How to exactly know what event will be triggered when and what data can be captured in observer?

Question

I am quite unsure of how to know which event will occur when. I cannot understand what arguments I should capture in observer unless I find exactly what I want in internet.

Answer 1

In Magento 2, some observers will be dispatched in core code like this:

$this->_eventManager->dispatch('catalog_product_collection_load_after', ['collection' => $this]);

As you see, you can get argument by call $observer->getEvent()->getColelction();

Also, some observers will not. In this situation, you have to use some IDE support debug to get what the event dispatch!.