iOS call object/function from Objective-C to cpp

[Marek]

Hi All,

How to call object/function from inside Objective-C *.m file ?

On iOS I'm recording from microphone using QAudioRecorder but when call arrives, even if I discard this call, and then do stop/pause on QAudioRecorder app hangs, no error in debug, I have to kill it.
This could be related to the fact that iOS prevents microphone use when there is a call.
I have created a piece of code to get notified when call is comming in order to stop/pause QAudioRecorder hoping that I will be able to resume when call was ended/discarded
So I have this notification now, how to call some function from inside Objective-C ?
Here are my codes
cl_objc_call.h

#ifndef __CLObjCCall__
#define __CLObjCCall__

#include <stdio.h>

class CL_ObjCCall
{
  public:
    static int CL_objectiveC_Call(); 
};
#endif

cl_objc_call.mm

#include "cl_objc_call.h"
#include "cl_objc_func.h"

myCLClass* CL_obj;
int fake;

int CL_ObjCCall::CL_objectiveC_Call() {
  CL_obj=[[myCLClass alloc]init];
  [CL_obj iosCallObserver:(fake)];
  return 1;
}

cl_objc_func.h

#ifndef __CLObjCFunc__
#define __CLObjCFunc__

#import <Foundation/Foundation.h>
#import <CallKit/CXCallObserver.h>
#import <CallKit/CXCall.h>

@interface myCLClass:NSObject
  @property (nonatomic, strong) CXCallObserver *callObserver;

  -(int)iosCallObserver:(int)fake;
  -(void)iosCallObserver:(CXCallObserver *)callObserver callChanged:(CXCall *)call;
  
@end
#endif

cl_objc_func.m

#import "cl_objc_func.h"

@implementation myCLClass 
  //Your objective c code here.... 
-(int)iosCallObserver:(int)fake { 
      
    CXCallObserver *callObserver = [[CXCallObserver alloc] init];
    [callObserver setDelegate:self queue:nil];
    self.callObserver = callObserver;
      
    return 1;
}
- (void)callObserver:(CXCallObserver *)callObserver callChanged:(CXCall *)call {
    if(call.onHold) {
        NSLog(@"********** voice call onHold **********/n");
    }
    else if(call.isOutgoing == false && call.hasConnected == false && call.hasEnded == false) {
        NSLog(@"********** voice call incoming **********/n");
        //here I need to call Qt to stop recorder
    }
    else if (call.hasConnected) {
        NSLog(@"********** voice call connected **********/n");
    } else if(call.hasEnded) {
        NSLog(@"********** voice call disconnected **********/n");
    }
}

@end

calling Objective-C from Qt:

CL_ObjCCall::CL_objectiveC_Call()

Any Idea highly appreciated.
Best,
Marek

[ad1170]

You can call ObjC functions from cpp when you declare them as external (e.g. external void objC_function(void);) in your cpp file.
In your .mm file you can write this function just like a normal c function. Inside this function you can access ObjC objects.

If you want to call cpp functions from ObjC code you can do that with call back functions.
For example:
ObjC (.mm) file:

void (*ptrCallBack)(int arg) = nil; // declare a pointer to the call back function

// use this function to set the call back function (later called from cpp code)
void setCallBackFunction(void (*cbFunction)(int arg))
{
   ptrCallBack = cbFunction;
}

// write a function to call the callback function from your ObjC or Swift code
void call_CallBack(int arg)
{
  if(ptrCallBack != nil)
    ptrCallBack(arg);
}

However you must declare *external setCallBack(void (cbFunction(int arg)); in your cpp file.

In your cpp code:

myClass *ptrToMyClass = nullptr;  // init this pointer after the instantiation of myClass.

void objC_callbackFunction(int arg)
{
  // do something with arg
  // if you have a pointer to your cpp class, than you can call class member functions
  if(ptrToMyClass)
    ptrToMyClass->memberFunction(arg);
}

// call this in your cpp code to set the call back function
setCallBack(&objC_callbackFunction);

Note, this don't work with c++ class member functions.

I know, this is a little bit ugly to use this workaround with call back functions. But it works when you consider a few things like nil pointer check.

[Marek]

@ad1170 I tried to rewrite these functions to ios notation like:
-(int)iosCallObserver:(int)fake;
but still I would have to set callback from CL_ObjCCall something like this:
[CL_obj setCallBack:(&objC_callbackFunction)];

I have noticed that inside
cl_objc_func.m
I can access my Singleton

else if(call.isOutgoing == false && call.hasConnected == false && call.hasEnded == false) {
        NSLog(@"********** voice call incoming **********/n");
        //here I need to call Qt to stop recorder
        Config::get().stopRecorder()
    }

And it works, just how to call some function from Singleton to my Recorder class, easiest it would be via signal but I have error: no matching function to connect to Singleton&

In Singleton.cpp file if I define
extern "C" void stop_recorder()
then I can call this stop_recorder() function but it does not know about Recorder class

Maybe its late, but more help needed ;)

Best,
Marek

[Marek]

OK, I think I have solved this problem, but Thanks for help.
So for posterity:

I have Singleton in my application and I can call functions from Singleton inside .mm file

else if(call.isOutgoing == false && call.hasConnected == false && call.hasEnded == false) {
        NSLog(@"********** voice call incoming **********/n");
        //here I need to call Qt to stop recorder
        Config::get().stopRecorder()
    }

Then in Singleton I have void pointer and two extern functions defined

 void *pointer
extern "C" void first_function();
extern "C" void second_function();

Inside class that I need to have access to I'm initiating this pointer

Config::get().pointer=(void*)this

In Singleton cpp (which is called from .mm file, BTW I have changed cl_obj_func.m to cl_obj_func.mm without changing anything inside .m or .h file)

void Config::stopRecorder() {
    qDebug()<<"Config::stopRecorder";
    first_function();
}
void first_function() {
    second_function();
}

second_function is defined in config.h (Singleton as extern) but body is in main class

void stop_recorder2() {
    Recorder *r=(Recorder*)Config::get().recorder;
    r->stopRecorder();
}

So in short, from Singleton I call first extern function which calls second extern function from file in main class, so I have all headers included and Recorder object is known to compiler.

Best,
Marek

[ad1170]

Hi Marek,
glad to hear that your issue is solved. I've seen, i forgot the extern "C" ... in my post, sorry.
At the time where i have implemented this, I had found this way, but your way seems to be better.