How to change theme programmatically for specific controller in magento 2?

Question

In magento 1.X we can change theme programmatically in controller action by below code :

Mage::getDesign()->setArea('frontend') //Area (frontend|adminhtml)
    ->setPackageName('packagename') //Name of Package
    ->setTheme('default');// Name of theme

How to change theme programmatically for specific controller in magento 2 ?

Answer 1

After digging the code I found the solution.

Write below code at the starting of your controller's action execute function's body.

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$objectManager->get(\Magento\Framework\View\DesignInterface::class)->setDesignTheme('Magento/luma', 'frontend');

For example :

public function execute()
    {

        $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
        $objectManager->get(\Magento\Framework\View\DesignInterface::class)->setDesignTheme('Magento/luma', 'frontend');

        $post = $this->initModel();

        if (!$post) {
            throw new NotFoundException(__('Page not found'));
            die;
        }

        /* @var \Magento\Backend\Model\View\Result\Page $resultPage */
        $resultPage = $this->resultFactory->create(ResultFactory::TYPE_PAGE);

        $this->_eventManager->dispatch(
            'blog_page_render',
            ['post' => $post, 'controller_action' => $this]
        );

        return $resultPage;
    }

In setDesignTheme pass your theme's name and area (frontend|adminhtml) as :

$objectManager->get(\Magento\Framework\View\DesignInterface::class)->setDesignTheme('Theme_Name', 'Area');

Hope this will help others :)

Answer 2

See vendor/magento/framework/App/Area.php

It uses: $this->_getDesign()->setArea($this->_code)->setDesignTheme($theme);

and

            $this->_design->loadChange(
                $this->_scopeResolver->getScope()->getId()
            )->changeDesign(
                $this->_getDesign()
            );

loadChange and changeDesign are defined in vendor/magento/module-theme/Model/Design.php

/**
 * Apply design change from self data into specified design package instance
 *
 * @param \Magento\Framework\View\DesignInterface $packageInto
 * @return $this
 */
public function changeDesign(\Magento\Framework\View\DesignInterface $packageInto)
{
    $design = $this->getDesign();
    if ($design) {
        $packageInto->setDesignTheme($design);
    }
    return $this;
}

I hope this helps.

Answer 3

If you want to set theme for specific website in controller then use below code in your controller file.

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$config = $objectManager->get("\Magento\Theme\Model\Config"); 
$storeManager  = $objectManager->get('\Magento\Store\Model\StoreManagerInterface');

//I have used default luma theme ID, You can change it based on theme.
$themeId = 2; 
$theme = $objectManager->get("\Magento\Theme\Model\ThemeFactory")->create()->load($themeId);

$websiteId = $storeManager->getWebsite()->getId();
if ($theme->getId()) {
    $config->assignToStore($theme,[$websiteId],'website');
}

Thanks.