Magento 2: Extend from rewritten block

Question

Originally: There are 2 blocks like this:

namespace Vendor\Module_1\Block;
class ParentBlock{}
class ChildBlock extends ParentBlock {}

Now, I need to rewrite ParentBlock using di.xml:

<preference for="Vendor\Module_1\Block\ParentBlock" type="Vendor\Module_2\Block\ParentBlock" />

namespace Vendor\Module_2\Block;
class ParentBlock extends \Vendor\Module_1\Block\ParentBlock {}

How can I make \Vendor\Module_1\Block\ChildBlock extend from \Vendor\Module_2\Block\ParentBlock?

If there is any more information needed, please tell me.

Thanks in advanced.

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Updated following answers from @Raphael at Digital Pianism.

Thanks for your explanation. And I thought as you said too, but in my case, it doesn't work.

I have to create a new preference for Module_1\ChildBlock. Then I have to create new Module_2\ChildBlock like this:

namespace Vendor\Module_2\Block;
class ChildBlock extends \Vendor\Module_2\Block\ParentBlock {}

Finally, I have to copy all methods from Module_1\ChildBlock to this one.

This is so crazy!!! I don't know what's wrong, as well as how to fix this problem.

Answer 1

The preference will do everything you need for you.

A simplified definition of defining preferences for some classes could be that the new classes will be used instead of the old ones.

So in your case, as you defined a preference for the ParentBlock class, the ChildBlock will automatically extend the new ParentBlock class thanks to your preference

To summarize, everytime Magento 2 is supposed to instantiate Module_1\ParentBlock it will actually instantiate Module_2\ParentBlock instead