How to get pointer from QPointer?

kitfox

I'm having trouble trying to figure out how to get the wrapped pointer out of a QPointer. The below is failing to compile for me due to the method ScenePanel::scene(). What's the right way to extract the object in my QPointer so I can return it from this method?

C:\Qt\5.11.2\mingw53_32\include\QtCore\qpointer.h:86: error: invalid static_cast from type 'QObject*' to type 'Gf::Scene*'
     { return static_cast<T*>( wp.data()); }
                                        ^

My code:

class Scene : public QObject
{
    Q_OBJECT
};

class ScenePanel : public QWidget
{
    Q_OBJECT
    QPointer<Scene> _scene;
public:
    Scene* scene() { return _scene.data(); }
};

Christian Ehrlicher

I'm pretty sure the error does not come from the code above.
But why can't you return a QPointer<Scene> here instead?

kitfox

The error message itself actually points to the qpointer.h file, but the chain of error messages points back to the scene() method.

I could return a QPointer<Scene*>, but I feel that it ought to be possible to return a Scene* too. Also, I'm not sure how this will affect signals and slots if the setter takes a Scene*, but the getter returns a QPointer<Scene*>.

dheerendra

Scene is inherited from QObject ?

kitfox

Yes. It subclasses QObject.

Christian Ehrlicher

@kitfox said in How to get pointer from QPointer?:

class Scene : public QObject
{
Q_OBJECT
};

class ScenePanel : public QWidget
{
Q_OBJECT
QPointer<Scene> _scene;
public:
Scene* scene() { return _scene.data(); }
};

This code compiles perfectly - so as I said above your problem is somewhere else...

kshegunov

Are these two classes in different headers?
Please include the Scene header in the ScenePanel header and say how that goes.

JKSH

@kitfox said in How to get pointer from QPointer?:

invalid static_cast from type 'QObject*' to type 'Gf::Scene*'

What is Gf?

kitfox

@kshegunov You're right. They were in separate files. I was just using class Scene; to declare the class, but once I included the header instead I was able to compile.

kitfox

@JKSH A namespace I'm using. Didn't include it in my sample code.