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Extending thumbnails

The thumbnails API enable you to easily choose an image for a specific content. If you do not want to use custom thumbnails, ContentType will be used instead.

Thumbnail mechanism

The thumbnail mechanism has two layers, and each layer can have many implementations. The mechanism checks if any of the implementations returns a field e.g. ezimage that has function "Can be a thumbnail" turned on.

If found, the image is used as a Content Type thumbnail.

First layer

First layer of the mechanism contains strategy pattern that focuses on finding a thumbnail source. The thumbnail can be found inside or outside the Content Type. For example for users thumbnails can be downloaded from an avatar-generating service.

For this layer there are following default implementations:

• The mechanism looks for Fields that can be thumbnail, if found, the mechanism moves to the second layer.
• If there are no Fields that can be a thumbnail, the Content Type icon will be used as a thumbnail.

Second layer

Second layer of mechanism enables selection of thumbnail from a Field that the first layer has found. It searches the Content Type for all the Fields e.g. images with function "Can be a thumbnail" turned on.

If there is more than one Field in the Content Type that can be used as a thumbnail, this layer will return the first nonempty Field as a thumbnail.

This mechanism can be modified to fit your site needs, so you can decide from where and how the thumbnails will be downloaded.

Create a thumbnail mechanism

First, create base strategy for returning custom thumbnails from a static file. Create StaticStrategy.php in src/Strategy.

<?php
​
declare(strict_types=1);
​
namespace App\Strategy;
​
use eZ\Publish\API\Repository\Values\Content\Thumbnail;
use eZ\Publish\API\Repository\Values\ContentType\ContentType;
use eZ\Publish\SPI\Repository\Strategy\ContentThumbnail\ThumbnailStrategy;
​
final class StaticStrategy implements ThumbnailStrategy
{
    /** @var string */
    private $staticThumbnail;
​
    public function __construct(string $staticThumbnail)
    {
        $this->staticThumbnail = $staticThumbnail;
    }
​
    public function getThumbnail(ContentType $contentType, array $fields): Thumbnail
    {
        return new Thumbnail([
            'resource' => $this->staticThumbnail,
        ]);
    }
}

Next, add the strategy with the ezplatform.spi.content.thumbnail_strategy tag and priority: 100 to config/services.yaml:

services:
    App\Strategy\StaticStrategy:
        arguments:
            $staticThumbnail: http://example.com/some_image.jpg
        tags:
            - { name: ezplatform.spi.content.thumbnail_strategy, priority: 100 }

Priority 100 will allow this strategy to be used first on a clean installation or before any other strategy with lower priority.

At this point you can go to the Back Office and check the results.

Other Fields as thumbnails

Any Field Type can generate a thumbnail, e.g.:

• DateAndTime (ezdatetime) - you can add a mini calendar thumbnail for Appointment Content Type and on the day of the appointment a clock thumbnail with a specific time when it takes place
• TextBlock (eztext) - you can add a first letter of the text block that is inside

Add eztext Field as thumbnail

First, create a strategy that will add support for eztext as the thumbnail. It will enable you to add a thumbnail URL in the text field.

Add FieldValueUrl.php in eZ/Thumbnails.

<?php
​
declare(strict_types=1);
​
namespace App\Thumbnails;
​
use eZ\Publish\API\Repository\Values\Content\Field;
use eZ\Publish\API\Repository\Values\Content\Thumbnail;
use eZ\Publish\SPI\Repository\Strategy\ContentThumbnail\Field\FieldTypeBasedThumbnailStrategy;
​
class FieldValueUrl implements FieldTypeBasedThumbnailStrategy
{
    public function getFieldTypeIdentifier(): string
    {
        return 'eztext';
    }

    public function getThumbnail(Field $field): ?Thumbnail
    {
        return new Thumbnail([
            'resource' => $field->value,
        ]);
    }
}

Next, add the strategy with the ezplatform.spi.field.thumbnail_strategy tag to config/services.yaml:

services:
    App\Thumbnails\FieldValueUrl:
        tags:
            - { name: ezplatform.spi.field.thumbnail_strategy }

At this point you can go to the Back Office and check the results.