magento2 Programmatically change theme in runtime

Question

I have a cookie variable mobile-application = "yes". I need to set a custom theme depends on this variable in magento2. I've already created a custom theme. How I can set it programmatically in runtime. In magento1 works this example:

<models>
    <core>
        <rewrite>
            <design>Packagename_Modulename_Model_Design</design>
        </rewrite>
    </core>
</models>

Rewrite PHP code

  public function loadChange($storeId, $date = null)
    {
        $result = $this->getResource()
            ->loadChange($storeId, $date);

        if (!empty($result)) {
            if (!empty($result['design'])) {
                $tmp = explode('/', $result['design']);
                $result['package'] = $tmp[0];
                $result['theme'] = $tmp[1];
            }

            $this->setData($result);
        }
        // your custom code goes here
        // custom condition
        if(true) {
            $result['package'] = 'default';
            $result['theme'] = 'modern';
            $this->setData($result);
        }

        return $this;
    }

Has anybody experience with this point for magetno2?

Answer 1

You can try the below code to update the theme on runtime in Magento 2.

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

However, you can use the dependency injection in your custom module instead of the $objectManager.

EDIT:

app/code/Vendor/Module/etc/events.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="layout_load_before">
        <observer name="layout_load_before_custom" instance="Verndor\ModuleName\Observer\ChangeTheme" />
    </event>
</config>

Hope it will help!!!