qt call ocx

xiaolin

1、environment：windows10 64bit; qt 5.15.2 ; msvc2019 64bit；qt creator 5.0.3

2、QAxObject::generateDocumentation() ，The api exported by the method is as follows：

slot:
int GetStagePosition(QVariant& x, QVariant& y, QVariant& z, QVariant& t, QVariant& r, QVariant& m);

The documentation gives examples of calls：

int GetStagePosition (QVariant& x, QVariant& y, QVariant& z, QVariant& t, QVariant& r, QVariant& m) [slot]

Connect a signal to this slot:

 QObject::connect(sender, SIGNAL(someSignal(QVariant&, QVariant&, QVariant&, QVariant&, QVariant&, QVariant&)), object, SLOT(GetStagePosition(QVariant&, QVariant&, QVariant&, QVariant&, QVariant&, QVariant&)));

Or call the function directly:

 QVariantList params = ...
 int result = object->dynamicCall("GetStagePosition(QVariant&, QVariant&, QVariant&, QVariant&, QVariant&, QVariant&)", params).toInt();

3、First attempt：

QObject::connect(this,  SIGNAL( sig_GetStagePosition(QVariant&,QVariant&,QVariant&,QVariant&,QVariant&,QVariant&) ), m_axObject, SLOT( GetStagePosition(QVariant&,QVariant&,QVariant&,QVariant&,QVariant&,QVariant&) ));

sig_GetStagePosition：This is my custom signal.
m_axObject:This is the QAxObject object.

I trigger the signal inside the button，

QVariant varX, varY, varZ, varT, varR, varM;
emit sig_GetStagePosition(varX, varY, varZ, varT, varR, varM);

The console outputs an error when I click the button to trigger the signal：

QAxBase: Error calling IDispatch member GetStagePosition: Type mismatch in parameter 0

4、When I tried the second method：

QVariant qvarX, qvarY, qvarZ, qvarT, qvarR, qvarM;

QVariantList args;
args << qvarX << qvarY << qvarZ << qvarT << qvarR << qvarM;

m_axObject->dynamicCall("GetStagePosition(QVariant&, QVariant&, QVariant&, QVariant&, QVariant&, QVariant&)", args);

When I click the button to run it, it still reports the same error：

QAxBase: Error calling IDispatch member GetStagePosition: Type mismatch in parameter 0

I don't know what the problem is, thank you very much for answering my question

JonB

@xiaolin
I think the following is an outline of the answer.

Your method requires QVariant & parameters, i.e. non-const references to QVariants, because these are not "in" parameters, they are "out" parameters which GetStagePosition is going to fill. Right?

But QVariant QAxBase::dynamicCall(...) accepts only const QVariant & parameters, i.e. "in"-only parameters. And it says

All parameters are passed as strings; it depends on the control whether they are interpreted correctly, and is slower than using the prototype with correctly typed parameters

Hence the "type mismatch" error, and this is never going to work.

I think that QAxBase::dynamicCall() can only be called with in-string parameters. To do what you want --- pass in "out"-QVariant & parameters --- I guess you have to use queryInterface() and call the function directly with the desired parameters, as shown in the last example at that link.

Having said that, I see there is a different overload: QVariant QAxBase::dynamicCall(const char *function, QList<QVariant> &vars), and that says:

The QVariant objects in vars are updated when the method has out-parameters.

So that ought work. For that I suspect/wonder whether your call should not specify the parameters? So maybe:

m_axObject->dynamicCall("GetStagePosition", args);
// or
m_axObject->dynamicCall("GetStagePosition()", args);
// or
m_axObject->dynamicCall("GetStagePosition(QList<QVariant> &)", args);

? I am unable to find any example on the web which uses this overload, so you may have to play!

You might want to also read https://www.codeproject.com/Tips/751240/Using-COM-Binary-Interface-with-Cplusplus and and/or https://www.qtcentre.org/threads/49796-dynamicCall-with-in-out-SAFEARRAY(VARIANT_BOOL)*-parameter

xiaolin

@JonB Thank you very much for your patient answer，Thanks.
I understand that adding a const argument cannot be used as an out parameters，So I also tried dynamicCall() second overload.

Based on the attempt you gave me, I also ran the test again.

First:

QVariant qvarX, qvarY, qvarZ, qvarT, qvarR, qvarM;

QList<QVariant> args;
args << qvarX << qvarY << qvarZ << qvarT << qvarR << qvarM;

m_axObject->dynamicCall("GetStagePosition", args);

the same error:

QAxBase: Error calling IDispatch member GetStagePosition: Type mismatch in parameter 0

Second:

QVariant qvarX, qvarY, qvarZ, qvarT, qvarR, qvarM;

QList<QVariant> args;
args << qvarX << qvarY << qvarZ << qvarT << qvarR << qvarM;

m_axObject->dynamicCall("GetStagePosition()", args);

Error occurs change：

QAxBase: Error calling IDispatch member GetStagePosition: Non-optional parameter missing

Third：

QVariant qvarX, qvarY, qvarZ, qvarT, qvarR, qvarM;

QList<QVariant> args;
args << qvarX << qvarY << qvarZ << qvarT << qvarR << qvarM;

m_axObject->dynamicCall("GetStagePosition(QList<QVariant> &)", args);

It's the same mistake：

QAxBase: Error calling IDispatch member GetStagePosition: Type mismatch in parameter 0

I read the link you gave at the end，I didn't understand a few parts of the article.

inline int GetSignalIds(QVariant& ids);

GetSignalIds，The parameter type for this function is the same as mine.

number = Job.GetSignalIds(*SignalIds);

Why is the pointer type passed in the last call.And how is this variable SignalIds defined, the article does not give, a little confusing.

JonB

@xiaolin
I know no more than I have written. If you cannot get dynamicCall() to work suggest you try to make the call directly via the mechanism illustrated at the end of section https://doc.qt.io/qt-6/qaxbase.html#dynamicCall using queryInterface().

hskoglund

Hi, using QVariants for ByRef (out) parameters for calling into OCX dlls are tricky at best (if you google it seems no one has got it to work).
Perhaps you could trick QAxBase by not mentioning QVariants in the call, say like this:

QVariantList params = ...
int result = object->dynamicCall("GetStagePosition(double&, double&, double&, double&, double&, double&)", params);

xiaolin

@hskoglund Thanks.
I tried, but that didn't seem to work either.

QVariant varX, varY, varZ, varT, varR, varM;

QVariantList args;
args << varX << varY << varZ << varT << varR << varM;

m_axObject->dynamicCall("GetStagePosition(double&, double&, double&, double&, double&, double&)", args);

The same error is reported

QAxBase: Error calling IDispatch member GetStagePosition: Type mismatch in parameter 0

hskoglund

To find out what how to write the call, you could try a
m_axObject->generateDocumentation();
Save the output and search for the signature for that GeStagePosition()call…

xiaolin

@JonB Thanks.
I'm going to try the queryInterface() function.