Slot not getting called, Qt::ConnectionType, Thread

[StarShaper]

I have some strange problems with one SIGNAL/SLOT.

There is one class A::B::Class1 that emits two signals, first without argument, second with one argument.

A::B::J param;
emit orange(param); // Not executed
emit blue();

A::B::J param;
emit orange(param); // Not executed
emit blue();

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In A::C::Class2 the signals and slots are connected. Both connections returns true, but only 1 Slot gets executed, that one without any parameter.

void V::run()
{
    object = new Object();
 
    connect(object, SIGNAL(blue()), this, SLOT(blue_exec()));
    connect(object, SIGNAL(orange(A::B::J&)), this, SLOT(orange_exec(A::B::J&)));
 
    //...
 
    exec();
}

void V::run()
{
    object = new Object();

    connect(object, SIGNAL(blue()), this, SLOT(blue_exec()));
    connect(object, SIGNAL(orange(A::B::J&)), this, SLOT(orange_exec(A::B::J&)));

    //...

    exec();
}

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It is definately a problem with the SIGNAL.

I just did a test with Qt::ConnectionType and a test allocating object on stack with Object object and

void V::run()
{
    Object object;
 
    connect(&object, SIGNAL(orange(A::B::J&)), this, SLOT(orange_exec(A::B::J&)));
 
    //...
 
    exec();
}

void V::run()
{
    Object object;

    connect(&object, SIGNAL(orange(A::B::J&)), this, SLOT(orange_exec(A::B::J&)));

    //...

    exec();
}

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It works. Same thing, if I use Qt:irectConnection.

void V::run()
{
    object = new Object();
 
    connect(object, SIGNAL(orange(A::B::J&)), this, SLOT(orange_exec(A::B::J&)), Qt::DirectConnection);
 
    //...
 
    exec();
}

void V::run()
{
    object = new Object();

    connect(object, SIGNAL(orange(A::B::J&)), this, SLOT(orange_exec(A::B::J&)), Qt::DirectConnection);

    //...

    exec();
}

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That doesn't make sense to me. Why the first connection gets executed, while the second does not. Both are using the same "object"?

[ChrisW67]

Look in the output of your program for warnings like:

QObject::connect: Cannot queue arguments of type 'A::B::J&'                                                          
(Make sure 'A::B::J&' is registered using qRegisterMetaType().)

QObject::connect: Cannot queue arguments of type 'A::B::J&'                                                          
(Make sure 'A::B::J&' is registered using qRegisterMetaType().)

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You will not be able to queue a reference though.

[MarekR22]

if it is a const reference then he can to queue it, but he have to provide meta data for that type of reference.
Not const reference requires Blocking Queued Connection.
See:
http://developer.qt.nokia.com/doc/qt...across-threads
http://developer.qt.nokia.com/doc/qt...ctionType-enum
http://developer.qt.nokia.com/doc/qt...gisterMetaType

[StarShaper]

A::B::J& works! It is registered. But the Signal only works, if object is created in the run() method with Object object;

Read the second part of my posting.

And it also works, if I append Qt:irectConnection.

This is really strange!

Must be some kind of threading issue.

@MarekR22: I'm aware of the threading issues with Connection. But it doesn't make sense to me in my example. Both objects are from the same thread.

---

Added after 11 minutes:

A::B::J& works! It is registered. But the Signal only works, if object is created in the run() method with Object object;

Read the second part of my posting.

And it also works, if I append Qt:irectConnection.

This is really strange!

Must be some kind of threading issue.

@MarekR22: I'm aware of the threading issues with Connection. But it doesn't make sense to me in my example. Both objects are from the same thread.

Yes, it works also with qRegisterMetaType();

If is is a const reference and if I do:

qRegisterMetaType<A::B::J>("A::B::J");
connect(object, SIGNAL(orange(const A::B::J&)), this, SLOT(orange_exec(const A::B::J&)));

qRegisterMetaType<A::B::J>("A::B::J");
connect(object, SIGNAL(orange(const A::B::J&)), this, SLOT(orange_exec(const A::B::J&)));

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