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.