Inheritance and QpaintEvent

[djoul]

You mean I call virtual even my Son and Daughter methods ? I thought it was just for the Mother class !

[fullmetalcoder]

You mean I call virtual even my Son and Daughter methods ? I thought it was just for the Mother class !

At this point thoughtq won't make your code work... Try it and see...

[djoul]

It still doesn t work ...

[fullmetalcoder]

class Mother : public QWidget
{
    Q_OBJECT
 
    public:
        Mother();
        virtual ~Mother();
 
    protected:
        virtual paintEvent(QPaintEvent *e) {}
};
 
class Son : public Mother
{
    Q_OBJECT
 
    public:
        Son();
        virtual ~Son();
 
    protected:
        virtual paintEvent(QPaintEvent *e) { qDebug("Son : paintEvent"); }
}
 
// somewhere in the code :
Son *pSon = ...
pSon->update();

class Mother : public QWidget
{
    Q_OBJECT
 
    public:
        Mother();
        virtual ~Mother();
 
    protected:
        virtual paintEvent(QPaintEvent *e) {}
};
 
class Son : public Mother
{
    Q_OBJECT
 
    public:
        Son();
        virtual ~Son();
 
    protected:
        virtual paintEvent(QPaintEvent *e) { qDebug("Son : paintEvent"); }
}
 
// somewhere in the code :
Son *pSon = ...
pSon->update();

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What does such a code outputs?

[djoul]

In my code, I added the Q_OBJECT that I had forgotten, I tried what you wrote and this is weird, the Son's paintEvent method is never called !!!
I even tried adding a public method draw in my Son class,with just update() in its body.
And then trying son->draw() but nothing happens.
And, if I put just virtual to the Son and Mother paintEvent method I get the error :

V4 error LNK2001: symbole externe non rÚsolu "protected: virtual void __thiscall Mother:aintEvent(class QPaintEvent *)" (?paintEvent@Weather@@MAEXPAVQPaintEvent@@@Z)

I must add =0 to the virtual paintEvent in the Mother class,
or delete the virtual in virtual paintEvent in my Son class.

For me, the natural code would be in the Mother class : virtual void paintEvent(...)=0 and the destructor virtual.
And in My son class : void paintEvent(...){.........} with the destructor not virtual.
(But I almost tried all the possible configurations)

[jacek]

And then trying son->draw() but nothing happens.

What should happen? How did you try to invoke it? How did you create that object?
Could you prepare minimal compilable example that reproduces the problem?

[djoul]

What should happen? How did you try to invoke it? How did you create that object?
Could you prepare minimal compilable example that reproduces the problem?

In my Son paintEvent I create a file and write some stuff in it and I try to draw some text on my widget to be sure the function is called but the file is never created, so my paintEvent method is never called.
In anoter class I just do Son *son = new Son(...);
son->draw() and as I specified draw as public it should work.

I'll try to prepare a minimal example

[gfunk]

Might doublecheck that your Son isVisible() or has updatesEnabled() ?

[djoul]

Might doublecheck that your Son isVisible() or has updatesEnabled() ?

Hehe, some news : updtatesEnabled do nothing but I tried some Son *son = new Son(...).
son->setVisible(true); and then son->update();
And now my paintEvent is called, but I ve new problems : My class Son is supposed to write on a widget but now (I've got a timer that calls update() every second) it creates a new widget each seconds and writes on it.
But that s a different problem, I think it comes from passing the original widget to the Son, I ll dig on it.
Thank you all for your help !

[jacek]

it creates a new widget each seconds and writes on it.
But that s a different problem, I think it comes from passing the original widget to the Son, I ll dig on it.

Why do you create new widgets if Son is a widget too? Wouldn't it be enough to redraw Son?

[djoul]

Why do you create new widgets if Son is a widget too? Wouldn't it be enough to redraw Son?

But I don t want to create new ones ! Qt does ...
The architecture is :
I've got a class Bck1 and Bck2. In both classes I do some drawing with QPaintEvent (the 2 classes are Widgets).
I ve got then the class Mother with his Son.
And I want the Son to do some drawings in bot he Bck1 and Bck2.
My problem is : Son is not a Widget but he must inherit from QWidget to know where he must paint ?

#include <QWidget>
 
class Bck1: public QWidget
{
	Q_OBJECT
 
	public : 
		Bck1(QWidget *parent = 0);	
		~Bck2();
		...	
	protected :
		void paintEvent(QPaintEvent *event);	
		void mousePressEvent(QMouseEvent *event);
		void keyPressEvent(QKeyEvent *event);
...}
 
#include <QWidget>
 
class Bck2: public QWidget
{
	Q_OBJECT
 
	public : 
		Bck2(QWidget *parent = 0);	
		~Bck2();
 
	protected :
		void paintEvent(QPaintEvent *event);	
}
 
 
#include <QWidget>
 
 
class Mother: public QWidget 
{
	Q_OBJECT
 
	public :
		Mother(QWidget *parent=0);
		virtual ~Mother();	
	protected :
		virtual void paintEvent(QPaintEvent *event)=0;
 
 
};
 
#include <QWidget>
 
class Son : public Mother
{
 
	Q_OBJECT
 
	public : 
		Son(.....);//do I need to put Son(QWidget *parent=0) ... ?????
		 ~Son();
 
	protected :
		  void paintEvent(QPaintEvent *event);
}

#include <QWidget>

class Bck1: public QWidget
{
	Q_OBJECT

	public : 
		Bck1(QWidget *parent = 0);	
		~Bck2();
		...	
	protected :
		void paintEvent(QPaintEvent *event);	
		void mousePressEvent(QMouseEvent *event);
		void keyPressEvent(QKeyEvent *event);
...}

#include <QWidget>

class Bck2: public QWidget
{
	Q_OBJECT

	public : 
		Bck2(QWidget *parent = 0);	
		~Bck2();

	protected :
		void paintEvent(QPaintEvent *event);	
}


#include <QWidget>


class Mother: public QWidget 
{
	Q_OBJECT

	public :
		Mother(QWidget *parent=0);
		virtual ~Mother();	
	protected :
		virtual void paintEvent(QPaintEvent *event)=0;
	

};

#include <QWidget>

class Son : public Mother
{

	Q_OBJECT

	public : 
		Son(.....);//do I need to put Son(QWidget *parent=0) ... ?????
		 ~Son();

	protected :
		  void paintEvent(QPaintEvent *event);
}

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Does it seems ok ? I never know if I need to specify *parent or *parent=0, and if I need to put Qwidget *parent in the Son constructor ???

[jacek]

But I don t want to create new ones ! Qt does ...

Qt does only what you tell it to do.

Indeed, the problem is in constructor. If you create a widget without a parent, it will be created as a standalone window. So your constructor should be implemented like this:

Son::Son( QWidget *parent ) 
   : Mother( parent )
{
   ...
}

Son::Son( QWidget *parent ) 
   : Mother( parent )
{
   ...
}

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And the Mother class must pass this parent to QWidget's constructor.

I never know if I need to specify *parent or *parent=0

That "= 0" part only indicates a default value for the parameter.