Custom Plugin Class

M4cM4rco

Hello,

I'm working on developing a plugin that includes both QML and C++ classes. Everything seems to work fine so far. However, I've run into an issue with registering an enum from one of the C++ classes. After a long search, I found a workaround - though I suspect it's not the correct approach - by registering the type directly in the constructor of the automatically generated xplugin_xPlugin.cpp file in the build directory. Given that this file is marked with a comment advising against manual edits due to it being auto-generated by CMake, I decided to attempt writing my own plugin class.

In my CMake configuration, for qt_add_qml_module, I added:

NO_GENERATE_PLUGIN_SOURCE
NO_PLUGIN_OPTIONAL

and changed the linking from Tableplugin to Table with:

target_link_libraries(ExampleProject PRIVATE Qt6::Quick Table)

I created a class and did a copy-paste from xplugin_xPlugin.cpp, including adding the global function qml_register_types_x(). However, upon running the program, I encountered a linking error pointing to

Line Q_IMPORT_QML_PLUGIN(x): undefined reference to 'qt_static_plugin_x()'.

Not knowing what qt_static_plugin_x() does, I simply added an empty function in my custom plugin class. This resolved the linking error, but then I received an access violation error:

Process finished with exit code -1073741819 (0xC0000005)

From this, I deduce that I've made several mistakes, especially regarding qt_static_plugin_x(), but I'm struggling to find helpful information online. I'm hoping you might be able to assist me. I would greatly appreciate a detailed response, and if you need any more information from me, please let me know.

Many thanks,
Marco

afalsa

@M4cM4rco said in Custom Plugin Class:

Hello Marco!

Some questions:

How did you registered the enum in your class? Is a QObject class? Did you add Q_ENUM macro to that enum?
Did you add QML_ELEMENT or QML_NAMED_ELEMENT() to that class? (In this case, if you add any macro there is no need to add a global function to register any type )
Why did you added NO_GENERATE_PLUGIN_SOURCE ? As seen in docs:

Note: When using the CMake qt_add_qml_module API, a plugin will be generated automatically for you. It will take care of type registration. You only need to write a custom plugin if you have special requirements, such as registering custom image providers. In that case, pass NO_GENERATE_PLUGIN_SOURCE to the qt_add_qml_module call to disable the generation of the default plugin.

Did you follow this? Creating C++ Plugins for QML

M4cM4rco

@afalsa, thanks for your insightful questions!

I'm working with a QObject class and utilizing the enum macro. Here's a quick look at my Test class:

#include <QObject>
#include <qDebug>

class Test : public QObject {
    Q_OBJECT
public:
    Test(QObject *parent = nullptr) {
        qDebug() << "Test created";
    }
    enum TestEnum {
        First,
        Second,
        Third,
    };
    Q_ENUM(TestEnum)
};

Your suggestion to add QML_ELEMENT was an excellent tip that hadn't crossed my mind. With that, I don't need to manually register the type, and I can directly reference it in QML as Test.Third. This approach really simplifies things and perfectly suits my needs.

I initially used NO_GENERATE_PLUGIN_SOURCE thinking it was necessary for manual enum type registration, but it turns out that's not required with your advice.

Thanks a ton for your help, afalsa! Have a fantastic day!

afalsa

@M4cM4rco

Glad to hear it!

QML macros are fantastic in this case. Just to add more extra info, you can, in fact add more macros to your class depending on your needs

QML_SINGLETON