Create a custom link browser¶

In this tutorial we create a custom link browser and the associated backend link handler.

We create a new tab in the link browser window in the TYPO3 backend:

A custom link browser to link to GitHub issues¶

Tip

If you want to link to a record in a custom table, configure the RecordLinkBrowser. You do not need a custom link browser in that scenario.

We introduce a custom link format to store the links in this format: t3://github?issue=123.

This enables us to edit an existing link in the link browser or to change parts of the GitHub URI programmatically later.

And we render the new link in the frontend automatically.

Step by step to a custom link browser

1. Register the custom link browser tab in page TSconfig
2. Create a link browser tab
3. Introduce the custom link format
4. Render the custom link format in the frontend

1. Register the custom link browser tab in page TSconfig ¶

EXT:examples/Configuration/TsConfig/Page/LinkBrowser/GitHubLinkhandler.tsconfig¶

TCEMAIN.linkHandler {
   github {
      handler = T3docs\Examples\LinkHandler\GitHubLinkHandler
      label = LLL:EXT:examples/Resources/Private/Language/locallang_browse_links.xlf:github
      displayAfter = haiku
      scanBefore = url
      configuration {
         project = TYPO3-Documentation/TYPO3CMS-Reference-CoreApi
         action = issues
      }
   }
}

The following options are of note here:

handler: The backend link handler that we create in step 2.
configuration: Some configuration, available to the backend link handler. This information is not available in the frontend. Therefore in the frontend rendering of the link the information must be stored in another way. In this example we hardcoded it. But you could also make it available by TypoScript Setup or as part of the link that is saved.

For a complete list of available option see Link handler configuration.

2. Create a link browser tab ¶

To create a link browser tab we implement the interface \TYPO3\CMS\Backend\LinkHandler\LinkHandlerInterface.

All backend link handlers provided by the Core extend the abstract class TYPO3\CMS\Backend\LinkHandler\AbstractLinkHandler. However, this class is marked as @internal and therefore can be changed by the Core Team at any time.

You have the choice of implementing the LinkHandlerInterface yourself by having a look at the AbstractLinkHandler for best practices or to extend the AbstractLinkHandler. In the latter case your code might break on updates though.

In this tutorial, we implement the LinkHandlerInterface directly, as it is best practice not to rely on internal classes.

You can find the complete class in the extension EXT:examples on GitHub: GitHubLinkHandler.

We will explain some of the important methods below:

Initialization and dependencies ¶

Class T3docs\Examples\LinkHandler\GitHubLinkHandler¶

use TYPO3\CMS\Backend\Controller\AbstractLinkBrowserController;
use TYPO3\CMS\Core\Page\PageRenderer;
use TYPO3\CMS\Core\View\ViewInterface;

class GitHubLinkHandler implements LinkHandlerInterface
{
    protected array $linkAttributes = ['target', 'title', 'class', 'params', 'rel'];

    protected array $linkParts = [];

    protected ViewInterface $view;

    protected array $configuration;

    public function __construct(
        // The page renderer is needed to register the JavaScript
        private readonly PageRenderer $pageRenderer,
    ) {}

    public function initialize(AbstractLinkBrowserController $linkBrowser, $identifier, array $configuration)
    {
        $this->configuration = $configuration;
    }

    public function setView(ViewInterface $view): void
    {
        $this->view = $view;
    }
}

For technical reasons, not all dependencies needed by the backend link handler can be acquired by Dependency injection. Therefore the following two methods are called by Core classes once the dependencies are available:

LinkHandlerInterface::initialize() takes care of setting the \TYPO3\CMS\Backend\Controller\AbstractLinkBrowserController, the identifier and the configuration information. In this example we only need the configuration, the other parameters might be needed in different scenarios.

AbstractLinkBrowserController $linkBrowser: Is the surrounding class calling the link handler. This class stores configuration information of the complete link browser window.
string $identifier: Contains the key of the page TSconfig configuration of the link browser tab this instance renders.
array $configuration: Contains the page TSconfig configuration as array of the link browser tab this instance renders.

The method setView() is called by the AbstractLinkBrowserController once the view is available and contains the necessary information to render the link browser window.

Note

setView() is not part of the LinkHandlerInterface and its call is an implementation detail that might be changed in the future.

