TYPO3: Render a backend preview of custom content elements (TYPO3 CMS 6.2)

ext_localconf.php

<?php

// configure your custom content elements here
// ...

// add hook
// http://docs.typo3.org/typo3cms/CoreApiReference/ApiOverview/Hooks/Configuration/Index.html#hooks-core
$GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['cms/layout/class.tx_cms_layout.php']['tt_content_drawItem'][$_EXTKEY] = t3lib_extMgm::extPath($_EXTKEY) . 'Classes/Hooks/PageLayoutView.php:\Your\Extension\Namespace\Hooks\PageLayoutView';

PageLayoutView.php

<?php

namespace Your\Extension\Namespace\Hooks;

class PageLayoutView implements \TYPO3\CMS\Backend\View\PageLayoutViewDrawItemHookInterface
{

    /**
     * Preprocesses the preview rendering of a content element.
     *
     * @param  \TYPO3\CMS\Backend\View\PageLayoutView $parentObject  Calling parent object
     * @param  boolean                                $drawItem      Whether to draw the item using the default functionalities
     * @param  string                                 $headerContent Header content
     * @param  string                                 $itemContent   Item content
     * @param  array                                  $row           Record row of tt_content
     * @return void
     */
    public function preProcess(\TYPO3\CMS\Backend\View\PageLayoutView &$parentObject, &$drawItem, &$headerContent, &$itemContent, array &$row)
    {
        switch ($row['CType']) {

         // sample
        case 'yourextension_quote':
            $drawItem = false;
            $headerContent = '<strong>' . $parentObject->CType_labels[$row['CType']] . '</strong><br/>';
            $itemContent = $row['tx_yourextension_quote'] . '<br/>';
            break;

         // sample using an extbase repository
        case 'yourextension_teaser':
            $drawItem = false;
            $headerContent = '<strong>' . $parentObject->CType_labels[$row['CType']] . '</strong><br/>';
            $extbaseObjectManager = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance('TYPO3\\CMS\\Extbase\\Object\\ObjectManager');
            $yourRepository = $extbaseObjectManager->get('\Your\Extension\Namespace\Domain\Repository\YourRepository');
            $elements = $yourRepository->findByUid($row['uid']);
            foreach ($elements as $element) {
                $itemContent .= $element->getTitle() . '<br/>';
            }
            break;

        }

    }

}