Hi folks. I’m seeing something weird that I don’t understand. I have a
connection defined for the main window of my Qt Widgets app, like so:
connect(qApp, &QApplication::focusChanged, [this]() { updateUIEnabling();
});
I’m seeing a 100% reproducible crash as a result of this. When the
focusChanged signal fires, I end up in updateUIEnabling() as expected, but I
immediately crash because something about the state of things is corrupted; the
immediate symptom, according to the debugger, is that the ui pointer for my
main window is equal to 0x1 (yuck). I try to access a button,
ui->playOneStepButton, and it crashes. As I said, 100% reproducible.
The weird thing is that this does *not* happen if I change the connect
statement to this:
connect(qApp, &QApplication::focusChanged, this,
&QtSLiMWindow::updateUIEnabling);
Now, 100% of the time, there is no problem, no crash, and my app chugs along
happily. No other code changes involved. I can literally flip this connect
definition back and forth in my code and go from 100% crashing to 100% fine.
I’m pretty new to Qt and maybe I’m just being clueless somehow; but I thought
that the two definitions above would be essentially identical in their effect.
Why does the first one crash? Note that it works fine in general; it seems to
crash specifically when I open a *second* main window (which makes its own
connection to focusChanged in the same way), and then close that second main
window. Now the first main window’s connection is somehow unhappy, and the
next time I trigger the focusChanged() signal, boom. It’s as if the connection
for the second window somehow interferes with the connection for the first
window, and closing the second window leads to a corruption in the connection
state.
Naturally, I am now nervous about using the first type of connection anywhere
in my code, since I don’t understand what the issue is. Can anyone shed light
on this?
Cheers,
-B.
Benjamin C. Haller
Messer Lab
Cornell University
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