QFileDialog: Enable/Disable "Open" button in inherited class not working

[bmahf]

Yes, that was it. I made the following changes to my code. When I grab the Open button in the constructor, I install the event filter on that button. I overrode the eventFilter() function as shown. Fixed my problem. Thanks for the help. Now I know...

MyFileDialog::MyFileDialog(QWidget* parent, QString startdir)
   : QFileDialog(parent, tr("Load Correct Format"), startdir),
   myOpenButton(0)
{
	// constructor - on setting the myOpenButton pointer, I register
	// the event filter on that button.
    myOpenButton->installEventFilter(this);
}
 
bool MyFileDialog::eventFilter(QObject* obj, QEvent* event)
{
  if (obj == myOpenButton)
  {
	 QEvent::Type type = event->type();
	 bool valid = validSelection();
	 bool enabled = myOpenButton->isEnabled();
	 if (type == QEvent::EnabledChange && enabled && !valid)
	 {
		// don't allow QFileDialog to alter the state of the
		// Open button.  This is to be handled locally in the
		// MyFileDialog::fileSelectionChanged() function.
		myOpenButton->setEnabled(false);
		return true;
	 }
	 else
		return false;
  }
 
  // pass unfiltered events on to the parent class
  return QFileDialog::eventFilter(obj, event);
}

MyFileDialog::MyFileDialog(QWidget* parent, QString startdir)
   : QFileDialog(parent, tr("Load Correct Format"), startdir),
   myOpenButton(0)
{
	// constructor - on setting the myOpenButton pointer, I register
	// the event filter on that button.
    myOpenButton->installEventFilter(this);
}

bool MyFileDialog::eventFilter(QObject* obj, QEvent* event)
{
  if (obj == myOpenButton)
  {
	 QEvent::Type type = event->type();
	 bool valid = validSelection();
	 bool enabled = myOpenButton->isEnabled();
	 if (type == QEvent::EnabledChange && enabled && !valid)
	 {
		// don't allow QFileDialog to alter the state of the
		// Open button.  This is to be handled locally in the
		// MyFileDialog::fileSelectionChanged() function.
		myOpenButton->setEnabled(false);
		return true;
	 }
	 else
		return false;
  }

  // pass unfiltered events on to the parent class
  return QFileDialog::eventFilter(obj, event);
}

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[anda_skoa]

I would suggest to check the event type right in the first if, otherwise you are calling validSelection() for every event that the button gets.
As long as validSelection() is basically just returning a boolean that is fine either way, but if you ever change it to do something more, it becomes just unnecessary overhead.

Cheers,
_

[bmahf]

Yeah, I had updated that myself after submitting, but thanks for catching it. The actual version of the if statement is shown in the following code block. validSelection() only returns a bool that was already figured out before this point, but it's better this way, because validSelection() never gets called if the type isn't EnabledChange, and if the button isn't currently enabled:

if (obj == myOpenButton)
      {
         if (event->type() == QEvent::EnabledChange &&
             myOpenButton->isEnabled() &&
             !validSelection())
         {
            // don't allow QFileDialog to alter the state of the
            // Open button.  This is to be handled locally in the
            // MyFileDialog::fileSelectionChanged() function.
            myOpenButton->setEnabled(false);
            return true;
         }
         else
            return false;
      }

if (obj == myOpenButton)
      {
         if (event->type() == QEvent::EnabledChange &&
             myOpenButton->isEnabled() &&
             !validSelection())
         {
            // don't allow QFileDialog to alter the state of the
            // Open button.  This is to be handled locally in the
            // MyFileDialog::fileSelectionChanged() function.
            myOpenButton->setEnabled(false);
            return true;
         }
         else
            return false;
      }

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