Overriding closeEvent without child class

Reply to Overriding closeEvent without child class on Thu, 17 Nov 2016 06:13:23 GMT

ambershark — Thu, 17 Nov 2016 06:13:23 GMT

@qmad Now that I get what you're asking that is indeed weird. The one thing I can think of as well is that it is not defined in Qt itself, so there is no naming conflict when redefining it.

Seems like a dangerous game that author was playing regardless though. I'd like to write some test code and play with that a bit more. It doesn't seem valid. :)

Reply to Overriding closeEvent without child class on Thu, 17 Nov 2016 06:12:47 GMT

qmad — Thu, 17 Nov 2016 06:12:47 GMT

@ambershark
Yes
In my opinion, the only way it can work is Qt left the closeEvent() function undefined inside QDocWidget class.
Or is there any C++ or Qt magic I am not aware of?

Reply to Overriding closeEvent without child class on Thu, 17 Nov 2016 06:10:24 GMT

ambershark — Thu, 17 Nov 2016 06:10:24 GMT

OH! I think I see what you are talking about. The QDockWidget::closeEvent override was in some random cpp file. Not in the Qt files. I thought you were confused on inheritance and virtual functions, but really you're saying someone just randomly redefined a virtual from a class it wasn't part of?

Reply to Overriding closeEvent without child class on Thu, 17 Nov 2016 06:09:46 GMT

qmad — Thu, 17 Nov 2016 06:09:46 GMT

@jsulm

Let us say class A is defined in a library as follows

class A
{
  public:
   virtual int fun();
};

int A::fun()
{
   cout<<"Called from library";
}

And in my main.cpp can I have below code?

main()
{
  A a;
  a.fun();
}

int A::fun()
{
  cout<<"called from Main";
}

Reply to Overriding closeEvent without child class on Thu, 17 Nov 2016 06:04:30 GMT

ambershark — Thu, 17 Nov 2016 06:04:30 GMT

@qmad I don't think you get it. The QDockWidget IS the child class where it is overridden. You can of course derive from QDockWidget and override it again yourself.

Reply to Overriding closeEvent without child class on Thu, 17 Nov 2016 05:27:30 GMT

jsulm — Thu, 17 Nov 2016 05:27:30 GMT

@qmad Where is this code from?

void QDockWidget::closeEvent(QCloseEvent* e)
{
  //handling close event here
}

It is just a plain old C++ method definition, which in this case happens to be an inherited virtual method, hence it is overridden in QDockWidget.

Reply to Overriding closeEvent without child class on Thu, 17 Nov 2016 04:46:49 GMT

qmad — Thu, 17 Nov 2016 04:46:49 GMT

I can understand if there is a child class of QDocWidget and closeEvent is overriding in it. In this case simply there is a QDockWidget::closeEvent(QCloseEvent* e){----} code. I was assuming that this definition will be already there in Qt libraries. Do you mean, in QtDocWidget, it is only a declaration and they left definition of us ?

Reply to Overriding closeEvent without child class on Wed, 16 Nov 2016 22:24:32 GMT

ambershark — Wed, 16 Nov 2016 22:24:32 GMT

QDockWidget's parent is QWidget. So it is a child to QWidget. And QWidget::closeEvent() is a protected virtual so it can be overridden.

Likewise if you wanted to override closeEvent in a class you derive from QDockWidget you would be able to do that as well.

So the override is legit since QDockWidget is a child of QWidget. ;)

Edit: I really should have read @raven-worx 's answer before I wrote that since he said exactly what I said.

Reply to Overriding closeEvent without child class on Wed, 16 Nov 2016 14:55:13 GMT

raven-worx — Wed, 16 Nov 2016 14:55:13 GMT

@qmad said in Overriding closeEvent without child class:

But there is no child class in this this case.

i am not quite sure what your question is, but i try it anyway.
The QWidget base class implements closeEvent(). Additionally it's declared as virtual