protected function sortMenu()
	{
		if ($GLOBALS['TL_DCA'][$this->strTable]['list']['sorting']['mode'] != 2 && $GLOBALS['TL_DCA'][$this->strTable]['list']['sorting']['mode'] != 4)
		{
			return '';
		}

		$sortingFields = array();

		// Get sorting fields
		foreach ($GLOBALS['TL_DCA'][$this->strTable]['fields'] as $k=>$v)
		{
			if ($v['sorting'])
			{
				$sortingFields[] = $k;
			}
		}

		// Return if there are no sorting fields
		if (empty($sortingFields))
		{
			return '';
		}

		/** @var AttributeBagInterface $objSessionBag */
		$objSessionBag = System::getContainer()->get('session')->getBag('contao_backend');

		$session = $objSessionBag->all();
		$orderBy = $GLOBALS['TL_DCA'][$this->strTable]['list']['sorting']['fields'];
		$firstOrderBy = preg_replace('/\s+.*$/', '', $orderBy[0]);

		// Add PID to order fields
		if ($GLOBALS['TL_DCA'][$this->strTable]['list']['sorting']['mode'] == 3 && $this->Database->fieldExists('pid', $this->strTable))
		{
			array_unshift($orderBy, 'pid');
		}

		// Set sorting from user input
		if (Input::post('FORM_SUBMIT') == 'tl_filters')
		{
			$strSort = Input::post('tl_sort');

			// Validate the user input (thanks to aulmn) (see #4971)
			if (\in_array($strSort, $sortingFields, true))
			{
				$session['sorting'][$this->strTable] = \in_array($GLOBALS['TL_DCA'][$this->strTable]['fields'][$strSort]['flag'], array(2, 4, 6, 8, 10, 12)) ? "$strSort DESC" : $strSort;
				$objSessionBag->replace($session);
			}
		}

		// Overwrite the "orderBy" value with the session value
		elseif (\strlen($session['sorting'][$this->strTable]))
		{
			$overwrite = preg_quote(preg_replace('/\s+.*$/', '', $session['sorting'][$this->strTable]), '/');
			$orderBy = array_diff($orderBy, preg_grep('/^'.$overwrite.'/i', $orderBy));

			array_unshift($orderBy, $session['sorting'][$this->strTable]);

			$this->firstOrderBy = $overwrite;
			$this->orderBy = $orderBy;
		}

		$options_sorter = array();

		// Sorting fields
		foreach ($sortingFields as $field)
		{
			$options_label = \strlen(($lbl = \is_array($GLOBALS['TL_DCA'][$this->strTable]['fields'][$field]['label']) ? $GLOBALS['TL_DCA'][$this->strTable]['fields'][$field]['label'][0] : $GLOBALS['TL_DCA'][$this->strTable]['fields'][$field]['label'])) ? $lbl : $GLOBALS['TL_LANG']['MSC'][$field];

			if (\is_array($options_label))
			{
				$options_label = $options_label[0];
			}

			$options_sorter[$options_label] = '  <option value="'.StringUtil::specialchars($field).'"'.(((!\strlen($session['sorting'][$this->strTable]) && $field == $firstOrderBy) || $field == str_replace(' DESC', '', $session['sorting'][$this->strTable])) ? ' selected="selected"' : '').'>'.$options_label.'</option>';
		}

		// Sort by option values
		uksort($options_sorter, 'strcasecmp');

		return '
<div class="tl_sorting tl_subpanel">
<strong>' . $GLOBALS['TL_LANG']['MSC']['sortBy'] . ':</strong>
<select name="tl_sort" id="tl_sort" class="tl_select">
'.implode("\n", $options_sorter).'
</select>
</div>';
	}
protected function sortMenu()
	{
		if ($GLOBALS['TL_DCA'][$this->strTable]['list']['sorting']['mode'] != 2 && $GLOBALS['TL_DCA'][$this->strTable]['list']['sorting']['mode'] != 4)
		{
			return '';
		}

		$sortingFields = array();

		// Get sorting fields
		foreach ($GLOBALS['TL_DCA'][$this->strTable]['fields'] as $k=>$v)
		{
			if ($v['sorting'])
			{
				$sortingFields[] = $k;
			}
		}

		// Return if there are no sorting fields
		if (empty($sortingFields))
		{
			return '';
		}

		/** @var AttributeBagInterface $objSessionBag */
		$objSessionBag = System::getContainer()->get('session')->getBag('contao_backend');

		$session = $objSessionBag->all();
		$orderBy = $GLOBALS['TL_DCA'][$this->strTable]['list']['sorting']['fields'];
		$firstOrderBy = preg_replace('/\s+.*$/', '', $orderBy[0]);

		// Add PID to order fields
		if ($GLOBALS['TL_DCA'][$this->strTable]['list']['sorting']['mode'] == 3 && $this->Database->fieldExists('pid', $this->strTable))
		{
			array_unshift($orderBy, 'pid');
		}

		// Set sorting from user input
		if (Input::post('FORM_SUBMIT') == 'tl_filters')
		{
			$strSort = Input::post('tl_sort');

			// Validate the user input (thanks to aulmn) (see #4971)
			if (\in_array($strSort, $sortingFields, true))
			{
				$session['sorting'][$this->strTable] = \in_array($GLOBALS['TL_DCA'][$this->strTable]['fields'][$strSort]['flag'], array(2, 4, 6, 8, 10, 12)) ? "$strSort DESC" : $strSort;
				$objSessionBag->replace($session);
			}
		}

		// Overwrite the "orderBy" value with the session value
		elseif (\strlen($session['sorting'][$this->strTable]))
		{
			$overwrite = preg_quote(preg_replace('/\s+.*$/', '', $session['sorting'][$this->strTable]), '/');
			$orderBy = array_diff($orderBy, preg_grep('/^'.$overwrite.'/i', $orderBy));

			array_unshift($orderBy, $session['sorting'][$this->strTable]);

			$this->firstOrderBy = $overwrite;
			$this->orderBy = $orderBy;
		}

		$options_sorter = array();

		// Sorting fields
		foreach ($sortingFields as $field)
		{
			$options_label = \strlen(($lbl = \is_array($GLOBALS['TL_DCA'][$this->strTable]['fields'][$field]['label']) ? $GLOBALS['TL_DCA'][$this->strTable]['fields'][$field]['label'][0] : $GLOBALS['TL_DCA'][$this->strTable]['fields'][$field]['label'])) ? $lbl : $GLOBALS['TL_LANG']['MSC'][$field];

			if (\is_array($options_label))
			{
				$options_label = $options_label[0];
			}

			$options_sorter[$options_label] = '  <option value="'.StringUtil::specialchars($field).'"'.(((!\strlen($session['sorting'][$this->strTable]) && $field == $firstOrderBy) || $field == str_replace(' DESC', '', $session['sorting'][$this->strTable])) ? ' selected="selected"' : '').'>'.$options_label.'</option>';
		}

		// Sort by option values
		uksort($options_sorter, 'strcasecmp');

		return '
<div class="tl_sorting tl_subpanel">
<strong>' . $GLOBALS['TL_LANG']['MSC']['sortBy'] . ':</strong>
<select name="tl_sort" id="tl_sort" class="tl_select">
'.implode("\n", $options_sorter).'
</select>
</div>';
	}
Return a select menu that allows to sort results by a particular field

@return string