[Qt-interest] inheritance problem

[franki]

Friday 26 of February 2010 21:42:14 Malyushytsky, Alex napisał(a):
> >>But when I'm trying to create class that subclass from
> >> custPanel_TabWidget I get this error: invalid use of incomplete type
> >> 'struct custPanel_TabWidget'
> >>
> >>and the header is like this:
> >>
> >>#include "custpanel.h"
> >>class custPanel_TabWidget;
> >>
> >>class classForTab1: public custPanel_TabWidget {
> >>public:

Hi,

Sorry that I was out for so long, it was a heavy weekend 

>
> First. Let's forget for a second for your goals.
> You can't derive from incomplete type and that is what compiler tells you.
> You can use forward declaration only until compiler does not need to know
> anything about object. It means "class custPanel_TabWidget;" has to be
> replaced with proper #include "custPanel_TabWidget.h"

so the hint is that I have different file name than the class name. My 
custPanel_TabWidget class is defined in custpanel.h - so thats the problem.

>
> Second.
> You can promote each tab widget to whatever class you need.
> That what you normally do, cause each page in the QTabWidget is a widget
> you can subclass QWidget and place specific for the page code in separated
> class.
>
> If you already use designer I would highly recommend to consider promotion
> feature. Otherwise you will have to deal with a fact that instance of the
> widget of the base class you want to derive from is already created and
> this widget is already placed in the layout.

So I've tried this approach, and it gave me a headache.
I'm using Qt Designer 4.4.3 on Debian Lenny.
I can't promote each tab from QTabWidget because designer does not give me 
such an option when I right-click on empty tab, but I can drag-drop QWidget 
from designer menu, put it inside each tab, and promote this widget to custom 
class e.g. custStatus
So the custstatus.h is:

#ifndef CUSTSTATUS_H
#define CUSTSTATUS_H
#include <QObject>
#include <QWidget>

class custStatus: public QWidget
{
        Q_OBJECT
public:
        custStatus(QWidget *parent);
        ~custStatus();
        QWidget *p;
public slots:
        void slot1();
};

#endif

and custstatus.cpp:

#include <QObject>
#include <QtGui>
#include "custstatus.h"

custStatus::custStatus(QWidget *parent) : QWidget(parent) {
        p=parent;
        qDebug() << "custStatus started";
}
void custStatus::slot1() {
        qDebug() << "custStatus::slot1 started";
//        this->p5_lineEdit->setText("Test msg");
}

Now, as I understand custStatus class derived from QWidget is a placeholder 
for all widgets created inside it.
But, how do I access those widgets? Lets say I have QLineEdit called 
p5_lineEdit, I was unable to access it by pointer "this" or by saved "parent"

Signal created in Qt Designer invoked my custom slot "slot1()" but 
this->p5_lineEdit->setText("Test msg"); 
gives an error:
'class custStatus' has no member named 'p5_lineEdit'

Also in that class custStatus I need access to other objects which are holding 
connection to db, current customer ID, etc.
I could imagine some function like custStatus::Initialize which would be 
called from custPanel_TabWidget (my base class) and variables like db 
connection and other would be passed to this new class.
Somethig like:
Ui::custPanel_TabWidget->widget->Initialize(ItSql *itsql,QVariant cust_id)

But is this the way it should be done?
Or I get it completely wrong?

