[Qt-interest] how to pass the reference to QMap to other class

[franki]

Friday 09 September 2011 14:21:58 BERAUD Alexandre napisał(a):
> QMap<int,DataStruct>& myMap;
> This is an uninitialized reference, which is invalid and is just
> tolerated by your compiler.
>
> myMap(firstClass->getMap())
> Here you use the copy constructor of the class and I guess some hidden
> dereference is involved.
> In my opinion it is better to access the QMap through the firstClass
> pointer because the use of references often leads to unreadable code
> with the compiler performing some magic behind the scene.

thanks for answer, there must be some connection between my variable myMap in 
SecondClass and original QMap in first, because if I modify obcject in first 
class I can read it in second, only when I add additional object in first, I 
can't see it in second one.
but just out of curiosity, is there a way to pass reference to QMap to other 
class?
I'm using 4.7.4 Qt and Linux platform

best regards
Marek

>
> Regards,
>
> Alex
>
> Le 09/09/2011 12:38, franki a écrit :
> > Hi all,
> >
> > I have one class where i have QMap which has some data, I want to be
> > able to easly access this data in second class, so what I want is to
> > pass this QMap from first class to second class as a reference
> > (without copying data).
> >
> > I googled and I've done it like this (snippet of code):
> >
> > first class header :
> >
> > public:
> >
> > FirstClass(QObject *parent)
> >
> > QMap<int,DataStruct> myMap;
> >
> > public slot:
> >
> > QMap<int,DataStruct>& getMap();
> >
> > first class body:
> >
> > QMap<int,DataStruct>& FirstClass::getMap() {
> >
> > return myMap;
> >
> > }
> >
> > second class header:
> >
> > public:
> >
> > SecondClass(Ui::MainPages m,FirstClass *firstClass);
> >
> > private:
> >
> > Ui::MainPages mp;
> >
> > FirstClass *firstClass;
> >
> > QMap<int,DataStruct>& myMap;
> >
> > second class body:
> >
> > SecondClass::SecondClass(Ui::MainPages m,FirstClas *firstClass):
> > QWidget(),myMap(firstClass->getMap())
> >
> > {
> >
> > mp=m;
> >
> > this->firstClass=firstClass;
> >
> > }
> >
> > So the problem is wierd, when I change data of the item in QMap in
> > firstClass I can see the change in secondClass by accessing private
> > variable myMap,
> >
> > but when I add new member to QMap in firstClass I can't see this new
> > member in secondClass by using private variable myMap, although I can
> > access this new member when I'm using pointer to first class like this:
> >
> > firstClass->myMap
> >
> > What is wrong with this, and how should I do that properly?
> >
> > I'm aware that in second class I can access QMap by pointer to first
> > class:
> >
> > firstClass->myMap
> >
> > but I wanted to have reference to myMap in second class without using
> > pointer to first class.
> >
> > please advise me.
> >
> > best regards
> >
> > Marek
> >
> >
> >
> > _______________________________________________
> > Qt-interest mailing list
> > Qt-interest at qt.nokia.com
> > http://lists.qt.nokia.com/mailman/listinfo/qt-interest