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:

Hooks allow module developers to execute custom code at key moments during Drupal's request processing life cycle. They can be used to react to actions or conditions, alter forms and existing configuration, and extend Drupal in various ways. Knowing how to implement a hook is an essential skill for any Drupal developer.

In this tutorial we'll walk through the process of locating the documentation for a specific hook, and then implementing it. All hooks are implemented in the same way, so once you know how to implement one, you'll be able to implement any.

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:

As a module developer you should define and invoke new hooks in your module in order to allow other developers -- or even future you -- to extend your module's functionality without hacking your module's code. This requires:

• Creating a new, unique, name for your hook
• Providing documentation for your hook
• Invoking the hook at critical points in your code

By the end of this tutorial you should have a better idea of when to define a new hook and know how to invoke a hook from your code.

Drupal's Entity system provides several hooks that allow custom code to interact with various parts of the entity life cycle.

In this tutorial we'll:

• Examine the available hooks
• Learn how to make use of them to act on several different types of operations on individual entities

By the end if this tutorial you should have a better understanding of the hooks available to developers who want to respond to entity lifecycle operations and how to use them to customize the way specific entity types work.

On occasion you may need to modify the behavior of entity types defined by another module. Thankfully Drupal includes several alter hooks that can be used to override the behavior of another entity.

In this tutorial we will:

Drupal's Field API specifies the implementation details for field types, widgets and formatters. It also provides several hooks that allow custom code to alter these implementation details. In this tutorial we'll take a look at these Field API hooks and see how they can be used to change field types, widgets and formatters.

By the end of this lesson, you should be able to:

When determining which template file to use to theme an element, Drupal uses the list of theme hook suggestions to look for the best match. This allows for fine-grained control over how things appear based on dynamic state and contextual information in your application. The list of theme hook suggestions varies for each base template, so we need a way to figure out our options.

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:

Every row returned, from every source, during the execution of a migration is passed through hook_migrate_prepare_row() and hook_migrate_MIGRATION_ID_prepare_row(). Using these two hooks we can augment our migration in a variety of different ways.

In this tutorial we'll: