Why virtual bool OnInit()? Why virtual? Topic is solved

[riruilo]

Hi friends!

Just a easy question (for you). Why do you declare OnInit as virtual?

I started with wxWidgets reading this
http://www.wxwidgets.org/docs/tutorials/hello.htm
and I don't understand why oninit is virtual.

Thanks a lot.

[JimFairway]

Hi,

It's virtual because if you derive your own class from wxApp, you can override the default OnInit method with one of your own if you choose.


See http://www.cplusplus.com/doc/tutorial/polymorphism.html

Jim

[riruilo]

Hi,

It's virtual because if you derive your own class from wxApp, you can override the default OnInit method with one of your own if you choose.


See http://www.cplusplus.com/doc/tutorial/polymorphism.html

Jim

Thanks for reply.

Why should i derieve from MyApp? Why not direcly from wxApp?

Thanks.

[jacmoe]

Why should i derieve from MyApp? Why not direcly from wxApp?

What he said.

[vdell]

Why should i derieve from MyApp? Why not direcly from wxApp?

"MyApp" refers to the class that derives from wxApp:

Code: Select all

class MyApp : public wxApp
{
...
};

Naturally the class can be called whatever you want.

HTH

[TrV]

It's virtual because if you derive your own class from wxApp, you can override the default OnInit method with one of your own if you choose.

Why should i derieve from MyApp? Why not direcly from wxApp?

JimFairway is right, but riruilo asks a good question : OnInit() is declared virtual in class wxApp to ensure that MyApp use the "last" form of OnInit().
But there's no reel need to declare OnInit() virtual into MyApp. It's only usefull if MyApp is also derived.

Answer is: as nobody knows what can be future uses of this class, declaring OnInit() allows it to be overriden. But if you're 100% sure you'll never derive from MyApp, you can declare OnInit() as non-virtual.

[Frank]

A function that is declared as virtual is always virtual. In every derived class. whether you explicitly write "virtual" in your derived class or not.

So if you need a "virtual" to remind you, that this function is virtual use it. If not, don't. Makes no difference.

[TrV]

A function that is declared as virtual is always virtual. In every derived class. whether you explicitly write "virtual" in your derived class or not.

So if you need a "virtual" to remind you, that this function is virtual use it. If not, don't. Makes no difference.

I made the test. It's right. I didn't know that. So, virtual or no virtual, that's same thing for users of wxApp class.

[riruilo]

A function that is declared as virtual is always virtual. In every derived class. whether you explicitly write "virtual" in your derived class or not.

So if you need a "virtual" to remind you, that this function is virtual use it. If not, don't. Makes no difference.

So, do you say OnInit in wxApp is virtual, but people usually write virtual on their derived class to remember it is a virtual func? Am I right?

[jfouche]

Exactly

[riruilo]

Thanks a lot. Now it is clear.

[jacmoe]

jfouche's answer is correct, but I find it weird that you accept his answer, and not the others who helped you out..

[riruilo]

jfouche's answer is correct, but I find it weird that you accept his answer, and not the others who helped you out..

Excuse me. I don't know how to accept all of them.
All your replies are very helpful for me.

[jacmoe]

Excuse me. I don't know how to accept all of them.
All your replies are very helpful for me.

When you view your topic, you have the option to choose Assist/Accept (the buttons are where your edit/delete/quote buttons are).
Pick assisting answers first, then choose the best answer as the accepted answer.