How to change window title and central widget in Qt?

Hi, I have a problem with changing window title and central widget in Qt. There is MainWindow:

class MainWindow : public QMainWindow
  {
// (...)
  QStackedWidget* widgets;
  Quiz* widget1, *widget2;
  }

and there is a class Quiz:

class Quiz : public QWidget
  {
  public slots:
    void myClicked();
  }

I wanted to change MainWindow title after clicking on button, which is a element of Quiz (and it is connected with slot myClicked).

void Quiz::myClicked()
 {
 static_cast<MainWindow>(parent).myFunction();
 }

void MainWindow::myFunction()
{
widget2 = new Quiz(this,2);
widgets->addWidget(widget2);
std::cout<<"current wdgt: " << widgets->currentIndex() << std::endl; // shows: 0
widgets->setCurrentWidget(widget2);
std::cout<<"current wdgt " << widgets->currentIndex() << std::endl; // shows: 1

setWindowTitle("newTitle");
std::cout<<"Title is " << windowTitle().toStdString() << std::endl;

}

So widgets->currentIndex shows index of new widget but nothing is changed in my window. The same problem is with window title - method windowTitle() returns new title, but title on a titlebar is old. Why? If I change title in Quiz::myClicked by:

parent->setWindowTitle("newTitle");

it works! Why it works how strange? Please help.

Solution

it works! Why it works how strange? Please help.

It is not strange. That is how the Qt API is designed. See the documentation for the explanation:

windowTitle : QString

This property holds the window title (caption).

This property only makes sense for top-level widgets, such as windows and dialogs.

Let us analyze the last sentence: your quiz is neither a QMainWindow, nor a QDialog, hence it cannot work. Windows titles only make sense for those based on the documentation. When you call it on the parent, it will work respectively since that is a QMainWindow.