@jsulm it worked, thanks

@Jammin44fm said in QMetaMethod::tag() problem:

It lists 6.0.0 as an affected version, but nothing more recent

Then its not yet fixed. If there is no minimal reproducer you can add one.

@Jammin44fm

It seems the solution was to use;
qRegisterMetaType<JSValue>("JSValue");

Earlier in the code to register JSValue as a meta Type.
I had already tried this, but was missing the string "JSValue" from the call.
So it seems that both the type and the string are required.

All good working now,
Hopefully it will all work in 6.5 too, as it seems Qt has removed the string variant from the SDK.

@jsulm said in QJSEngine crashes when used in multithreading program:

@mdma2 said in QJSEngine crashes when used in multithreading program:

I've found a bugreport that is similar to my problem

Did you read the comments there? Especially this one: "You have to create the engine in the same thread as the one where you are using it. And you cannot create your function in one thread and call it in a different one.".
You can't make it thread safe without changing its implementation. Is there a reason why you wantr to use it from different threads?

Yeah, there's need of evaluating JS code and accessing a QJSEngine object from different threads because of my program specificity. However there should be workaround to make it possible, like switching to the engine's thread before accessing to QJSEngine object. All I have found is using signal/slot system or QMetaObject:: invokeMethod (the last one is provided in the bugreport) to do that, but none of them work at the test code, I don't know why.

@JKSH Not applicable because I have other event sink classes.
Also, I use the SLOT string because (for the sake of keeping this post clear, I didn't demonstrate that) I have file-open scenarios too: void OnSingleSelect(const QString &file) and void OnMultiSelect(const QStringList &files). They don't share signatures, so either I need to template-ize (which doesn't work well w/ signals&slots), or to repeat and tweak the helper function.
Wait: will selectedFilter trigger setDefaultSuffix along with selectNameFilter? Didn't find evidence in the source tree.
Also again: Linux Qt 5.6.1, selectedFilter doesn't setDefaultSuffix. Call chain according to https://code.qt.io/cgit/qt/qtbase.git/plain/src/widgets/dialogs/qfiledialog.cpp :
QFileDialog::getSaveFileName -> QFileDialog::getSaveFileUrl -> QFileDialog::selectNameFilter -> QFileDialogPrivate::_q_useNameFilter, which doesn't seem to be doing the work (at least, in my case) after the user clicked OK.

@jsulm Sorry, it's my fault.
I write wrong parameters at lamda function :(;;;

We have a little more information regarding our problem.

When using Visual GDB to create a new QT project for Raspberry PI, if the toolchain folder ‘C:\SysGCC\raspberry\Qt\v5-CMake’ doesn’t exist or is empty, the QT build tools are automatically downloaded and installed. The problem we are seeing is that the build tools end up being a different version (Qt v5.15.2) than what is being used on our target Raspberry Pi platform (Qt v5.12.3). This results in the following error produced by the moc compiler indicating that its attempting to compile using the much newer header libraries.

LinuxProject1_autogen/EWIEGA46WW/moc_MainWindow.cpp:80:18: error: 'QMetaObject::SuperData' has not been declared QMetaObject::SuperData::link<QMainWindow::staticMetaObject>(), ^~~~~~~~~

LinuxProject1_autogen/EWIEGA46WW/moc_MainWindow.cpp:80:65: error: expected primary-expression before ')' token
QMetaObject::SuperData::linkQMainWindow::staticMetaObject(),

Is there anything we can set in Visual Studio or elsewhere that will insure the downloaded Qt build tools match the Qt version on the target board?

This is our development environment

Windows 10
Visual Studio 2017
Qt Visual Studio Tools Version 2.8.1.6
Visual GDB 5.6R2
Qt build tools vers 5.12.3

And we are targetting Raspberry PI OS vresion Raspbian 10.

We are working around this problem by manually copying the odler set of build tools into ‘C:\SysGCC\raspberry\Qt\v5-CMake’ before making a new project using VisualGDB. We were fortunate that we had an older set of Qt build tools on another development PC to copy these from. This is not a good long term solution for us.

@JKSH Thanks for the reply. I was actually hoping to list the QMetaObject's properties on QML, in a dynamic way. Is it possible?

One more example:

#include <QCoreApplication> #include <iostream> #include <QMetaObject> #include "example.h" #include <QDebug> #include <QMetaProperty> #include <QPointer> void gadgetExplorer(void *ptr, const char* s) { //Receives Player and access its meta-object int typeId = QMetaType::type(s); const QMetaObject *mo = QMetaType::metaObjectForType(typeId); qInfo() << "Q_GADGET: " << mo->className(); QMetaProperty mp; for(int i = 1; i < mo->propertyCount(); i++) { mp = mo->property(i); qInfo() << "Q_PROPERTY: " << mp.typeName() << "Value: " << mp.readOnGadget(ptr); if(int(mp.type()) == 1024) gadgetExplorer(ptr, mp.typeName()); } } int main(int argc, char *argv[]) { QCoreApplication a(argc, argv); qRegisterMetaType<Player>(); qRegisterMetaType<P2D>(); qRegisterMetaType<P2D*>(); Player p1; p1.setSpeed(30); p1.p2d = new P2D(); p1.p2d->setX(10.0); p1.p2d->setY(25.0); gadgetExplorer(&p1, "Player"); return a.exec(); }

gadgetExplorer() works fine for the first Q_GADGET, but for the second one the read property doesn't work. Is it possible to access the second's Q_GADGET pointer?

@raphasauer said in Is it possible to read a Q_PROPERTY with a QMetaObject pointer only?:

I only have a QMetaObject of the gadget.

To add to @kshegunov's post: All instances of your QGadget share the same QMetaObject. You can check this yourself:

Player p1; Player p2; qDebug() << "Are they the same?" << (&p1.staticMetaObject == &p2.staticMetaObject)

See also:

https://doc.qt.io/qt-5/qobject.html#staticMetaObject-var (this is written for QObjects but it also applies to QGadgets) https://doc.qt.io/qt-5/qobject.html#Q_GADGET

@Dariusz If you check the PySide documentation you will see that there is no overload taking a lambda or any function/method. There are only overloads accepting strings containing method name. So, it seems not possible with PySide.
But instead of using QApplication instance you could create your own class with methods you want to call using invokeMethod.

Hi,

AFAIR, you need to add QT += core-private to your .pro file.

@Christian-Ehrlicher Thank You!

@Yash001 You can three classes & inheritance mechanism as you mentioned. I'm keeping aside the topic of why not to inherit from QThread.

Found the error myself.
In the include dir there still was the file vtkGUISupportQtModule.h from the vtk-build included which defines

VTKGUISUPPORTQT_EXPORT __declspec(dllexport)

now its working

@SGaist said in Crashing when using QJSValue call:

Did you check whether your application has a leak ?

Yes, i have tested it for leaks. Does not seem to be the case.

Is QJSValue.call to be used externally?

Hi, and welcome to the Qt forum!

Looks like a bug to me. I think you should talk to the developers on the interest mailing list.

Cheers!

@Jakob
Switch the order of the construction of objects. When the parent's destructor runs it'll try to free its children, but since you've created it after the child (hence its destructor will be called first), it will try to delete a stack object.

@Chris-Kawa Thanks for the information provided. Then I need to re-design my implementation accordingly to this limitation.