How to inherit from Qt classes whos parent is not QObject

[angus-3d]

I am trying the following

#[cxx_qt::bridge]
pub mod qobject {
    unsafe extern "C++" {
        include!(< QQuick3DInstancing >);
        type QQuick3DInstancing;
        include!("cxx-qt-lib/qbytearray.h");
        type QByteArray = cxx_qt_lib::QByteArray;
    }

    unsafe extern "RustQt" {
        #[qobject]
        #[qml_element]
        #[base = QQuick3DInstancing]
        type PointsInstancing = super::PointsInstancingRust;
    }

    unsafe extern "RustQt" {
        #[cxx_override]
        #[cxx_name = "getInstanceBuffer"]
        unsafe fn get_instance_buffer(
            self: Pin<&mut PointsInstancing>,
            instance_count: *mut i32,
        ) -> QByteArray;
    }

// etc

The problem is that QQuick3DInstancing takes a QtQuick3DObject* as a parent.

cxxqtgen/src/points_instancing.cxxqt.cpp:254:26: error: invalid conversion from 'QObject*' to 'QQuick3DObject*' [-fpermissive]
  cargo:warning=  254 |     : QQuick3DInstancing(parent),
  cargo:warning=      |                          ^~~~~~
  cargo:warning=      |                          |
  cargo:warning=      |                          QObject*

Is there any way i can use the Constructor tell it the type of the parent?

[LeonMatthesKDAB]

Hi @angus-3d ,
yes, you can use the cxx_qt::Constructor trait to implement a custom constructor in Rust.
This will then overwrite the default constructor generated by CXX-Qt.

Take a look at:
https://docs.rs/cxx-qt/latest/cxx_qt/trait.Constructor.html
and the example here:
https://github.com/KDAB/cxx-qt/blob/0.7.x/examples/qml_features/rust/src/custom_parent_class.rs

(note: This uses the shorthand cxx_qt::Initialize to simply omit the parent from the constructor)

[angus-3d]

Thank you!