QDialog: how to use question mark (?) button?

Question

By default, QDialog windows have a question mark pushbutton in the upper-right corner. When I press it, the mouse cursor is changed to the 'Forbidden' cursor, and nothing else seems to happen.

While there is lots of information generated from those who want to remove the question mark (at least three SO threads are devoted to the topic), the documentation for QDialog doesn't have anything about how to actually use it.

How do I get my application to display information when the question mark is clicked? E.g., how do I get the clicked signal from the button? Better yet, where is this button documented?

Answer 1

The other answers were a bit misleading for me, focusing only on catching the question mark event, but not explaining the normal usage.

When this button is clicked and WhatsThisMode is triggered, the elements of the dialog are supposed to give info about themselves. And if mouse hovers over an element that supports this info then the pointer will become a pointing arrow with a question mark (on Windows at least), with a tooltip message displayed on mouse click.

Here's how to achieve it in PySide:

someWidget.setWhatsThis("Help on widget")

QWhatsThis documentation for PySide and Qt5 is also available.

Answer 2

It is not a button documented by Qt. You can detect this by catching events and checking event type:

http://qt-project.org/doc/qt-5/qevent.html#Type-enum

There are different types as QEvent::EnterWhatsThisMode QEvent::WhatsThisClicked and so on. I achieved something similar to what are you looking for using event filter in mainwindow.

if(event->type() == QEvent::EnterWhatsThisMode)
    qDebug() << "click";

I saw "click" when I clicked on ? button.