Hook a twig template to a block in Drupal 8 - drupal-8

Question

I created a module which creates a custom block :
<?php
/**
* Provides a 'SLS Block' Block
*
* #Block(
* id = "SLS-Subheader",
* admin_label = #Translation("SLS Subheader"),
* )
*/
namespace Drupal\subheader\Plugin\Block;
use Drupal\Core\Block\BlockBase;
class SubheaderBlock extends BlockBase {
/**
* {#inheritdoc}
*/
public function build() {
return array(
'#title' => "test",
);
}
}
?>
The module name is "subheader"
In my subheader.module i want to hook a specific template:
<?php
/**
* Implements hook_theme().
*/
function subheader_theme() {
return array(
'slssubheader' => array(
'variables' => array('pierre' => NULL),
'template' => 'specifictemplate',
),
);
}
I tried all kind of naming convention for the function name and the array key, but always unsuccesful. It never hook the template to specifictemplate.html.twig
Anyone has an idea??
Thanks a LOOOOTTT
Pierre

Answer 1

I had the same problem, though probably a different cause. Google lead me to your question though. The issue with your code is the missing #theme key in your build method I believe:
public function build() {
return array(
'#title' => "test",
'#theme' => 'slssubheader' // this one
);
}
In my case I had to search for a couple of hours before I found out I accidentally added a custom namespace to my .module file. Drupal doesn't like that and didn't recognize any of my hooks.