CODEWITHSUNDEEP
c++windowsqt
edA-qa mort-ora-y
edA-qa mort-ora-y

Reputation: 31921

Qt QApplication::commitData, Windows shutdown, confusing documentation

I'm quite confused as to what should and should not be done in QApplication::commitData. The name implies that I should just store the state, and the docs say it should not close the application. However, the default implementation indeed closes all windows thereby closing the application. Also, if this is not the way to detect windows shutdown, I don't see any other way to tell that windows is indeed being shutdown.

There is also the related saveState. The function name means about the same and the documentation is also quite similar.

How am I supposed to properly detect when the system is being shutdown and both save my state and close my application? Is commitData indeed the correct way and just suffering from a very poor name and bad documentation?

Upvotes: 1

Views: 561

Answers (2)

bootchk
bootchk

Reputation: 2016

commitData() and saveState() may seem redundant.

But the documentation says

Futhermore, most session managers will very likely request a saved state immediately after the application has been started. This permits the session manager to learn about the application's restart policy.

Maybe that explains why the notion of 'data' and 'state' are separated. During that initial call, it would not be user friendly to interact with the user.

The default response to shutdown the application seems like a good design, because if you don't reimplement, then the safest thing to do is to close the app (as if the user had chosen the Quit action), which should also save the user's data.

Is the OS shutting down, or only the session? As far as your app should be concerned, it is only the session (since technically, the user could be logging off and the OS continues to run.) And the user might consider the app to be not 'shut down', just 'paused with data safed.'

Also consider mobile platforms like iOS, where an application seeming runs forever.

Upvotes: 0

Neox
Neox

Reputation: 2004

In my practice to detect an application shutdown I usually connect to the slot void QCoreApplication::aboutToQuit (). As it says in the docu:

The signal is particularly useful if your application has to do some last-second cleanup. Note that no user interaction is possible in this state.

So far so good this has worked for me properly

Upvotes: 1

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