Handling File System Events in OSX - objective-c

Question

So im using the EventStream to watch a folder for change. Now it all works fine and I can see a log call back when I alter files in the folder, but I cant seem to call my folderWatch, it gives the error "use of undeclared identifier 'self'". I can use this function everywhere else, just not in the fsEventsCallback. Any help would be appreciated!
void fsEventsCallback(ConstFSEventStreamRef streamRef,
void *clientCallBackInfo,
size_t numEvents,
void *eventPaths,
const FSEventStreamEventFlags eventFlags[],
const FSEventStreamEventId eventIds[]){
[self folderWatch];
NSLog(#"2");
}

Answer 1

The reason is that fsEventsCallback is a C function and not an Objective-C instance method, so fsEventsCallback does not know anything about self.
You can use the info field in the FSEventStreamContext to pass self to the callback function. The following example assumes that your class is called Watcher.
(If you don't use ARC, you can omit all the __bridge casts.)
- (void)folderWatch
{
}
void fsEventsCallback(ConstFSEventStreamRef streamRef,
void *info,
size_t numEvents,
void *eventPaths,
const FSEventStreamEventFlags eventFlags[],
const FSEventStreamEventId eventIds[])
{
Watcher *watcher = (__bridge Watcher *)info;
[watcher folderWatch];
}
- (void)startWatching
{
FSEventStreamContext context;
context.info = (__bridge void *)(self);
context.version = 0;
context.retain = NULL;
context.release = NULL;
context.copyDescription = NULL;
NSArray *pathsToWatch = #[#"/path/to/watch"];
self.eventStream = FSEventStreamCreate(NULL,
&fsEventsCallback,
&context,
(__bridge CFArrayRef)(pathsToWatch),
kFSEventStreamEventIdSinceNow,
1.0,
kFSEventStreamCreateFlagFileEvents
);
}