Misunderstanding of using filter when using webapi in mvc4

The two angels started to use the webapi in mvc4 to build a shelf. They did not execute filter in any way during the last day or two.

As we all know, there are four time point functions in actionfilterattribute that can be reloaded. Why are these functions not involved?

After studying it over and over again, I finally figured it out from lunch till now.

Using system. Web. http. filters;

Note: When Using webapi, your actionfilterattribute must be in this namespace, not in system. Web. MVC.

Alas, I still don't know why. I want to study it. Let's add this record.