templateDetails.xml

The templateDetails.xml is the file that defines the installation instructions, the module positions and the style form for the template. The sections are defined as:

<?xml version="1.0" encoding="UTF-8"?>
<extension type="template" client="site">
	<name><!-- Name of the template go here --></name>
	<version><!-- Version of the template go here --></version>
	<creationDate><!-- Date of creation of the template go here --></creationDate>
	<author><!-- Author's name of the template go here --></author>
	<authorEmail><!-- Author's email of the template go here --></authorEmail>
	<copyright>><!-- Copyright of the template go here --></copyright>
	<description><!-- Description of the template go here --></description>
  <namespace><!-- Description of the template go here, usually CompanyNamespace\Templates\Templatename --></namespace>
	<inheritable>1</inheritable>
	<files><!-- Files/Folders for the template folder entries go here --></files>
	<media destination="templates/site/cassiopeia" folder="media"><!-- Folders for the static assets entries go here --></media>
	<positions><!-- Positions entries go here --></positions>
	<languages folder="language"><!-- Languages entries go here --></languages>
	<config>
		<fields name="params">
			<fieldset name="advanced"><!-- Fields definitions go here --></fieldset>
		</fields>
	</config>
</extension>

Since 5.1 in the config section the Menu Assignement tab can be overriden through the config part of the templateDetails.xml. So an example entry as the following will override the Menu Assignement tab contents with a field named menus:

<fields name="assigned">
  <fieldset name="assigned" addfieldprefix="YourNamespace\Templates\Field">
    <field name="assigned" type="menus" />
  </fieldset>
</fields>

A sample code for the field menus follows:

templates/templateName/src/Field/MenusField.php

<?php
namespace YourNamespace\Templates\Field;

use Joomla\CMS\Factory;
use Joomla\CMS\Form\Field\TextField;
use Joomla\CMS\Language\Text;
use Joomla\CMS\Layout\LayoutHelper;
use Joomla\Component\Menus\Administrator\Helper\MenusHelper;


// phpcs:disable PSR1.Files.SideEffects
\defined('_JEXEC') or die;
// phpcs:enable PSR1.Files.SideEffects


class MenusField extends TextField
{
    protected $type = 'Menus';

    public function setup(\SimpleXMLElement $element, $value, $group = null)
    {
        // Make sure there is a valid FormField XML element.
        if ((string) $element->getName() !== 'field'){
            return false;
        }

        // Reset the input and label values.
        $this->input = null;
        $this->label = null;

        // Set the XML element object.
        $this->element = $element;

        // Set the group of the field.
        $this->group = $group;

        $attributes = [
        'multiple', 'name', 'id', 'hint', 'class', 'description', 'labelclass', 'onchange', 'onclick', 'validate', 'pattern', 'validationtext',
        'default', 'required', 'disabled', 'readonly', 'autofocus', 'hidden', 'autocomplete', 'spellcheck', 'translateHint', 'translateLabel',
        'translate_label', 'translateDescription', 'translate_description', 'size', 'showon'];

        $this->default = isset($element['value']) ? (string) $element['value'] : $this->default;

        // Set the field default value.
        $this->value = $value;

        // Lets detect miscellaneous data attribute. For eg, data-*
        foreach ($this->element->attributes() as $key => $value) {
            if (strpos($key, 'data-') === 0) {
                // Data attribute key value pair
                $this->dataAttributes[$key] = $value;
            }
        }

        foreach ($attributes as $attributeName) {
            $this->__set($attributeName, $element[$attributeName]);
        }

        // Allow for repeatable elements
        // $repeat = (string) $element['repeat'];
        // $this->repeat = ($repeat === 'true' || $repeat === 'multiple' || (!empty($this->form->repeat) && $this->form->repeat == 1));

        // Set the visibility.
        $this->hidden = ($this->hidden || strtolower((string) $this->element['type']) === 'hidden');

        $this->parentclass = isset($this->element['parentclass']) ? (string) $this->element['parentclass'] : $this->parentclass;

        // Add required to class list if field is required.
        if ($this->required) {
            $this->class = trim($this->class . ' required');
        }

        // Hide the label
        $this->hiddenLabel = true;
        $this->hidden = true;

        return true;
    }

    public function getInput() {
        // Initialise related data.
        $menuTypes = MenusHelper::getMenuLinks();
        $user      = $this->getCurrentUser();
        $app       = Factory::getApplication();
        $currentId = $app->input->getInt('id');

        /** @var Joomla\CMS\WebAsset\WebAssetManager $wa */
        $wa = Factory::getApplication()->getDocument()->getWebAssetManager();
        $wa->useScript('com_templates.admin-template-toggle-assignment');

        $html = '<label id="jform_menuselect-lbl" for="jform_menuselect">'. Text::_('JGLOBAL_MENU_SELECTION') . '</label>'
        .  '<div class="btn-toolbar">'
        .    '<button class="btn btn-sm btn-secondary jform-rightbtn" type="button" onclick="Joomla.toggleAll()">'
        .    '<span class="icon-square" aria-hidden="true"></span> ' . Text::_('JGLOBAL_SELECTION_INVERT_ALL') . '</button>'
        .  '</div>'
        .  '<div id="menu-assignment" class="menu-assignment">'
        .    '<ul class="menu-links">';

        foreach ($menuTypes as &$type) {
            $html .= '<li>'
            . '<div class="menu-links-block">'
            .   '<button class="btn btn-sm btn-secondary jform-rightbtn mb-2" type="button" onclick=\'Joomla.toggleMenutype("' . $type->menutype . '")\'>'
            .   '<span class="icon-square" aria-hidden="true"></span> ' . Text::_('JGLOBAL_SELECTION_INVERT') . '</button>'
            .   '<h5>' . $type->title ?: $type->menutype . '</h5>';

            foreach ($type->links as $link) {
                $html .= '<label class="checkbox small" for="link' . (int) $link->value . '" >'
                . '<input type="checkbox" name="jform[assigned][]" value="'
                . (int) $link->value . '" id="link' . (int) $link->value . '"'
                . (($link->template_style_id == $currentId) ? ' checked="checked"' : '')
                . (($link->checked_out && $link->checked_out != $user->id) ? ' disabled="disabled"' : ' class="form-check-input chk-menulink menutype-' . $type->menutype . '"')
                . '/>';

                $html .= LayoutHelper::render('joomla.html.treeprefix', ['level' => $link->level]) . $link->text;
                $html .='</label>';
            }

            $html .= '</div></li>';
        }

        $html .= '</ul></div>';

        return $html;
    }
}