Can't pass variable to views style plugin template

Question

How do I pass a variable to a twig template from a preprocess function of a views style plugin in a custom module?

In alpha.module, I have tried:

function alpha_preprocess_views_view(&$variables) {
  $variables["beta"] = "1";
}

and

function alpha_preprocess_page(&$variables) {
  $variables["beta"] = "1";
}

The template file is alpha-gamma.html.twig and the plugin is Gamma.php:

/**
* Style plugin.
*
* @ViewsStyle(
*   id = "gamma",
*   title = @Translation("Gamma"),
*   help = @Translation("Displays gamma."),
*   theme = "alpha_gamma",
*   display_types = {"normal"}
* )
*/
class Gamma extends StylePluginBase {
...
}

The template file is invoked and renders its output on the view's row results. However, {{ beta }} yields no result in the same file. I know I'm missing something important, but none of the examples I've found are specific to this type of row style template.

Guidance would be appreciated!

Answer 1

In below code you preprocess the variables for views-view.html.twig file

function alpha_preprocess_views_view(&$variables) {
  $variables["beta"] = "1";
}

and, function alpha_preprocess_page(&$variables) will preprocess the variables for page.html.twig

So, if you create a file views-view.html.twig then you will get your variable {{ beta }}