Unexpected raise() behavior

Joel Bodenmann

I have a method in my MainWindow subclass that creates a new QDockWidget. That newly created dock widget is added to an existing dock widget to tabify them by using QMainWindow::tabifyDockWidget() and so far everything works.
I have another method that calls QWidget::raise() on one of the tabs of the dock widget group and the tab is successfully raised to the foreground (-> becomes the selected tab).
The next thing I wanted to do is calling the raise() method right after I added to the newly created dock widget to the dock widget group. Hence my code looks like this:

void MainWindow::createDock()
{
    // Find an existing dock that contains viewers
    QDockWidget* existingDock = nullptr;

    ...

	// Create a new dock
	QDockWidget* dock = new QDockWidget(this);
	addDockWidget(Qt::LeftDockWidgetArea, dock);

	// Tab them together
	if (existingDock) {
	    tabifyDockWidget(existingDock, dock);
	} else {
	    existingDock = dock;
	}

	// Focus the new dock
	dock->raise();
	dock->setFocus();
}

But the newly created dock is never being focused/raised.
The next thing I did was adding a single shot timer that calls another method that calls the raise() method:

void MainWindow::createDock()
{
    // Find an existing dock that contains viewers
    QDockWidget* existingDock = nullptr;

    ...

	// Create a new dock
	QDockWidget* dock = new QDockWidget(this);
	addDockWidget(Qt::LeftDockWidgetArea, dock);

	// Tab them together
	if (existingDock) {
	    tabifyDockWidget(existingDock, dock);
	} else {
	    existingDock = dock;
	}

	// Focus the new dock
	QTimer::singleShot(1, this, SLOT(highlightDock()));
}

void MainWindow::highlightDock()
{
    dock->raise();
    dock->setFocus();
    dock->highlight();
}

And that actually works - I get the expected behavior.

I am having a hard time understanding what is going on. Obviously there must be something that prevents me from raising a widget that was just added but I don't understand what it is. Can somebody enlighten me?

mrjj

Hi
Since it works if asked slightly later.
Could you try to insert
qApp->processEvents();
just before raise?
Just for test. should not matter.
But i like to test :)

Joel Bodenmann

Well that works. Might somebody explain what's going on? :) Seems like I am missing a basic concept of Qt.

SGaist

Hi,

Wild educated guess: you are calling raise right after creating a new widget but the event loop didn't got to run before you called raise thus you are calling raise on a yet to be shown widget.

Using the QTimer, you allow the event loop to run before calling raise, and it can then setup/show the widget.

Joel Bodenmann

Thank you for the help & the explanation. Very appreciated.