Why do *Event functions declared in QWidget as protected ?

[burkav84]

Why do *Event functions declared in QWidget as protected ? What's the reason ?

[Gopala Krishna]

Why do *Event functions declared in QWidget as protected ? What's the reason ?

*Event functions are mainly provided to override default response of a widget for an event and hence for a user its only useful when he overrides the class. This means only QWidget and classes derived from it are the accessors of *Event members and hence they are protected.
That too making them public would mean a possible misuse of these functions by user - say for example when a user "calls" QWidget::mouseMoveEvent() instead of QCoreApplication::sendEvent() which is what the user would have probably wanted to do.

[jpn]

Why do *Event functions declared in QWidget as protected ? What's the reason ?
Because they are called "by the framework" (*). One is not not supposed to call them outside by hand (this is why they are not public). One can re-implement a virtual event handler in a subclass (this is why they are not private).

(*) Notably QWidget::event() does the job of identifying different kind of events and delivering them into specialized event handlers if appropriate, like QWidget::mousePressEvent(), QWidget::keyPressEvent() and so on..

[burkav84]

One can re-implement a virtual event handler in a subclass (this is why they are not private).

But if it declared as private, it is possible to reimplement it in subclass :confused:
Why not to implement them as private ? It may be caused that in reimplemented event handler it may be need to call QWidget::*Event() of the base class. Correct ?

[jacek]

But if it declared as private, it is possible to reimplement it in subclass
If they were private, they wouldn't be accessible in subclasses.

[burkav84]

One can re-implement a virtual event handler in a subclass (this is why they are not private).

But if it declared as private, it is possible to reimplement it in subclass :confused:
Why not to implement them as private ? It may be caused that in reimplemented event handler it may be need to call QWidget::*Event() of the base class. Correct ?

[Gopala Krishna]

But if it declared as private, it is possible to reimplement it in subclass :confused:
Why not to implement them as private ? It may be caused that in reimplemented event handler it may be need to call QWidget::*Event() of the base class. Correct ?

You can implement but you can't call base method in sub classes.

[Gopala Krishna]

Check this link http://www.parashift.com/c++-faq-lite/basics-of-inheritance.html#faq-19.5

[jpn]

As already mentioned, you cannot access anything private (unless declared as a friend).

What's the difference between public, private, and protected? (http://www.parashift.com/c++-faq-lite/basics-of-inheritance.html#faq-19.5)

Edit: Gopala Krishna, did you modify the post of yours? It looks different than by the time I started replying.. :p

[burkav84]

Thank's Gopala Krishna and jpn for answers and links.

[Gopala Krishna]

Edit: Gopala Krishna, did you modify the post of yours? It looks different than by the time I started replying.. :p

No I posted 2 replies one after other. You should have started to reply after the 1st reply . Just a sheer coincidence !! ;)