QT/C++ Access QLineEdit/ QTextArea functions using QWidget

Question

I'm trying to write a function, which gets a List containing some QWidget's from the UI. The function should take each widget, detect its Class and do some checks.
The Problem is, that I don't really know how to access e.g. the QLineEdit's functions when I'm in fact dealing with QWidget.
Is there a way to get this working? Or is there another completely different approach?

bool CLASS::inputValid(QList<QWidget *> widgetList) {
bool everythingValid = true;

foreach (QWidget *widget, widgetList) {
  if (QString(widget->metaObject()->className()) == "QLineEdit") {
      // check if text is empty
         if(widget->text()->length() == 0)  // I know this doesn't work this way
         everythingValid = false;
  }

  else if (QString(widget->metaObject()->className()) == "QTextEdit") {
      // check if text is empty
          if(widget->text()->length() == 0) // I know this doesn't work this way
          everythingValid = false;
  }
}

return everythingValid;

}