How to load JSON asynchronously (iOS) - ios

Question

My app parses information from a Rails app using JSON. I'm looking for a way to load the JSON asynchronously, but I'm having trouble getting my code to work with examples I have found because of the complexity of my code. What do I have to do to make my JSON load asynchronously? Thanks.
- (void)viewDidLoad
{
[super viewDidLoad];
NSURL *upcomingReleaseURL = [NSURL URLWithString:#"http://obscure-lake-7450.herokuapp.com/upcoming.json"];
NSData *jsonData = [NSData dataWithContentsOfURL:upcomingReleaseURL];
NSError *error = nil;
NSDictionary *dataDictionary = [NSJSONSerialization JSONObjectWithData:jsonData options:0 error:&error];
NSArray *upcomingReleasesArray = [dataDictionary objectForKey:#"upcoming_releases"];
//This is the dateFormatter we'll need to parse the release dates
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"];
NSTimeZone *est = [NSTimeZone timeZoneWithAbbreviation:#"EST"];
[dateFormatter setTimeZone:est];
[dateFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:#"en_US"]]; //A bit of an overkill to avoid bugs on different locales
//Temp array where we'll store the unsorted bucket dates
NSMutableArray *unsortedReleaseWeek = [[NSMutableArray alloc] init];
NSMutableDictionary *tmpDict = [[NSMutableDictionary alloc] init];
for (NSDictionary *upcomingReleaseDictionary in upcomingReleasesArray) {
//We find the release date from the string
NSDate *releaseDate = [dateFormatter dateFromString:[upcomingReleaseDictionary objectForKey:#"release_date"]];
//We create a new date that ignores everything that is not the actual day (ignoring stuff like the time of the day)
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *components =
[gregorian components:(NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit) fromDate:releaseDate];
//This will represent our releases "bucket"
NSDate *bucket = [gregorian dateFromComponents:components];
//We get the existing objects in the bucket and update it with the latest addition
NSMutableArray *releasesInBucket = [tmpDict objectForKey:bucket];
if (!releasesInBucket){
releasesInBucket = [NSMutableArray array];
[unsortedReleaseWeek addObject:bucket];
}
UpcomingRelease *upcomingRelease = [UpcomingRelease upcomingReleaseWithName:[upcomingReleaseDictionary objectForKey:#"release_name"]];
upcomingRelease.release_date = [upcomingReleaseDictionary objectForKey:#"release_date"];
upcomingRelease.release_price = [upcomingReleaseDictionary objectForKey:#"release_price"];
upcomingRelease.release_colorway = [upcomingReleaseDictionary objectForKey:#"release_colorway"];
upcomingRelease.release_date = [upcomingReleaseDictionary objectForKey:#"release_date"];
upcomingRelease.thumb = [upcomingReleaseDictionary valueForKeyPath:#"thumb"];
upcomingRelease.images = [upcomingReleaseDictionary objectForKey:#"images"];
[releasesInBucket addObject:upcomingRelease];
[tmpDict setObject:releasesInBucket forKey:bucket];
}
[unsortedReleaseWeek sortUsingComparator:^NSComparisonResult(id obj1, id obj2) {
NSDate* date1 = obj1;
NSDate* date2 = obj2;
//This will sort the dates in ascending order (earlier dates first)
return [date1 compare:date2];
//Use [date2 compare:date1] if you want an descending order
}];
self.releaseWeekDictionary = [NSDictionary dictionaryWithDictionary:tmpDict];
self.releaseWeek = [NSArray arrayWithArray:unsortedReleaseWeek];
}

