QObject->inherits() troubles: Keeps returning false

[JPNaude]

Hi

I use the QObject->inherits() function in a couple of places, in the one place it works but in the other place it does not and I can't figure out why.

First usage case = works
I return a list of objects which implements a specific interface. In obj the interface is declared using Q_INTERFACES, but according to the documentation inherits is not meant only for interfaces.

QString iface_type = "IConfigPage";
if (obj->inherits(meta_type.toAscii().data()))
   // do some stuff

QString iface_type = "IConfigPage";
if (obj->inherits(meta_type.toAscii().data()))
   // do some stuff

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Second usage case = does not work
I filter subjects in order to allow only certain types of objects to continue past the if statement. Variable is the name of a base class in my project.

QString meta_type = "Variable";
if (obj->inherits(meta_type.toAscii().data()))
   // do some stuff

QString meta_type = "Variable";
if (obj->inherits(meta_type.toAscii().data()))
   // do some stuff

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Since these two are almost exactly the same, I suspect that it is related to class Variable. A simplified version of this class is shown below:

class QTSF_SHARED_EXPORT Variable : public QObject
{
Q_OBJECT
 
public:
     explicit Variable(const QString& variableType, QObject *parent = 0);
     Variable(const Variable &other);
     virtual ~Variable() {};
}

class QTSF_SHARED_EXPORT Variable : public QObject
{
Q_OBJECT

public:
     explicit Variable(const QString& variableType, QObject *parent = 0);
     Variable(const Variable &other);
     virtual ~Variable() {};
}

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and below is a variable type based on the Variable base class:

class QTSF_SHARED_EXPORT Matrix : public Variable
 {
Q_OBJECT
 
friend class MatrixPrivate;
public:
       Matrix(QObject *parent = 0);
 
...
...

class QTSF_SHARED_EXPORT Matrix : public Variable
 {
Q_OBJECT

friend class MatrixPrivate;
public:
       Matrix(QObject *parent = 0);

...
...

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Any ideas on why it is not working would be much appreciated.
Thanks
Jaco

[aamer4yu]

QString meta_type = "Variable";
if (obj->inherits(meta_type.toAscii().data()))
// do some stuff

Whats obj in this ?

[Lykurg]

I don't know what magic you do with QTSF_SHARED_EXPORT, but try if your code would work with:

if (qobject_cast<Variable *>(obj))

if (qobject_cast<Variable *>(obj))

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[caduel]

check if moc is run for those classes
(the 3 ingredients for the qt magic to work are: derive from QObject, do not forget Q_OBJECT macro, *and* run moc - e.g. by putting the header file inside the .pro file's HEADERS section)

[JPNaude]

Whats obj in this ?

That if statement lies within a function which takes a QObject pointer as an argument: function(QObject* obj)

[JPNaude]

I don't know what magic you do with QTSF_SHARED_EXPORT, but try if your code would work with:

if (qobject_cast<Variable *>(obj))

if (qobject_cast<Variable *>(obj))

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Hmmm, the code lies in a library, and QTSF_SHARED_EXPORT is defined as follows:

#if defined(QTSF_LIBRARY)
# define QTSF_SHARED_EXPORT Q_DECL_EXPORT
#else
# define QTSF_SHARED_EXPORT Q_DECL_IMPORT
#endif

So it should not make a different I believe

[JPNaude]

check if moc is run for those classes
(the 3 ingredients for the qt magic to work are: derive from QObject, do not forget Q_OBJECT macro, *and* run moc - e.g. by putting the header file inside the .pro file's HEADERS section)

Thanks. I double checked and moc_* files are created for both Variable and Matrix classes. So it does not seem like this is the problem.