Creating Forms with the Form API | Drupal 8 Development Cookbook

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Drupal 8 Development Cookbook

By : Matt Glaman

4.7 (3)

Drupal 8 Development Cookbook

4.7 (3)

By: Matt Glaman

Overview of this book

Began as a message board, Drupal today is open source software maintained and developed by a community of over 1,000,000 users and developers. Drupal is used by numerous local businesses to global corporations and diverse organizations all across the globe. With Drupal 8’s exciting features it brings, this book will be your go-to guide to experimenting with all of these features through helpful recipes. We’ll start by showing you how to customize and configure the Drupal environment as per your requirements, as well as how to install third-party libraries and then use them in the Drupal environment. Then we will move on to creating blocks and custom modules with the help of libraries. We will show you how to use the latest mobile-first feature of Drupal 8, which will help you make your apps responsive across all the major platforms. This book will also show you how to incorporate multilingual facilities in your sites, use web services and third-party plugins with your applications from inside Drupal 8, and test and deploy your apps.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Sections

Conventions

Reader feedback

Customer support

Free Chapter

Up and Running with Drupal 8

Up and Running with Drupal 8

Introduction

Installing Drupal

Using a distribution with Drupal

Installing modules and themes

Using multisites in Drupal 8

Tools for setting up an environment

Running tests - Simpletest and PHPUnit

The Content Authoring Experience

The Content Authoring Experience

Introduction

Configuring the WYSIWYG editor

Adding and editing content

Creating a menu and linking content

Providing inline editing

Creating a custom content type

Applying new Drupal 8 core field types

Customizing the form display of a node

Customizing the display output of a node

Displaying Content through Views

Displaying Content through Views

Introduction

Listing content

Editing the default admin interfaces

Creating a block from a View

Utilizing dynamic arguments

Adding a relationship in a View

Providing an Entity Reference result View

Extending Drupal

Extending Drupal

Introduction

Creating a module

Defining a custom page

Defining permissions

Providing the configuration on the installation or update

Creating an event subscriber

Using Features 3.0

Frontend for the Win

Frontend for the Win

Introduction

Creating a custom theme based on Classy

Using the new asset management system

Twig templating

Using the Breakpoint module

Using the Responsive Image module

Creating Forms with the Form API

Creating Forms with the Form API

Introduction

Creating a form

Using new HTML5 elements

Validating form data

Processing submitted form data

Altering other forms

Plug and Play with Plugins

Plug and Play with Plugins

Introduction

Creating blocks using plugins

Creating a custom field type

Creating a custom field widget

Creating a custom field formatter

Creating a custom plugin type

Multilingual and Internationalization

Multilingual and Internationalization

Introduction

Translating administrative interfaces

Translating configuration

Translating content

Creating multilingual views

Configuration Management - Deploying in Drupal 8

Configuration Management - Deploying in Drupal 8

Introduction

Importing and exporting configurations

Synchronizing site configurations

Using command-line workflow processes

Updating and installing new module configurations

The Entity API

The Entity API

Introduction

Creating a configuration entity type

Creating a content entity type

Creating a bundle for a content entity type

Implementing custom access control for an entity

Providing a custom storage handler

Creating a route provider

Off the Drupalicon Island

Off the Drupalicon Island

Introduction

Implementing and using a third-party JavaScript library

Implementing and using a third-party CSS library

Implementing and using a third-party PHP library

Web Services

Web Services

Introduction

Enabling RESTful interfaces

Using POST to create data

Using PATCH to update data

Using Views to provide custom data sources

Authentication

Using JSON API

The Drupal CLI

The Drupal CLI

Introduction

Rebuilding cache in Drupal Console or Drush

Using Drush to interact with the database

Using Drush to manage users

Scaffolding code through Console

Making a Drush command

Making a Console command

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Validating form data

All forms must implement the \Drupal\Core\Form\FormInterface. The interface defines a validation method. The validateForm method is invoked once a form has been submitted and provides a way to validate the data and halt the processing of the data if required. The form state object provides methods for marking specific fields as having the error, providing a user experience tool to alert your users to specify the problem input.

In this recipe, we will be validating the length of the submitted field.

Getting ready

This recipe will use the module and custom form created in the first Creating a form recipe.

How to do it...

Open and edit the \Drupal\drupalform\Form\ExampleForm class in the src/Form directory of the module.

Before validating the company_name value, we will need to check whether the value is empty using the isValueEmpty() method from the \Drupal\Core\Form\FormStateInterface object:

/** 
 * {@inheritdoc} 
 */ 
public function validateForm(array &$form,  FormStateInterface...

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