MVC request生命周期

Request Lifecycle

The following diagram shows how an application handles a request.

1. A user makes a request to the entry script web/index.php.
2. The entry script loads the application configuration and creates an
   application instance to handle the request.
3. The application resolves the requested route with the help of the
   request application component.
4. The application creates a controller instance to handle the request.
5. The controller creates an action instance and performs the filters
   for the action.
6. If any filter fails, the action is cancelled.
7. If all filters pass, the action is executed.
8. The action loads a data model, possibly from a database.
9. The action renders a view, providing it with the data model.
10. The rendered result is returned to the response application
    component.
11. The response component sends the rendered result to the user’s
    browser.