Sending NSData to peers with MultiPeer framework - ios

Question

I have successfully implemented the multiPeer framework into my app and can easily pass images and strings to other devices. My problem is when I try to pass an NSArray converted to NSData. When the multipeer didReceiveData data func is called i always the following crash:
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSKeyedUnarchiver initForReadingWithData:]: incomprehensible archive
So heres how I send the data:
var myNSData: NSData = NSKeyedArchiver.archivedDataWithRootObject(arrayOfNumbers)
var error : NSError?
self.session.sendData(myNSData, toPeers: self.session.connectedPeers,
withMode: MCSessionSendDataMode.Reliable, error: &error)
if error != nil {
print("Error sending data: \(error?.localizedDescription)")
}
this is how I have tried to recieve the data:
func session(session: MCSession!, didReceiveData data: NSData!,
fromPeer peerID: MCPeerID!) {
// Called when a peer sends an NSData to us
// This needs to run on the main queue
dispatch_async(dispatch_get_main_queue()) {
// can't convert data back NSArray without crash
var receivedArray:NSArray = NSKeyedUnarchiver.unarchiveObjectWithData(data) as! NSArray

Answer 1

It's true that you haven't provided all the relevant code needed to ascertain the problem; however, I can say this: (1) your approach with respect to using an array makes no sense. I can provide the perfect image-broadcasting code, if you'd like; and, (2) try encoding the array using NSValue, and then archiving the NSValue object.
It's true that you haven't provided all the relevant code needed to ascertain the problem; however, I can say this: (1) your approach with respect to using an array makes no sense. I've provided you with the perfect image-broadcasting code below; and, (2) try encoding the array using NSValue, and then archiving the NSValue object.
Here's the best way to do it:
On the iOS device sending the image data:
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
CVPixelBufferLockBaseAddress(imageBuffer,0);
uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
CGImageRef newImage = CGBitmapContextCreateImage(newContext);
UIImage *image = [[UIImage alloc] initWithCGImage:newImage scale:1 orientation:UIImageOrientationUp];
CGImageRelease(newImage);
CGContextRelease(newContext);
CGColorSpaceRelease(colorSpace);
CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
if (image) {
NSData *data = UIImageJPEGRepresentation(image, 0.7);
NSError *err;
[((ViewController *)self.parentViewController).session sendData:data toPeers:((ViewController *)self.parentViewController).session.connectedPeers withMode:MCSessionSendDataReliable error:&err];
}
}
On the iOS device receiving the image data:
typedef struct {
size_t length;
void *data;
} ImageCacheDataStruct;
- (void)session:(nonnull MCSession *)session didReceiveData:(nonnull NSData *)data fromPeer:(nonnull MCPeerID *)peerID
{
dispatch_async(self.imageCacheDataQueue, ^{
dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER);
const void *dataBuffer = [data bytes];
size_t dataLength = [data length];
ImageCacheDataStruct *imageCacheDataStruct = calloc(1, sizeof(imageCacheDataStruct));
imageCacheDataStruct->data = (void*)dataBuffer;
imageCacheDataStruct->length = dataLength;
__block const void * kMyKey;
dispatch_queue_set_specific(self.imageDisplayQueue, &kMyKey, (void *)imageCacheDataStruct, NULL);
dispatch_sync(self.imageDisplayQueue, ^{
ImageCacheDataStruct *imageCacheDataStruct = calloc(1, sizeof(imageCacheDataStruct));
imageCacheDataStruct = dispatch_queue_get_specific(self.imageDisplayQueue, &kMyKey);
const void *dataBytes = imageCacheDataStruct->data;
size_t length = imageCacheDataStruct->length;
NSData *imageData = [NSData dataWithBytes:dataBytes length:length];
UIImage *image = [UIImage imageWithData:imageData];
if (image) {
dispatch_async(dispatch_get_main_queue(), ^{
[((ViewerViewController *)self.childViewControllers.lastObject).view.layer setContents:(__bridge id)image.CGImage];
dispatch_semaphore_signal(self.semaphore);
});
}
});
});
}
The reason for the semaphores and the separate GCD queues is simple: you want the frames to display at equal time intervals. Otherwise, the video will seem to slow down at first at times, right before speeding up way past normal in order to catch up. My scheme ensures that each frame plays one after another at the same pace, regardless of network bandwidth bottlenecks.