How to define multiple inheritance (i.e. QObject + another class)

[haata]

I'm still pouring over the source code to see if multiple inheritance is possible with the macros.

Trying to replicate this

  class OpenRGBSamplePlugin : public QObject, public OpenRGBPluginInterface
  {
      Q_OBJECT
      Q_PLUGIN_METADATA(IID OpenRGBPluginInterface_IID)
      Q_INTERFACES(OpenRGBPluginInterface)

This doesn't seem sufficient

    #[cxx_qt::qobject(base = "OpenRGBPluginInterface", qml_uri = "com.kdab.cxx_qt.demo", qml_version = "1.0")]
    #[derive(Default)]
    pub struct OpenRGBSamplePlugin {}

[ahayzen-kdab]

Thanks for taking the time to report this issue.

With the current and the 0.6 API we don't yet support specifying

• Multiple bases
• Q_INTERFACES
• Q_PLUGIN_METADATA

The way to workaround this for now would be to create a C++ class that has both the base classes and the metadata you can't specify in CXX-Qt yet. Then inherit from that combined C++ class in Rust.

class OpenRGBSampleCombined : public QObject, public OpenRGBPluginInterface
{
      Q_OBJECT
      Q_PLUGIN_METADATA(IID OpenRGBPluginInterface_IID)
      Q_INTERFACES(OpenRGBPluginInterface)
...
};

Then in Rust inherit from that C++ class

   unsafe extern "C++" {
        include!("cpp/combinedheader.h");
    }

    #[cxx_qt::qobject(base = "OpenRGBSampleCombined", qml_uri = "com.kdab.cxx_qt.demo", qml_version = "1.0")]
    #[derive(Default)]
    pub struct OpenRGBSamplePlugin {}

or for 0.6 something like

unsafe extern "C++" {
    include!("cpp/combinedheader.h");
}

extern "RustQt" {
    #[qobject] 
    #[qml_element]
    #[base_class = "OpenRGBSampleCombined"]
    type OpenRGBSamplePlugin = super::OpenRGBSamplePluginRust;
}

@LeonMatthesKDAB we should consider if we want to support things like Q_INTERFACES https://doc.qt.io/qt-6/qobject.html#Q_INTERFACES and Q_PLUGIN_METADATA https://doc.qt.io/qt-6/qtplugin.html#Q_PLUGIN_METADATA and multiple bases etc