Enable dependency injection ¶

Backend link handlers are called internally in the TYPO3 Core by GeneralUtility::makeInstance(). Therefore dependency injection needs to be enabled by marking the class as public in the extension's Configuration/Services.yaml. As we keep internal states in the link handler class (for example $linkParts) it cannot be a singleton and must be marked as shared: false:

EXT:examples/Configuration/Services.yaml¶

services:
  _defaults:
    autowire: true
    autoconfigure: true
    public: false

  T3docs\Examples\LinkHandler\GitHubLinkHandler:
    public: true
    # The link handler keeps a state and can therefore be no singleton
    shared: false

Render the link browser tab ¶

The method LinkHandlerInterface::render() is called when the tab should be rendered. It registers the required JavaScript in the page renderer, assigns variables to the view and returns the rendered HTML.

Class T3docs\Examples\LinkHandler\GitHubLinkHandler¶

use Psr\Http\Message\ServerRequestInterface;

class GitHubLinkHandler implements LinkHandlerInterface
{
    public function render(ServerRequestInterface $request): string
    {
        $this->pageRenderer->loadJavaScriptModule('@t3docs/examples/github_link_handler.js');
        $this->view->assign('project', $this->configuration['project']);
        $this->view->assign('action', $this->configuration['action']);
        $this->view->assign('linkParts', $this->linkParts);
        $this->view->assign('issue', $this->linkParts['issue'] ?? '');

        return $this->view->render('LinkBrowser/GitHub');
    }
}

Set the link via JavaScript ¶

When the button in the rendered form is clicked to set a link, a custom JavaScript class interprets the form data and creates the link to be stored:

EXT:examples/Resources/Public/JavaScript/github_link_handler.js¶

/*
 * This file is part of the TYPO3 CMS project.
 *
 * It is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License, either version 2
 * of the License, or any later version.
 *
 * For the full copyright and license information, please read the
 * LICENSE.txt file that was distributed with this source code.
 *
 * The TYPO3 project - inspiring people to share!
 */

import LinkBrowser
     from "@typo3/backend/link-browser.js";

/**
 * Module: @t3docs/examples/github_link_handler.js
 * Github issue link interaction
 */

class GitHubLinkHandler {
     constructor() {
             var form_el = document.getElementById("lgithubform");
             form_el.addEventListener("submit", function(event) {
                     event.preventDefault();
                     var value = document.getElementById('lgithub').value;
                     if (value === 't3://github?issue=') {
                             return;
                     }
                     if (value.indexOf('t3://github?issue=') === 0) {
                             value = value.substring(18);
                     }
                     LinkBrowser.finalizeFunction('t3://github?issue=' + value);
             });
     }
}

export default new GitHubLinkHandler();

It is important that the JavaScript function calls LinkBrowser.finalizeFunction(). Otherwise no link will be set.

If not done yet, the JavaScript has to be registered in the file EXT:my_extension/Configuration/JavaScriptModules.php. Otherwise it will not be found by $pageRenderer->loadJavaScriptModule().

EXT:examples/Configuration/JavaScriptModules.php¶

<?php

return [
    'dependencies' => ['backend'],
    'imports' => [
        '@t3docs/examples/' => 'EXT:examples/Resources/Public/JavaScript/',
    ],
];

As our JavaScript class depends on classes provided by the backend system extension, backend has to be added as dependency. See also Loading ES6.

Can we handle this link?¶

The method LinkHandlerInterface::canHandleLink() is called when the user edits an existing link in the link browser. All backend link handlers will be called and can decide if they can handle that link. If so, they should store the provided information to be used in rendering (for example, to fill an input field with the old value).

Class T3docs\Examples\LinkHandler\GitHubLinkHandler¶

class GitHubLinkHandler implements LinkHandlerInterface
{
    public function canHandleLink(array $linkParts): bool
    {
        if ($linkParts['type'] !== 'github') {
            return false;
        }
        $this->linkParts = $linkParts['url']??[];
        return true;
    }
}

Format current URL ¶

The function LinkHandlerInterface::formatCurrentUrl() is used to preview what the link will look like in the backend, for example, in the upper part of the link browser window.

Attention

LinkHandlerInterface::formatCurrentUrl() is not used to render the link in the frontend.

