Calling native function of an iOS static library (Objective-C code) from a QT widget based application

sachin.srinath

Hi All,

I am having a simple Qt 5.4 widget based application and I am trying to call a native function (member function of an Objective-C class) that I have written. I followed the solution posted on this link : https://forum.qt.io/topic/46793/solved-using-objective-c-class-in-qt-c.
Unfortunately I am still getting the error mentioned in the above link :

symbol(s) not found for architecture ...
linker command failed with exit code 1 ...

I would like to know

If there is any standard (QT prescribed) way of calling native code from QT application (widget based).
If it is possible to call a native function from an iOS static library (from .a library and not by including the source files in QT project)

Thanks in advance...

SGaist

Hi and welcome to devnet,

You can have a look at the qtmacextras module to see how you can use Objective-C++
What symbols are missing ? Are you linking to that library properly ?

sachin.srinath

Hi,
Thanks for the reply.

Ok, I will have a look at qtmacextras
The error I am getting is - "symbol(s) not found for architecture x86_64". I am new to QT and I am not sure if I am linking the library properly. Can you please guide me on this?
Also, is it better to use QT Creator or XCode if I need to mix QT and Objective-C++ code ?

sandy.martel23

You are giving us an incomplete error message.
Look in the "Compile output" view to see what symbols are not found.

Ben Lau

@sachin.srinath said:

If there is any standard (QT prescribed) way of calling native code from QT application (widget based).

If it is possible to call a native function from an iOS static library (from .a library and not by including the source files in QT project)

It may not have a standard way of calling native code. I just made my own solution , and available at :
https://github.com/benlau/quickios/blob/master/qisystemutils.mm#L362

The native code is written in .mm file. C++ code won't be able to call them directly. Instead , all the native code registers their exported functions on a messenger class. And C++ code access those functions via the messenger class too. That make the code be able to be compiled on other platform. (e.g having a CI server in Linux , use it to run test case related to data model)

sachin.srinath

@sandy.martel23
Here is the complete error:

14:29:15: Running steps for project try1...

14:29:15: Configuration unchanged, skipping qmake step.

14:29:15: Starting: "/usr/bin/make"

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -headerpad_max_install_names -Wl,-syslibroot,/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk -mmacosx-version-min=10.7 -Wl,-rpath,/Users/BTL/Qt5.4.1_ios/5.4/clang_64/lib -o try1.app/Contents/MacOS/try1 native.o main.o mainwindow.o moc_mainwindow.o -F/Users/BTL/Qt5.4.1_ios/5.4/clang_64/lib -framework QtWidgets -framework QtGui -framework QtCore -framework DiskArbitration -framework IOKit -framework OpenGL -framework AGL

Undefined symbols for architecture x86_64:

"_NSLog", referenced from:

-[MyClass doSomething] in native.o

"OBJC_CLASS$_NSObject", referenced from:

OBJC_CLASS$_MyClass in native.o

"OBJC_METACLASS$_NSObject", referenced from:

OBJC_METACLASS$_MyClass in native.o

"___CFConstantStringClassReference", referenced from:

CFString in native.o

"__objc_empty_cache", referenced from:

OBJC_METACLASS$_MyClass in native.o

OBJC_CLASS$_MyClass in native.o

"__objc_empty_vtable", referenced from:

OBJC_METACLASS$_MyClass in native.o

OBJC_CLASS$_MyClass in native.o

ld: symbol(s) not found for architecture x86_64

clang: error: linker command failed with exit code 1 (use -v to see invocation)

make: *** [try1.app/Contents/MacOS/try1] Error 1

14:29:16: The process "/usr/bin/make" exited with code 2.

Error while building/deploying project try1 (kit: Desktop Qt 5.4.1 clang 64bit)

When executing step "Make"

14:29:16: Elapsed time: 00:00.

sachin.srinath

@Ben-Lau

Thanks for sharing the code. I will have a look at it.

SGaist

Is it me or are you trying to build something for iOS using the OS X Qt version ?

sandy.martel23

@sachin.srinath

Looks like you are not linking with Foundation. Add

LIBS += -framework Foundation

To your .pro file.

sachin.srinath

@sandy.martel23
Thanks very much. Its working fine now.

Thanks everyone for helping me.