To complete the implementation, we must register our FieldType with Symfony, by creating a service for it.
Services are by default declared by bundles in Resources/config/services.yml.
Using a dedicated file for the FieldType services
In order to be closer with the kernel best practices, we could declare our FieldType services in a custom fieldtypes.yml file.
All we have to do is instruct the bundle to actually load this file in addition to services.yml (or instead of services.yml !). This is done in the extension definition file, DependencyInjection/EzSystemsTweetFieldTypeExtension.php, in the load() method.
Inside this file, file, find this line:
This is where our bundle tells Symfony that when parameters are loaded, services.yml should be loaded from Resources/config/ (defined above). Either replace edit the line, or add a new one with:
Like most API components, FieldTypes use the Symfony 2 service tag mechanism.
The principle is quite simple: a service can be assigned one or several tags, with specific parameters. When the dependency injection container is compiled into a PHP file, tags are read by CompilerPass implementations that add extra handling for tagged services.
For FieldTypes, each service tagged as ezpublish.fieldType is added to a registry using the alias argument as its unique identifier (ezstring, ezxmltext…). Each FieldType must also inherit from the abstract ezpublish.fieldType service. This ensures that the initialization steps shared by all fieldtypes are executed.
Here is the service definition for our Tweet type:
Resources/config/services.yml
We take care of namespacing our fieldtype with our vendor and bundle name to limit the risk of naming conflicts.