AFNetworking for Image Downloads, Unresponsive UI - ios

Question

I'm using AFNetworking to pull images from a URL, resize, store to disk and log the path in Core Data, then load to a table view and store . When the code executes it freezes my UI. I'm not sure if it's the download or the manipulation that's causing my troubles.
The code I'm using is below
- (void)getPhoto:(NSInteger)type forManagedObject:(MyManagedObject*)object {
// download the photo
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:object.photoUrl]];
AFImageRequestOperation *operation = [AFImageRequestOperation imageRequestOperationWithRequest:request success:^(UIImage *image) {
// MyManagedObject has a custom setters (setPhoto:,setThumb:) that save the
// images to disk and store the file path in the database
object.photo = image;
object.thumb = [image imageByScalingAndCroppingForSize:CGSizeMake(PhotoBlockCellButtonWidth, PhotoBlockCellButtonHeight)];
NSError *nerror;
if (![[DataStore sharedDataStore].managedObjectContext save:&nerror]) {
NSLog(#"Whoops, couldn't save: %#", [nerror localizedDescription]);
return;
}
// notify the table view to reload the table
[[NSNotificationCenter defaultCenter] postNotificationName:#"ReloadTableView" object:nil];
}];
[operation start];
}
And here is a sample code relevant to the setter from my managed object
- (NSString*)uniquePath{
// prepare the directory string
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
// acquire a list of all files within the directory and loop creating a unique file name
NSFileManager *fileManager = [NSFileManager defaultManager];
NSArray *existingFiles = [fileManager contentsOfDirectoryAtPath:documentsDirectory error:nil];
NSString *uniquePath;
do {
CFUUIDRef newUniqueId = CFUUIDCreate(kCFAllocatorDefault);
CFStringRef newUniqueIdString = CFUUIDCreateString(kCFAllocatorDefault, newUniqueId);
uniquePath = [[documentsDirectory stringByAppendingPathComponent:(__bridge NSString *)newUniqueIdString] stringByAppendingPathExtension:#"png"];
CFRelease(newUniqueId);
CFRelease(newUniqueIdString);
} while ([existingFiles containsObject:uniquePath]);
return uniquePath;
}
- (NSString*)saveImage:(UIImage*)image{
NSString *path = [self uniquePath];
NSData *data = UIImagePNGRepresentation(image);
[data writeToFile:path atomically:YES];
return [NSString stringWithFormat:#"file://%#",path];
}
- (void) setPhoto:(UIImage *)image {
self.photoUrl = [self saveImage:image];
}
I would like to push this to a background thread, but I'm not sure what the implications are with AFNetworking, Core Data, and Messaging in terms of thread safety. Any thought?

Answer 1

AFAIK, the way you are executing your request in incorrect:
[operation start];
you should instead add the operation to an NSOperationQueue:
NSOperationQueue* operationQueue = [[NSOperationQueue alloc] init];
[operationQueue addOperation:operation];
(you should correctly memory-manage the queue).
By doing like this, your request will be executed in an async way, it won't block the UI and you will not need to deal with multithreading.

Answer 2

Based on Matt's suggestion, I improved the UI by reworking my call as follows.
- (void)getPhoto:(NSInteger)type forManagedObject:(MyManagedObject*)object {
// download the photo
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:object.photoUrl]];
AFImageRequestOperation *operation = [AFImageRequestOperation
imageRequestOperationWithRequest:request
imageProcessingBlock:^UIImage *(UIImage *image) {
return [image imageByScalingAndCroppingForSize:CGSizeMake(PhotoBlockCellButtonWidth, PhotoBlockCellButtonHeight)];
}
cacheName:nil
success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
// MyManagedObject has a custom setters (setPhoto:,setThumb:) that save the
// images to disk and store the file path in the database
object.photo = image;
object.thumb = image;
NSError *nerror;
if (![[DataStore sharedDataStore].managedObjectContext save:&nerror]) {
NSLog(#"Whoops, couldn't save: %#", [nerror localizedDescription]);
return;
}
// notify the table view to reload the table
[[NSNotificationCenter defaultCenter] postNotificationName:#"ReloadTableView" object:nil];
}
failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {
NSLog(#"Error getting photo");
}];
[operation start];
}