Greetings
Marek

>
>
> Alex
>
>
>
> -----Original Message-----
> From: qt-interest-bounces at trolltech.com
> [mailto:qt-interest-bounces at trolltech.com] On Behalf Of franki Sent:
> Friday, February 26, 2010 3:49 AM
> To: qt-interest at trolltech.com
> Subject: Re: [Qt-interest] inheritance problem
>
> Thursday 25 of February 2010 23:57:00 Malyushytsky, Alex napisał(a):
> > You derive from the class you need to derive from.
> >
> > If I understood your problem (which I am not sure) you want  to use your
> > derived class instead of QTabWidget. In this case you might use
> > "Promoting Widgets" technique.
> > http://doc.trolltech.com/4.6/designer-using-custom-widgets.html
>
> Hi,
>
> I've read about promoting widgets and I think it's not what I need.
> Maybe I explain it in different words:
> The way I'm doing my application now is called: "The Single Inheritance
> Approach", so in my case QTabWidget is placeholder for all widgets that
> constitute the user interface.
> Next, I sublassed this QTabWidget with my class custPanel_TabWidget
> and the header file is like this:
>
> #include "ui_custpanel.h"
> class custPanel_TabWidget: public QTabWidget
> {
>         Q_OBJECT
> public:
>         custPanel_TabWidget ();
>         ~custPanel_TabWidget();
>         Ui::custPanel_TabWidget cp;
> }
>
> so now all widgets created inside QTabWidget (by Qt Designer) are
> accessible by this variable "cp", and when I need to connect some signals,
> genrated for example by pushButtons, with functions inside
> custPanel_TabWidget then it is simple as that:
> connect(cp.saveButton,SIGNAL(clicked()),this,SLOT(saveValues()))
>
> But the problem is, that I have lets say 10 tabs in QTabWidget (each tab
> present some different data for user, and each use different functions to
> manage this data) and all these functions are inside class
> custPanel_TabWidget - so this file has grown big, and does not look clean.
>
> So I thought about creating class for each tab, and that class should
> maintain functions needed to interact with user.
> Now is what I'm not sure:
> As I understand this now, if I subclass from class custPanel_TabWidget I
> will be able to access "cp" variable (which means easy access to all
> widgets in QTabWidget just like this->cp), and I will be able to access all
> public functions created inside custPanel_TabWidget, so the inheritance
> model would look like this
> QTabWidget -> custPanel_TabWidget ->classForTab1
>
> But when I'm trying to create class that subclass from custPanel_TabWidget
> I get this error:
> invalid use of incomplete type 'struct custPanel_TabWidget'
>
> and the header is like this:
>
> #include "custpanel.h"
> class custPanel_TabWidget;
>
> class classForTab1: public custPanel_TabWidget
> {
> public:
>         classForTab1 ();
>         ~classForTab1();
> };
>
> So are there some mistakes in what I think I know about inheriting from
> other classes, and how to make this class "classForTab1"
>
> The second apporoach that I mentioned in previous post, was to create new
> class and pass it variables like "cp" (to access widgets inside QTabWidget)
> and others - to access objects holding connection to sql, and finally
> pointer to the base class (custPanel_TabWidget)
> So the constructor for classForTab1 looks like this:
> classForTab1::classForTab1(Ui::custPanel_TabWidget cp,ItSql *itsql,QVariant
> cust_id,custPanel_TabWidget *parent) : QWidget ()
>
> It works fine, but it does not look clean.
> So please help.
>
> Greetings
> Marek
>
> > In your case:
> >
> > - You subclass from the QTabWidget
> > - in designer place QTabWidget and then promote it.
> >
> > Hope this helps,
> >    Alex
> >
> >
> >
> > -----Original Message-----
> > From: qt-interest-bounces at trolltech.com
> > [mailto:qt-interest-bounces at trolltech.com] On Behalf Of franki Sent:
> > Thursday, February 25, 2010 8:11 AM
> > To: qt-interest at trolltech.com
> > Subject: [Qt-interest] inheritance problem
> >
> > Hi,
> >
> > I've application with QMainWindow and tabWidget as a centralWidget,
> > class that maintains this tabWidget is called custPanel_TabWidget
> > some piece of custpanel.h:
> >
> > #ifndef CUSTPANEL_H
> > #define CUSTPANEL_H
> > #include "ui_custpanel.h"
> >
> > class custPanel_TabWidget: public QTabWidget
> > {
> >         Q_OBJECT
> > public:
> >         custPanel_TabWidget (QWidget *parent,QVariant cust_id,ItSql
> > *itsql); ~custPanel_TabWidget();
> >         Ui::custPanel_TabWidget cp;
> > }
> >
> > I wanted each tab to be maintained by its own class, because there is so
> > many functions that custPanel_TabWidget started to be huge mess.
> > so I did class e.g. Notify
> > header notify.h:
> >
> > #ifndef NOTIFY_H
> > #define NOTIFY_H
> > #include <QObject>
> > #include "custpanel.h"
> >
> > class custPanel_TabWidget;
> >
> > class Notify: public custPanel_TabWidget
> > {
> > public:
> >         Notify ();
> >         ~Notify();
> > };
> >
> > but during compilation, I get error:
> > invalid use of incomplete type 'struct custPanel_TabWidget'
> >
> > I've googled somewhere that I should derive from Ui::custPanel_TabWidget
> > instead of custPanel_TabWidget, because this class is called that way in
> > ui_custpanel.h - which is true.
> > But, when I've tried to derive from Ui::custPanel_TabWidget, program
> > compile fine, but I can't access any widget on tabWidget, and in fact
> > which class do I derive from?
> >
> > Second sollution for me, that I've proven to work earlier, was to pass
> > some variables to new class instead of deriving from custPanel_TabWindow,
> > and maintain all function related to this tab in that new class.
> > So in that case, the constructor is like this:
> >
> > Abonament::Abonament(Ui::custPanel_TabWidget cp,ItSql *itsql,QVariant
> > cust_id,custPanel_TabWidget *parent) : QWidget ()
> >
> > And this second approach works fine for me, but which one is better, or
> > which one is recommended?
> >
> > Thanks in advance
> > Marek
> > _______________________________________________
> > Qt-interest mailing list
> > Qt-interest at trolltech.com
> > http://lists.trolltech.com/mailman/listinfo/qt-interest
> >
> >
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