Notification of changes to the iPhone's /Documents directory

Question

We have an app that uses file sharing. UIFileSharingEnable is set etc. and it all seems to work fine, but I'm looking for some sort of notification of when files have been added/deleted on the iPhone side. Can anyone advise?

Cheers in advance.

Answer 1

This thread on the Apple Developer Forums may be of interest, in which it is suggested that you run a kqueue in its own thread, tracking the app's Documents folder.

An Apple tech followed up with some sample code here:

- (void)kqueueFired
{
    int             kq;
    struct kevent   event;
    struct timespec timeout = { 0, 0 };
    int             eventCount;

    kq = CFFileDescriptorGetNativeDescriptor(self->_kqRef);
    assert(kq >= 0);

    eventCount = kevent(kq, NULL, 0, &event, 1, &timeout);
    assert( (eventCount >= 0) && (eventCount < 2) );

    if (eventCount == 1) {
        NSLog(@"dir changed");
    }    

    CFFileDescriptorEnableCallBacks(self->_kqRef, kCFFileDescriptorReadCallBack);
}

static void KQCallback(CFFileDescriptorRef kqRef, CFOptionFlags callBackTypes, void *info)
{
    ViewController *    obj;

    obj = (ViewController *) info;
    assert([obj isKindOfClass:[ViewController class]]);
    assert(kqRef == obj->_kqRef);
    assert(callBackTypes == kCFFileDescriptorReadCallBack);

    [obj kqueueFired];
}

- (IBAction)testAction:(id)sender
{
    #pragma unused(sender)
    NSString *              docPath;
    int                     dirFD;
    int                     kq;
    int                     retVal;
    struct kevent           eventToAdd;
    CFFileDescriptorContext context = { 0, self, NULL, NULL, NULL };
    CFRunLoopSourceRef      rls;

    docPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    assert(docPath != 0);

    NSLog(@"%@", docPath);

    dirFD = open([docPath fileSystemRepresentation], O_EVTONLY);
    assert(dirFD >= 0);

    kq = kqueue();
    assert(kq >= 0);

    eventToAdd.ident  = dirFD;
    eventToAdd.filter = EVFILT_VNODE;
    eventToAdd.flags  = EV_ADD | EV_CLEAR;
    eventToAdd.fflags = NOTE_WRITE;
    eventToAdd.data   = 0;
    eventToAdd.udata  = NULL;

    retVal = kevent(kq, &eventToAdd, 1, NULL, 0, NULL);
    assert(retVal == 0);

    assert(self->_kqRef == NULL);

    self->_kqRef = CFFileDescriptorCreate(NULL, kq, true, KQCallback, &context);
    assert(self->_kqRef != NULL);

    rls = CFFileDescriptorCreateRunLoopSource(NULL, self->_kqRef, 0);
    assert(rls != NULL);

    CFRunLoopAddSource(CFRunLoopGetCurrent(), rls, kCFRunLoopDefaultMode);

    CFRelease(rls);

    CFFileDescriptorEnableCallBacks(self->_kqRef, kCFFileDescriptorReadCallBack);
}