Configure Custom Backend Preview for Content Element

To allow editors a smoother experience, all custom content elements and plugins should be configured with a corresponding backend preview that shows an approximation of the element’s appearance in the TYPO3 page module. The following sections describe how to achieve that.

A PreviewRenderer is used to facilitate (record) previews in TYPO3.

The feature consists of two concepts:

  • PreviewRendererResolver which is a global implementation to detect which PreviewRenderer a given record needs.
  • PreviewRenderer which is the class responsible for generating the preview and the wrapping.

Writing a PreviewRenderer

A custom PreviewRenderer must implement the interface \TYPO3\CMS\Backend\Preview\PreviewRendererInterface which contains the following API methods:

/**
 * Dedicated method for rendering preview header HTML for
 * the page module only. Receives the the GridColumnItem
 * that contains the record for which a preview header
 * should be rendered and returned.
 *
 * @param GridColumnItem $item
 * @return string
 */
public function renderPageModulePreviewHeader(GridColumnItem $item): string;

/**
 * Dedicated method for rendering preview body HTML for
 * the page module only. Receives the the GridColumnItem
 * that contains the record for which a preview should be
 * rendered and returned.
 *
 * @param GridColumnItem $item
 * @return string
 */
public function renderPageModulePreviewContent(GridColumnItem $item): string;

/**
 * Render a footer for the record to display in page module below
 * the body of the item's preview.
 *
 * @param GridColumnItem $item
 * @return string
 */
public function renderPageModulePreviewFooter(GridColumnItem $item): string;

/**
 * Dedicated method for wrapping a preview header and body
 * HTML. Receives $item, an instance of GridColumnItem holding
 * among other things the record, which can be used to determine
 * appropriate wrapping.
 *
 * @param string $previewHeader
 * @param string $previewContent
 * @param GridColumnItem $item
 * @return string
 */
public function wrapPageModulePreview(string $previewHeader, string $previewContent, GridColumnItem $item): string;

Note

Further methods are expected to be added in the future to support generic preview rendering, e.g. usages outside PageLayoutView.

Implementing these methods allows you to control the exact composition of the preview.

This means assuming your PreviewRenderer returns <h4>Header</h4> from the header render method and <p>Body</p> from the preview content rendering method and your wrapping method does return '<div>' . $previewHeader . $previewContent . '</div>'; then the entire output becomes <div><h4>Header</h4><p>Body</p></div> when combined.

Should you wish to reuse parts of the default preview rendering and only change, for example, the method that renders the preview body content, you can subclass \TYPO3\CMS\Backend\Preview\StandardContentPreviewRenderer in your own PreviewRenderer class - and selectively override the methods from the API displayed above.

Configuring the implementation

Individual preview renderers can be defined by using one of the following two approaches:

$GLOBALS['TCA'][$table]['ctrl']['previewRenderer'] = My\PreviewRenderer::class;

This specifies the PreviewRenderer to be used for any record in $table.

Or if your table has a “type” field/attribute:

$GLOBALS['TCA'][$table]['types'][$type]['previewRenderer'] = My\PreviewRenderer::class;

This specifies the PreviewRenderer only for records of type $type as determined by the type field of your table.

Or finally, if your table and field have a subtype_value_field TCA setting (like tt_content.list_type for example) and you want to register a preview renderer that applies only when that value is selected (e.g. when a certain plugin type is selected and you can’t match it with the “type” of the record alone):

$GLOBALS['TCA'][$table]['types'][$type]['previewRenderer'][$subType] = My\PreviewRenderer::class;

Where $type is for example list (indicating a plugin) and $subType is the value of the list_type field when the type of plugin you want to target is selected as plugin type.

Note

The recommended location is in the ctrl array in your extension’s Configuration/TCA/$table.php or Configuration/TCA/Overrides/$table.php file. The former is used when your extension is the one that creates the table, the latter is used when you need to override TCA properties of tables added by the Core or other extensions.

Overriding the PreviewRendererResolver

If necessary, the PreviewRendererResolver can be overridden by setting:

$GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['backend']['previewRendererResolver'] = \TYPO3\CMS\Backend\Preview\StandardPreviewRendererResolver::class;

Once overridden, the old resolver will no longer be consulted.

\TYPO3\CMS\Backend\Preview\PreviewRendererResolverInterface must be implemented by PreviewRendererResolvers and contains a single API method, public function resolveRendererFor($table, array $row, int $pageUid); which needs to return a single PreviewRenderer based on the given input.