QMessageBox blocks QDialog

Question

I don't really know how to formulate my question this time...

I have my application with a QDialog as a main window. The application is getting different values like temperature, humidity and so on from a remote machine.

For development I added a group box with different widgets to simulate these values. I have different limits for throwing warnings and alarms to the user.

For example if temperature rises over 30°C then I open a QMessageBox with the request time (the application does polling at the remote machine) and the current temperature. So this is updated each request cycle.

I use the show() method to bring up the message box which keeps my application running in background. The problem now is: the focus is at the message box and nothing in my main window/ QDialog can be clicked until the message box is not accepted/ has finished.

And that's my problem: in simulation mode I want to play around with different temperature values which I can adjust by slider in the main window. How can I access these widgets/ make the message box somehow "not-blocking"?

Best regards,

Matthias

Answer 1

What you're experiencing is called "modality" of a window. By default, a QMessageBox is "application modal". This means that input to all other application windows is blocked.

To change the modality, use setWindowModality() with a value from Qt::WindowModality just before you call show(). In your case:

box->setWindowModality(Qt::NonModal);
box->show();

Answer 2

Indeed you have a modal message box which is the way QMessageBox is intended to work - ie the user is to be alerted and the ui is protected from further interaction until the user has registered the message, closed the message box and (if necessary) taken any action required in response to the message.

Now if you set the message box modality to Qt::NonModal, (remember to assign it to a variable that won't go out of scope when your application continues after popping up the messagebox) you'll be able to interact with the ui even while the message box is displayed., which I have to say is 'unusual'. If I understand your requirement you will already have the message box up - then while this is still up, you'll then want to play around with different temp values in the main window - to what effect? Until another message dialog box is produced? The message box is going to have to be discarded at some point.

Not only that, but if you show a non modal message box and then interact with the main window, you're quite likely to just have the message box disappear behind the main window, out of sight anyway.

I'd suggest that message boxes are generally treated as intended - transient, temporary modal alert boxes only and that perhaps you require a clearly visible live report/status area in your main window rather than utilizing a non-modal QMessageBox.

Hope this helps

Regards

Roger