QApplication and NSApplication

[MrZnuk]

Hi,
Is the QApplication implementation on macOS derive from or rely on the NSApplication class from AppKit?
And more specifialy, is the NSApplicationMain is called when calling QApplication::exec?
Thanks a lot for your help :)

[IgKh]

Welcome to the forum.

QApplication doesn't derive from NSApplication (even if it made sense, it can't - C++ classes can't inherit from Objective-C classes).

Qt is cross platform, and to achieve that it has an internal layer called QPA (Qt Platform Abstraction) that isolates the native windowing APIs behind a plugin interface.

On macOS, there is a Cocoa / AppKit based QPA plugin in use, which manages the global NSApplication behind the scenes, and links its event loop to Qt event handling. It does so by (among other things) attaching its own application delegate.

QApplication::exec usually indirectly causes the run message to be dispatched to NSApp. NSApplicationMain is bypassed as it is irrelevant - Qt applications are by definition nibless. You shouldn't call it yourself.

Hopefully this answers the question.

[MrZnuk]

Hi @IgKh,
Thanks a lot for this comprehensive response, this is much clearer now.
Regards