Plugins in Drupal 8 might sound as a new term for those who have not worked with pluggable entities like ctools in Drupal 7. As the name states Plug + in, its something that can be attached & removed easily, can fit into any context.
Drupal 8 has a nice ecosystem built around plugins now. Those intereseted in knowing more about Drupal 8 Plugin system, here is an interesting video from Drupalcon Portland:
In this article, we are going to talk about only one kind of Plugin which is Block. You couldn't place a block into multiple regions in Drupal 7(without using a contrib module). With blocks being pluggable now, this is solved right in the core.
For Drupal system to recognize a block, in Drupal 7 we had hook_block_info().This has been replaced with annotation-based discovery method in Drupal 8. Lets go through the porting process step by step. The major steps involved while writing a custom block plugin are as follows:
Directory Structure & where should the code be placed?:
Annotation Based Discovery:
Read the complete deabte & detail on why use annotation based-discovery & the performance gains: https://www.drupal.org/node/1882526.
Extending Blockbase Class:
With OOPs in Drupal8, there is a base class that core provides for creating a custom block plugin on top of it. Details on Api available at https://api.drupal.org/api/drupal/core!lib!Drupal!Core!Block!BlockBase.php/class/BlockBase/8
Setting Default Configuration:
Block Configuration Form:
Block render callback:
NOTE: Build function must return an array that can be passed to render function to generate HTML. You cannot renturn a static string from build function.