Lets code a module

mymodule.info

name = My Cool Module
description = Provides an area handler for views

core = 7.x

dependencies[] = views
dependencies[] = xautoload (>= 7.x-5.0)
						

mymodule.module

/**
 * Implements hook_views_api().
 */
function mymodule_views_api() {
  return [
    'api' => 3
  ];
}
						

mymodule.views.inc

/**
 * Implements hook_views_data().
 */
function mymodule_views_data() {
  return [
    'views' => [
      'mymodule_area' => [
        'title' => t('My Custom Area'),
        'help' => t('Adds a custom area handler.'),
        'area' => [
          'handler' => 'Drupal\mymodule\Views\Handlers\Area\MyCoolHandler'
        ]
      ]
    ]
  ];
}
						

Checkout our video on PSR4

Directory structure follows naming convention

namespace Drupal\mymodule\Views\Handlers\Area;

/**
 * Defines a new handler class for views.
 */
class MyCoolHandler {

}
						

Time to write a custom field.

We're going to create a psuedo field

'node' => [
  'my_custom_field' => [
    'title' => t('My Custom Field'),
    'help' => t('Showing how to write fields at SandCamp'),
    'real field' => 'created',
    'field' => [
      'handler' => 'Drupal\mymodule\Views\Handlers\Field\MyCustomField'
    ],
    'filter' => [
      'handler' => 'Drupal\mymodule\Views\Handlers\Filter\MyCustomFilter'
    ]
  ],
]
						

namespace Drupal\mymodule\Views\Handlers\Field;

class MyCustomField extends \views_handler_field {

  function render($values) {
    $value = $this->get_value($values);
    return date('Y-m-d', $value);
  }

}
						

Custom Filter

function option_definition() {
  $options = parent::option_definition();

  $options['even_odd'] = array('default' => 'odd');

  return $options;
}

function options_form(&$form, &$form_state) {
  $form['even_odd'] = [
    '#type' => 'radios',
    '#title' => t('Even or Odd'),
    '#default_value' => $this->options['even_odd'],
    '#options' => ['odd' => t('Only odd numbers'), 'even' => t('Just even numbers')],
    '#description' => t('Demonstrating how to create your own options form')
  ];

  parent::options_form($form, $form_state);
}

function admin_summary() {
  return $this->options['even_odd'] == 'even' ? t('Just even numbers') : t('Just odd numbers');
}
						

Change the query

function query() {
  $this->ensure_my_table();
  $operator = $this->options['even_odd'] == 'even' ? '=' : '>';
  $this->query->add_where_expression($this->options['group'], "($this->table_alias.$this->real_field % 2) $operator 0");
}