Answer 1

One simple approach is to use NSURLConnection's convenient class method sendAsynchronousRequest:queue:error.
The following code snippet is an example how to load a JSON from a server, and where the completion handler executes on a background thread which parses the JSON. It also performs all recommended error checking:
NSURL* url = [NSURL URLWithString:#"http://example.com"];
NSMutableURLRequest* urlRequest = [NSMutableURLRequest requestWithURL:url];
[urlRequest addValue:#"application/json" forHTTPHeaderField:#"Accept"];
NSOperationQueue* queue = [[NSOperationQueue alloc] init];
[NSURLConnection sendAsynchronousRequest:urlRequest
queue:queue
completionHandler:^(NSURLResponse* response,
NSData* data,
NSError* error)
{
if (data) {
NSHTTPURLResponse* httpResponse = (NSHTTPURLResponse*)response;
// check status code and possibly MIME type (which shall start with "application/json"):
NSRange range = [response.MIMEType rangeOfString:#"application/json"];
if (httpResponse.statusCode == 200 /* OK */ && range.length != 0) {
NSError* error;
id jsonObject = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error];
if (jsonObject) {
dispatch_async(dispatch_get_main_queue(), ^{
// self.model = jsonObject;
NSLog(#"jsonObject: %#", jsonObject);
});
} else {
dispatch_async(dispatch_get_main_queue(), ^{
//[self handleError:error];
NSLog(#"ERROR: %#", error);
});
}
}
else {
// status code indicates error, or didn't receive type of data requested
NSString* desc = [[NSString alloc] initWithFormat:#"HTTP Request failed with status code: %d (%#)",
(int)(httpResponse.statusCode),
[NSHTTPURLResponse localizedStringForStatusCode:httpResponse.statusCode]];
NSError* error = [NSError errorWithDomain:#"HTTP Request"
code:-1000
userInfo:#{NSLocalizedDescriptionKey: desc}];
dispatch_async(dispatch_get_main_queue(), ^{
//[self handleError:error]; // execute on main thread!
NSLog(#"ERROR: %#", error);
});
}
}
else {
// request failed - error contains info about the failure
dispatch_async(dispatch_get_main_queue(), ^{
//[self handleError:error]; // execute on main thread!
NSLog(#"ERROR: %#", error);
});
}
}];
Although, it appears somewhat elaborate, IMO this is a minimalistic and still naïve approach. Among other disadvantages, the main issues are:
it lacks the possibility to cancel the request, and
there is no way to handle more sophisticated authentication.
A more sophisticated approach needs to utilize NSURLConnection delegates. Usually, third party libraries do implement it in this manner, encapsulating the a NSURLConnection request and other relevant state info into a subclass of NSOperation. You may start with your own implementation, for example using this code as a template.

Answer 2

If you just want to get this only json data, you do not need to set up a lot of things.
use the code below. Create jsonParse method which gets a NSData Object.
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
NSData *data = [[NSData alloc]initWithContentsOfURL:[NSURL URLWithString:#"http://obscure-lake-7450.herokuapp.com/upcoming.json"]];
dispatch_sync(dispatch_get_main_queue(), ^{
[self jsonParse:data];
});
});

Answer 3

Download your data async as in this answer: Object-c/iOS :How to use ASynchronous to get a data from URL?
Then run it through the json parser.

Answer 4

To generically run code in a background thread you can use this method:
dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// Code here is run on a background thread
dispatch_async( dispatch_get_main_queue(), ^{
// Code here is run on the main thread (the UI thread) after your code above has completed so you can update UI after the JSON call has completed if you need to.
});
});
But remember that Apple does not allow you to update UI elements in a background thread. Also, they do not allow you to spawn more threads from a background thread, it must be done from the main thread.

Answer 5

NSString *urlstr=#"http://itunes.apple.com/in/rss/topsongs/limit=25/json";
NSMutableURLRequest *request=[[NSMutableURLRequest alloc]initWithURL:[NSURL URLWithString:urlstr]];
[NSURLConnection sendAsynchronousRequest:request
queue:[[NSOperationQueue alloc] init]
completionHandler:^(NSURLResponse* response,
NSData* data, NSError* error)
{
NSError *myError = nil;
NSDictionary *dic1 = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:&myError];
if (myError ==nil) {
NSDictionary*feed =[dic1 objectForKey:#"feed"];
NSArray*arrayofentry =[feed objectForKey:#"entry"];
for(NSDictionary *dic2 in arrayofentry) {
requestReply=[dic2 objectForKey:#"title"];
[arr1 addObject:requestReply];
}
[self.table reloadData];
}
}];

Answer 6

Try this code:
NSURL * inkURL = [NSURL URLWithString:#"your url"];
NSURLRequest * request = [[NSURLRequest alloc]initWithURL:inkURL cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:10.0];
NSOperationQueue * queue = [[NSOperationQueue alloc]init];
[NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse * response, NSData * data, NSError * error) {
NSData * jsonData = [NSData dataWithContentsOfURL:inkURL];
NSDictionary * dataDictionary = [NSJSONSerialization JSONObjectWithData:jsonData options:0 error:&error];
self.inkArray = [dataDictionary objectForKey:#"users"];
}];