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?