[Qt-interest] inheritance problem

[franki]

Friday 26 of February 2010 13:22:12 Eirik Ulvik napisał(a):
> Why don't you create separate QWidget based classes that can be inserted
> into the respective tabs of the QTabWidget? You can use signals/slots
> for communcation between the different parts of the UI.

Hmm, yes didn't thought about it earlier, I could do that, but this was my 
first qt app, and large portion of application is already done, I would have 
to redo all interface, and quite a lot of code.
So this approach I will use next time,
but is it really so difficult to derive new class from my base class 
custPanel_TabWidget ?
When I'm reading howto's about class inheritance it looks simple, so why I get 
this error: invalid use of incomplete type 'struct custPanel_TabWidget'

Do I mess something with header files, or there is something specific in Qt?

greetings
Marek


>
> Eirik
>
> Den 26.02.2010 12:49, skrev franki:
> > 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
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> >>
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