Is there a way to access a member in a QMainWindow from a QDialog

bigguiness

Hello all,

The topic is probably not clear but I was not sure how to word it...

I have a app that uses a QMainWindow. In the class I have a member variable, like this:

class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget* parent = nullptr);
    ...
    void createMyDialog();
    ...
    MyData* data;    // this is the member I want to access
    ...
};

The MainWindow can create a number of QDialog objects. All of them are pretty typical, but some need to access the MainWindow::data member:

class MyDialog : public QDialog {
    Q_OBJECT
public:
    MyDialog(QWidget* parent = nullptr);
    ...
    void someMethod();    // this is the method I want to access the MainWindow::data member
    ...
};

The MainWindow creation is typical in main():

    QApplication app(argc, argv);
    MainWindow window();
    window.show();
    return app.exec();

The dialog creations are also pretty straight forward:

void MainWIndow::createMyDialog() {
    MyDialog* dlg = new MyDialog(this);
    dlg->exec();
}

In the dialog I have a need for the data that was created in the MainWindow:

void MyDialog::someMethod() {
    MyData* data = ?;   // how can I get the MainWindow:data
    // do something with the data
}

I know I can pass MyData as a parameter when creating MyDialog but was wondering if there is some other way to get it, maybe by using the QWidget* parent. Is this possible? I have one dialog that is deeper than one level away from the MainWindow. I was trying to avoid having to pass the socket to each level:

MainWindow -> SomeDialog -> AnotherDialog -> FinalDialog (this one needs MyData, the 2 above do not)

Thanks for any insight.

bigguiness

Well this worked, not sure if it's the right way to do it...

class MainWindow : public QMainWindow (
    Q_OBJECT
public:
    MainWindow(QWidget* parent = nullptr);
    ...
    MyData* getData()   { return data; }
    ...

private:
    MyData* data;
};

void MyDialog::someMethod() {
    MyData* data = qobject_cast<MainWindow *>(this->parentWidget())->getData();
    ...
}

It's a bit annoying to have to include the header for MainWindow but it seems cleaner than passing the MyData as parameter to all the dialog constructors.

I still need to check if it works for a dialog that is deeper than one parent away from the MainWindow. I'm guessing I will need the correct number of parentWidget() to get to the MainWindow.

void FinalDialog::someMethod() {
    // 1st parent is AnotherDialog
    // 2nd parent is SomeDialog
    // 3rd parent is MainWindow
    MyData* data = qobject_cast<MainWindow *>(this->parentWidget()->parentWidget()->parentWidget())->getData();
    ...
}

Regards

mpergand

@bigguiness said in Is there a way to access a member in a QMainWindow from a QDialog:

I know I can pass MyData as a parameter when creating MyDialog

That's the way to do it.

but was wondering if there is some other way to get it, maybe by using the QWidget* parent. Is this possible?

Yes, but considered as bad pratice.

MainWindow -> SomeDialog -> AnotherDialog -> FinalDialog

multi dialogs Windows-ish awfulness ...
use QWizard instead.

MyDialog* dlg = new MyDialog(this);
dlg->exec();

You create a new dialog each time, if delete on close is not set, it's a memory leak. Just create the dialog on the stack since by calling exec(), your dialog is modal.