How do I use a template file for preparing HTML message body for emails?

Question

I want to use a template file for preparing the email message body using the table tag, and putting the submitted form data by user in table rows. I have implemented hook_mail() with the following code.

function get_price_mail($key, &$message, $params) {
  switch ($key) {
    case 'mail_to_eberhard':
      $message['headers']['Content-Type'] = 'text/html; charset=UTF-8; format=flowed; delsp=yes';
      $message['subject'] = t('Factory Purchase - ').\Drupal::config('system.site')->get('name');;
      $message['body'][] = $params['message'];
      break;
   }
}

I created a template file (get_price/templates/mail-to-eberhard.html.twig), but the message body is not using my template file.

How do I make Drupal 8 use my template file?

Answer 1

So here is the answer: Inside the hook theme function of your module use this code

function get_price_theme() {
  return [
    'mail_to_eberhard' => array (
        'template' => 'mail-to-eberhard',  // TWIG File
        'variables' => array('submitted_data'=>[]),
    ),
  ];
} 

where variables is the array of parameter you want to send to the template file. Now create a template file named as mail-to-eberhard.html.twig inside your modules template folder. Then inside the hook_mail() alter function use this code.

function get_price_mail($key, &$message, $params) {
  switch ($key) {
    case 'mail_to_eberhard':
      $message['headers']['Content-Type'] = 'text/html; charset=UTF-8; format=flowed; delsp=yes';
      //$message['from'] = \Drupal::config('system.site')->get('mail');
      $message['subject'] = t('Factory Purchase - ').\Drupal::config('system.site')->get('name');;
      //$message['subject'] = t('Article created: @title', array('@title' => $params['node_title']), $options);
      // Render the template to HTML
      // Set up email template
      $body_data = array (
         '#theme' => 'mail_to_eberhard',
         '#submitted_data' => $params['message']
      );
      //$message['body']['#theme'] = 'mail_to_eberhard';
      $message['body'][] = \Drupal::service('renderer')->render($body_data);
      break;
  }
} 

now inside you template file you can use the array variables like this

You have received one new message from the Get Price Tab.<br/><br/>
<b>Full Name</b> : {{ submitted_data['user_full_name'] }}<br/>
<b>Email</b> : {{ submitted_data['user_email'] }}<br/>
<b>Phone</b> : {{ submitted_data['user_number'] }}<br/>
<b>State</b> : {{ submitted_data['user_state'] }}<br/>
<b>Product SKU</b> : {{ submitted_data['product_sku'] }}<br/>
<b>Product URL</b> : <a href='{{ submitted_data['product_url'] }}'>{{ submitted_data['product_url'] }}</a>
<br/><b>Message</b> : {{ submitted_data['user_message'] }`