Question

Witht QtCreator set up as default when you create a widget the class for it creates the form as private to the class. So you have for example something like this:

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

//...

private:
    Ui::MainWindow *ui;
};

Now what I want to know is how you connect to the signals within the ui. For example if this widget was embedded into a QStackedWidget and when a button is pressed the page displayed needs to change. I would have considered connecting to the button but ui is private so I cannot.

Do I have to create signals in MainWindow and then within that connect the ‘ui’ signals to them and thus bubble up the hierarchy? Or have I missed something simple?

Answer 1

You can’t have an unrelated object connect to signals/slots of aggregate components, even if you could it would break encapsulation and become a maintenance nightmare.

You need to expose the signals/slots of the aggregate components by adding them to the MainWindow API, and then call the relative ui component method in the definition.

For example, in the MainWindow definition, add:

signals:
    void buttonClicked();

And then in constructor, do:

connect( ui->button, SIGNAL( clicked() ), this, SIGNAL( buttonClicked() ) );

This way, your MainWindow class propagates signals from it’s aggregates – but finetuned to exactly how you intend the class to be used.