QPointer to MainWindow

I'm creating a dialog window and want to know, how to pass a pointer to MainWindow to it ?

Say, I need to access a getter method from MainWindow in my dialog.

MainWindow declaration is straight from the wizard:

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

In my dialog.h:

QPointer <MainWindow> mainwindow;

In constructor:

MyDialog::MyDialog(MainWindow *mw_ptr, QWidget *parent) :
    QDialog(parent),
    ui(new Ui::SceneDialog)
..
mainwindow = mw_ptr;

This gives me the error: invalid static_cast from type 'MainWindow*' to type 'QPointer::QObjectType* {aka QObject*}'

And I don't know why.

Solution

Use object_cast to cast the pointer into the type of MainWindow and since documentation doesn't say it's safe to construct QPointer with a null pointer, you can do this safer

MainWindow* ptr = qobject_cast<MainWindow*>(mw_ptr);
if(ptr != 0)
    mainwindow = ptr;

Or an alternative way is to use signals and slots to communicate between main-window and the dialog.