Qt-interest Archive, April 2007
Pointers in QVariant?
Message 1 in thread
Hi,
I am missing the possibility to acces void* pointers by QVariant... it is not
the example for good code to use something like that, but it helps a lot :-)
(Maybe on step better could be Pointers to QObjects, don't know...)
If you build a attr/value-Pair QMap<QString,QVariant>, collect a lot of them
in a list, you have something like
[MyList]
1: name=first, id=1, ...
2: name=2nd, id=2
...
what I'd like to have is
1: ..., childs=0x3E87456
-> [MyChilds]
1: name=child one, id=1...
if these lists (and sublists/trees) are loaded from and saved to xml nodes, I
could do fantastic things without knowing whats inside...
Is there any hint or do I just have to add my own QVariant type "Ptr"?
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Message 2 in thread
"J. Preiss" <auba@xxxxxxx> wrote in message
news:200704292250.01672.auba@xxxxxxxxxx
> Hi,
> I am missing the possibility to acces void* pointers by QVariant... it
> is not
> the example for good code to use something like that, but it helps a lot
> :-)
> (Maybe on step better could be Pointers to QObjects, don't know...)
>
> If you build a attr/value-Pair QMap<QString,QVariant>, collect a lot of
> them
> in a list, you have something like
> [MyList]
> 1: name=first, id=1, ...
> 2: name=2nd, id=2
> ...
>
> what I'd like to have is
> 1: ..., childs=0x3E87456
> -> [MyChilds]
> 1: name=child one, id=1...
>
> if these lists (and sublists/trees) are loaded from and saved to xml
> nodes, I
> could do fantastic things without knowing whats inside...
>
> Is there any hint or do I just have to add my own QVariant type "Ptr"?
You can use the meta type system to add types to QVariant, and that
includes pointer-types. But if your data is serialized from XML, then it
might be worth considering if the data is not best stored in value-types.
If you want to get a pointer to the object stored in the QVariant, then
use QVariant::data and QVariant::constData (undocumented, but public
functions).
Volker
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Message 3 in thread
> You can use the meta type system to add types to QVariant, and that
> includes pointer-types. But if your data is serialized from XML, then it
> might be worth considering if the data is not best stored in value-types.
Oh, of course they are - if the access type is via files. Then I have a
QHash<int,QVariant> at the end. But if one attribute is a pointer type, I
want to get again a pointer to a QHash<int,QVariant>. After all, I get a tree
structure.
> If you want to get a pointer to the object stored in the QVariant, then
> use QVariant::data and QVariant::constData (undocumented, but public
> functions).
So I only have to do a
typedef QHash<int,QVariant> MyList;
qRegisterMetaType<MyList*>("Listptr");
or even only a
Q_DECLARE_METATYPE(MyList)
and thats all? Then I can do a
void doIt(MyList* list)
{
QVariant var = list;
}
void orNot(QVariant& var)
{
MyList* list = var;
}
? Would be really magic if so...
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