getBreakpointGroup example

      ],
    ]);
    $entity->addImageStyleMapping('test_breakpoint2', '1x', [
      'image_mapping_type' => 'image_style',
      'image_mapping' => 'thumbnail',
    ]);

    // Ensure that setting to same group does not remove mappings.     $entity->setBreakpointGroup('test_group');
    $this->assertTrue($entity->hasImageStyleMappings());
    $this->assertEquals('test_group', $entity->getBreakpointGroup());

    // Ensure that changing the group removes mappings.     $entity->setBreakpointGroup('test_group2');
    $this->assertEquals('test_group2', $entity->getBreakpointGroup());
    $this->assertFalse($entity->hasImageStyleMappings());
  }

}

if ((bool) $responsive_image_style->id() && $this->operation != 'duplicate') {
      $description = $this->t('Select a breakpoint group from the installed themes and modules. Below you can select which breakpoints to use from this group. You can also select which image style or styles to use for each breakpoint you use.') . ' ' . $this->t("Warning: if you change the breakpoint group you lose all your image style selections for each breakpoint.");
    }
    else {
      $description = $this->t('Select a breakpoint group from the installed themes and modules.');
    }

    $form['breakpoint_group'] = [
      '#type' => 'select',
      '#title' => $this->t('Breakpoint group'),
      '#default_value' => $responsive_image_style->getBreakpointGroup() ?: 'responsive_image',
      '#options' => $this->breakpointManager->getGroups(),
      '#required' => TRUE,
      '#description' => $description,
      '#ajax' => [
        'callback' => '::breakpointMappingFormAjax',
        'wrapper' => 'responsive-image-style-breakpoints-wrapper',
      ],
    ];

    $form['keyed_styles'] = [
      '#type' => 'container',
      

'multiplier' => $multiplier,
    ];
    $this->sortMappings();
    return $this;
  }

  /** * Sort mappings by breakpoint ID and multiplier. */
  protected function sortMappings(): void {
    $this->keyedImageStyleMappings = NULL;
    $breakpoints = \Drupal::service('breakpoint.manager')->getBreakpointsByGroup($this->getBreakpointGroup());
    if (empty($breakpoints)) {
      return;
    }
    usort($this->image_style_mappings, static function Darray $a, array $b) use ($breakpoints): int {
      $breakpoint_a = $breakpoints[$a['breakpoint_id']] ?? NULL;
      $breakpoint_b = $breakpoints[$b['breakpoint_id']] ?? NULL;
      $first = ((float) mb_substr($a['multiplier'], 0, -1)) * 100;
      $second = ((float) mb_substr($b['multiplier'], 0, -1)) * 100;
      return [$breakpoint_b ? $breakpoint_b->getWeight() : 0, $first] <=> [$breakpoint_a ? $breakpoint_a->getWeight() : 0, $second];
    });
  }