Calling objective c function in callback function

Question

How to call objective c function in callback function

Callback Function:

static OSStatus inputRenderCallback (

    void                        *inRefCon,      
    AudioUnitRenderActionFlags  *ioActionFlags, 
    const AudioTimeStamp        *inTimeStamp,   
    UInt32                      inBusNumber,    
    UInt32                      inNumberFrames, 
    AudioBufferList             *ioData         
) {

    soundStructPtr    soundStructPointerArray   = (soundStructPtr) inRefCon;
    UInt32            frameTotalForSound        = soundStructPointerArray[inBusNumber].frameCount;
    BOOL              isStereo                  = soundStructPointerArray[inBusNumber].isStereo;


    AudioUnitSampleType *dataInLeft;
    AudioUnitSampleType *dataInRight;

    dataInLeft                 = soundStructPointerArray[inBusNumber].audioDataLeft;
    if (isStereo) dataInRight  = soundStructPointerArray[inBusNumber].audioDataRight;

    AudioUnitSampleType *outSamplesChannelLeft;
    AudioUnitSampleType *outSamplesChannelRight;

    outSamplesChannelLeft                 = (AudioUnitSampleType *) ioData->mBuffers[0].mData;
    if (isStereo) outSamplesChannelRight  = (AudioUnitSampleType *) ioData->mBuffers[1].mData;


    UInt32 sampleNumber = soundStructPointerArray[inBusNumber].sampleNumber;


    for (UInt32 frameNumber = 0; frameNumber < inNumberFrames; ++frameNumber) {

        outSamplesChannelLeft[frameNumber]                 = dataInLeft[sampleNumber];
        if (isStereo) outSamplesChannelRight[frameNumber]  = dataInRight[sampleNumber];

        sampleNumber++;

        if (sampleNumber >= frameTotalForSound){
            sampleNumber = 0;

        }
    }


    soundStructPointerArray[inBusNumber].sampleNumber = sampleNumber;


    return noErr;
}

Objective c function:

- (void) stopAUGraph {

    NSLog (@"Stopping audio processing graph");
    Boolean isRunning = false;
    OSStatus result = AUGraphIsRunning (processingGraph, &isRunning);
    if (noErr != result) {[self printErrorMessage: @"AUGraphIsRunning" withStatus: result]; return;}

    if (isRunning) {

        result = AUGraphStop (processingGraph);
        if (noErr != result) {[self printErrorMessage: @"AUGraphStop" withStatus: result]; return;}
        self.playing = NO;
    }
}

now in

if (sampleNumber >= frameTotalForSound){
   sampleNumber = 0;
}

of callback function part how can i call stopAUGraph function

Answer 1

A. Objects have methods, no functions. Methods are not called, but messages are sent to a receiver, that executes the method.

B. Therefore you need a reference to the instance as the receiver of the message, that leads to the execution of the method. There are two ways to get it:

B.A. Typically a callback has a userInfo pointer, which can hold the reference directly or in a structure.

B.B. If you do not have such a info, you can ask a singleton for it or use a global var. This is worse.

C. After having such a receiver reference, you can use the usual message syntax in the C function, if it is compiled as Objective-C code (filename.m or setting in Xcode):

void function (void *userInfo)
{
   id reference = userInfo; // Using ARC you have to clarify the ownership with castings.
   [reference message];
}

You can use a function call, too, if you get the implementation pointer of the method or by using the rte, for example objc_msgSend(). Getting the implementation pointer is worse, because it turns off the polymorphic mechanism.