Overriding Block file is not working in Magento 2

Question

Today I am trying to overwrite the \Magento\Sales\Block\Adminhtml\Order\View file, but it's not working. The same coding working on core files.

My Code is

<?php
namespace SR\StackExchange\Block\Adminhtml\Order;
class View extends \Magento\Sales\Block\Adminhtml\Order\View
{
 /**
 * Get URL for back (reset) button
 *
 * @return string
 */
 public function getCustomOrderUrl()
 {
 $params = [
 'id' => $this->getOrderId(),
 'store' => 0
 ];
 return $this->getUrl('stackexchange/stackexchange/order');
 }
 /**
 * Constructor
 *
 * @return void
 * @SuppressWarnings(PHPMD.CyclomaticComplexity)
 * @SuppressWarnings(PHPMD.NPathComplexity)
 * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
 */
 protected function _construct()
 {
 $this->buttonList->add(
 'custom_button',
 [
 'label' => __('Custom Button'),
 'class' => 'action-secondary',
 'on_click' => sprintf("location.href = '%s';", $this->getCustomOrderUrl()),
 ]
 );
 parent::_construct();
 }
}

etc/adminhtml/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd"> 
 <type name="Magento\Sales\Block\Adminhtml\Order\View">
 <plugin name="custom_button" type="SR\StackExchange\Block\Adminhtml\Order\View" sortOrder="1"/>
 </type>
</config>

Answer 1

I think you misunderstanding plugins and preferences.

If you want to override an entire class you need to use preferences:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd"> 
 <preference for="Magento\Sales\Block\Adminhtml\Order\View"
 type="SR\StackExchange\Block\Adminhtml\Order\View" />
</config>

You can get a good read about the differences between plugins and preferences here: Magento2: what is the basic difference between plugin and preference?