Magento – Constructor for Magento Controller

I found Solution. Good trick

<global>
  <events>
<controller_action_predispatch_mycustomcontrollerhandler>
 <observers>
        <controller_action_before>
            <class>Mycustom_Custom_Model_Observer</class>
            <method>myFunction</method>
        </controller_action_before>
    </observers>
 </controller_action_predispatch_mycustomcontrollerhandler>

For example I need to call event On Product listing Page I use

 <controller_action_predispatch_catalog_product_list>

Per Robbie's suggestion I created:

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="controller_action_predispatch">
      <observer name="my_observer" instance="Module\Path\To\MyClass" shared="false" />
  </event>
</config>

Then created observer class

<?php 

namespace Module\Namespace\Path;

use Magento\Framework\Event\ObserverInterface;

class MyClass implements ObserverInterface
{
    public function execute(\Magento\Framework\Event\Observer $observer)
   {
       // insert code here
   }

}

From here I injected the required classes for my function and was able to get everything working. Thanks for pointing me in the right direction.