3. Introduce the custom link format ¶

You can find the complete class in the extension EXT:examples on GitHub: GitHubLinkHandling.

Our backend link handler implementation from step 1 saves the link in the custom format t3://github?issue=123 via JavaScript.

This format is only an arbitrary string until we tell TYPO3 how to handle links of the new format by a second class which implements the TYPO3\CMS\Core\LinkHandling\LinkHandlingInterface.

Note

There are two interfaces with very similar names and very different functionality involved here. The \TYPO3\CMS\Backend\LinkHandler\LinkHandlerInterface renders a tab in the link browser window in the backend. Its implementing class is commonly called a "(backend) link handler". Classes implementing the interface TYPO3\CMS\Core\LinkHandling\LinkHandlingInterface handle the introduced link format. Such a class is called a "(core) link handler".

Class T3docs\Examples\LinkHandler\GitHubLinkHandling¶

/**
 * Resolves GitHub Links
 */
class GitHubLinkHandling implements LinkHandlingInterface
{
    protected $baseUrn = 't3://github';

    public function asString(array $parameters): string
    {
        $githubIssue = (int)$parameters['issue'];
        return $this->baseUrn . '?issue=' . $githubIssue;
    }

    public function resolveHandlerData(array $data): array
    {
        return [
            'issue' => (int)$data['issue'],
        ];
    }
}

The method LinkHandlingInterface::asString() creates a string representation from the parameter array.

LinkHandlingInterface::resolveHandlerData() receives the string representation of the link and creates the parameter array from it. For convenience the parameters are already parsed and stored as key-value pairs in an array for you. You can perform further processing here if needed.

4. Render the custom link format in the frontend ¶

The link builder, a class extending the abstract class \TYPO3\CMS\Frontend\Typolink\AbstractTypolinkBuilder is called whenever a link is rendered in the frontend, for example via TypoScript .typolink, by the \TYPO3\CMS\Frontend\ContentObject\ContentObjectRenderer::typoLink function or by the \TYPO3\CMS\Extbase\Mvc\Web\Routing\UriBuilder.

Class T3docs\Examples\LinkHandler\GithubLinkBuilder¶

use TYPO3\CMS\Frontend\Typolink\LinkResult;
use TYPO3\CMS\Frontend\Typolink\LinkResultInterface;
use TYPO3\CMS\Frontend\Typolink\UnableToLinkException;

/**
 * Builds a TypoLink to a Github issue
 */
class GithubLinkBuilder extends AbstractTypolinkBuilder
{
    private const TYPE_GITHUB = 'github';

    public function build(
        array &$linkDetails,
        string $linkText,
        string $target,
        array $conf
    ): LinkResultInterface {
        $issueId = (int)$linkDetails['issue'];
        if ($issueId < 1) {
            throw new UnableToLinkException(
                '"' . $issueId . '" is not a valid GitHub issue number.',
                // Use the Unix timestamp of the time of creation of this message
                1665304602,
                null,
                $linkText
            );
        }
        $url = 'https://github.com/TYPO3-Documentation/TYPO3CMS-Reference-CoreApi/issues/' . $issueId;

        return (new LinkResult(self::TYPE_GITHUB, $url))
            ->withTarget($target)
            ->withLinkConfiguration($conf)
            ->withLinkText($linkText);
    }
}

The link builder must be registered in ext_localconf.php, so that the correct link builder for the new type can be determined by the calling API:

EXT:examples/ext_localconf.php (Excerpt)¶

$GLOBALS['TYPO3_CONF_VARS']['FE']['typolinkBuilder']['github'] =
    \T3docs\Examples\LinkHandler\GithubLinkBuilder::class;

The function AbstractTypolinkBuilder::build() is called with the link configuration and data from the typolink function. If the link can be rendered, it returns a new \TYPO3\CMS\Frontend\Typolink\LinkResultInterface. The actual rendering of the link depends on the context the link is rendered in (for example HTML or JSON).

If the link cannot be built it should throw a \TYPO3\CMS\Frontend\Typolink\UnableToLinkException.

Attention

The configuration from the page TSconfig configuration (step 1) is not available in the frontend. Therefore the information which repository to use must be stored in another way. In this example we hardcoded it. But you could also make it available by TypoScript setup or as part of the link format that is saved.