Is it possible to share complex polymorphic objects between processes (such as [IShape=>Circle]) using D-Bus interface?

caramel_fudge

Dear Qt community!

Our use case is to pass complex polymorphic objects between two processes (for example a client and a server). D-bus seemed the perfect candidate to this scenario.

Unfortunately we are struggling to achieve this.

For this example just use Shape and derived classes such as Circle and Rectangle.

#include <QDBus
#include <memory>

class Shape {
public:
    virtual ~Shape() = default;
    virtual void draw() = 0;
};

Q_DECLARE_METADATA(Shape)

// Implemented somewhere else

class Circle : public Shape {
public:
    virtual ~Circle() {}
    virtual void draw() {
        // do the drawing
    }
};

With qtcpp2xml we generate the xml, then the adaptors and proxies. I read somewhere in the documentation that you need also add Q_DECLARE_METADATA() also in order to pass objects. Unfortunately it is not that simple. For simplicity just leave it for now, and let's continue normally.

#include <QObject>

#include <memory>
#include <vector>

class DrawingBoard : public QObject {
    Q_OBJECT
   Q_CLASSINFO("D-Bus Interface", "org.geo.DrawingBoard")

public:
    virtual ~DrawingBoard() {}

public slots:
    void addShape(std::unique_ptr<Shape> shape) {
        shapes.emplace_back(std::move(shape));
    }

    void draw()
    {
        for (auto& shape : shapes) {
            shape->draw();
        }
    }

private:
    std::vector<std::unique_ptr<Shape>> shapes;
};

Is it possible to use D-Bus like this? If it is possible, how? The code generator reports that cannot use pointers! If I change the corresponding line to reference, then the compilation will fail, because it cannot pass incomplete type!