Block override in Magento2 not working

Question

I'm working on a custom module for magento2. Trying to override the product view block so I can fetch data from an API and pass it into the view. Having read

1. https://community.magento.com/t5/Programming-Questions/Overriding-a-block-in-Magento-2/m-p/6831#U6831
2. Magento 2: Override Magento\Catalog\Block\Product\View Block
3. DI & Extending a Block on Magento 2

I'm still unsuccessful... Here's what I have in my module (Moxune/Moxune):

Block/Product/View.php

<?php
namespace Moxune\Moxune\Block\Product;

use Magento\Framework\View\Element\Template;
use Magento\Catalog\Api\ProductRepositoryInterface;
use Magento\Catalog\Model\Product;
class View extends \Magento\Catalog\Block\Product\View
{
    protected function _toHtml()
    {
        $this->setModuleName($this->extractModuleName('Magento\Catalog\Block\Product\View'));
        return parent::_toHtml();
    }
}

etc/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <preference for="Magento\Catalog\Block\Product\View" type="Moxune\Moxune\Block\Product\View" />
</config>

I then run

rm -rf var/cache var/di var/generation var/page_cache && ./bin/magento setup:di:compile

and navigate to a product detail page. I can tell the overridden block isn't getting called though, because I've changed the _toHtml() body to:

protected function _toHtml()
{
   die('wtf');
}

and also introduced syntax errors and the page continues to load fine. However, if I put a die statement in the _toHtml() of

var/generation/Magento/Catalog/Block/Product/View/Interceptor.php

that shows on the product detail page. So it seems the preference I'm configuring is having no effect?

FWIW - It seems the DI process is creating a new Interceptor based on the configured preference:

var/generation/Moxune/Moxune/Block/Product/View/Interceptor.php

What am I missing?

Answer 1

So I got something working... I discovered the DI configuration was mapping Magento\Catalog\Block\Product\View to Magento\Catalog\Block\Product\View\Interceptor which is not the generated interceptor I was expecting (Moxune\Moxune\Block\Product\View\Interceptor).

I'm not sure exactly why, but my Magento installation (v2.0.4) does not have a view/frontend/templates/product/view.phtml file, so my guess is the block I was trying to override isn't being used. I did find several other (seemingly more granular) template files and decided to shoot for a block that might correspond to one of those.

That said, I've

1. Changed my module's di.xml file to

   <?xml version="1.0"?>
   <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
       <preference for="Magento\Catalog\Block\Product\View\Description"
           type="Moxune\Moxune\Block\Product\View\Description" />
   </config>
   

2. Created the corresponding class

   namespace  Moxune\Moxune\Block\Product\View;
   
   use Magento\Framework\View\Element\Template;
   use Magento\Catalog\Api\ProductRepositoryInterface;
   use Magento\Catalog\Model\Product;
   
   class Description extends \Magento\Catalog\Block\Product\View\Description {
       protected function _toHtml() {   
           $this->setModuleName($this->extractModuleName('Magento\Catalog\Block\Product\View\Description'));
           return parent::_toHtml();
       }   
   }
   

3. Recompiled the DI configuration

   rm -rf var/cache var/di var/generation var/page_cache ; ./bin/magento setup:di:compile
   

Now I seem to be getting into the _toHtml method of my overridden class!