually submitted with a traditional HTTP POST request. For example, one might update the options available in a city dropdown field after someone has chosen a value in the country dropdown, or add an additional textfield for collecting a person's name when the user clicks an "Add another person" button.

In this tutorial we'll:

Deprecated code is any code flagged for future removal, but which has not yet been removed to ensure that existing code which relies on the to-be-removed code will continue to work. When an API, or feature, becomes deprecated it's a warning to all developers that at some point in the future this thing they are relying on will not exist, and they'll need to update their custom code to a new approach. Preferably before the existing one gets removed.

In this tutorial well:

As new major versions of Drupal are released, contributed modules need to be updated for compatibility. As of right now (October 2021) there are a lot of contributed modules with a Drupal 8 release and a patch in the queue to make them work with Drupal 9. However, there's no official Drupal 9 compatible release for the module, so the module can't be installed with Composer. This creates a circular problem where you can't composer require the module if you don't patch it, but you can't patch it until after it's been downloaded by Composer.