Qt: Adding native OS Specific code to project - c++

Question

My project is a Qt application written in C++, running on Windows, OS X and Linux. There is a certain area Qt doesn't cover in its abstraction: Iterating other application windows active on the desktop, and returning their names, their 'handles' and icons.
I have OS specific code to do just that.
Pure Win32/C++ on windows
Objective-C on OS X
and some X11 c++ code for linux
I'd like to build my own abstraction that would utilize those OS Specific native snippets to provide it the runtime data it needs.
So, I'd have to have objective-C code build and run with my OS X build
Win32/c++ with windows
and similar with Linux
Let's focus on Mac, just for this example. How do I combine an objective C class into my Qt C++ project? how do I call it from C++? Are there any samples where I can see how it's done?
Ideally I would like to have the OS specific code in the project, and not build separate shared libraries to be linked in, although this is an option if nothing else can be done.

Answer 1

I suppose I would create shared libraries in this situation. Anyway, what I'm about to suggest is an idea, but should work.
By using qmake capabilities, I would create a pro file with different configurations for each platforms, where each configuration (CONFIG variable) includes different sources (this is if you don't want to use simple ifdef's. What I commonly do is create a common header, and different implementations for each platform in a different cpp files. For instance:
/* platformaspecific.h */
class PlatformSpecific : public QObject
{
PlatformSpecific(QObject* parent = 0);
QList<void*> getHandleForWindows(...);
void doSomethingPlatformIndependent();
...
};
/* platformspecific_x11.cpp */
PlatformSpecific::PlatformSpecific(QObject* parent) : QObject(parent)
{
...
}
PlatformSpecific::getHandleForWindows(...)
{
...
}
...
/* platformspecific_win.cpp */
PlatformSpecific::PlatformSpecific(QObject* parent) : QObject(parent)
{
...
}
QList<void*> PlatformSpecific::getHandleForWindows(...)
{
...
}
/* platformspecific_common.cpp (if needed) */
void PlatformSpecific::doSomethingPlatformIndependent()
...
and so on...
Then, in your .pro file, you use different scopes and include the source files according to their related CONFIG.
CONFIG += X11
X11 {
SOURCES += platformspecific_x11.cpp
}
else:WIN {
SOURCES += platformspecific_win.cpp
}
...
SOURCES += platformspecific_common.cpp
After this, for the part including Objective-C you'll have to use Objective-C++. You can mix C++ and Objective-C quite easily with Objective-C++, only some things are not allowed, like extending C++ classes with Objective-C and so on... You can find whatever you need to program using Objective-C++ in the Apple Dev Center. I don't know how good is programming in Objective-C++ using Qt Creator, but anyway you can always create a Xcode project from the .pro file using qmake: read this http://doc.qt.io/archives/qt-4.7/qtmac-as-native.html#development-tools.
By using this approach, or something similar it should be quite comfortable to work.

Answer 2

I would recommend making them static libraries and linking them in. It makes the code simple and direct. It adds the complexity to the build, but generally speaking, it is all or nothing. Once you get it working, there aren't any gotchas.
Things like preprocessor defines work, but when they break it isn't always obvious to the developer why.