Question

I have the following problem with Qt (no answer on this site seemed to address exactly this problem so I create my own question).

I have an application with a MainWindow class which inherits from QWidget. At a certain point there is a table inside the main window and I want to catch all mouse pressed events outside that table.

My first solution was to reimplement the method

/* virtual */ void MainWindow::mousePressEvent(QMouseEvent *event)

In this method, I check the position of the event and check that it is not within the QRect of the table. Unfortunately, I realized that mousePressEvent() is not always called. I suspect that if I click on another child widget of MainWindow, that widget consumes the event and does not pass it through to the parent.

So the only alternative idea I had was to reimplement the mousePressEvent() method for all the widgets contained in MainWindow. This is of course not feasible, because:

1. There a lot of them: it would be very complex, time-consuming, error-prone, and difficult to maintain if one had to change all the widget classes that are instantiated inside MainWindow.
2. Some of the subwidgets are implemented in some library modules developed in a parallel project, so I cannot change those.
3. In other cases, the subwidgets use Qt classes directly.
4. Even if I defined custom subclasses for 2 and 3, I would have to make sure that these subclasses are used everywhere instead of the original classes. This might imply again falling back to case 2.

So this alternative solution seems unfeasible to me.

Summarizing: Do you know if there is a simple method to catch all mouse clicks on the main window from within the MainWindow class?

Answer 1

You could do this by installing an event filter in the main window. Take a look at QObject::installEventFilter() in the Qt docs.