JSON async request - ios

Question

i want to use async req to get json data, i am doing this by syncrouns already, but now requirement is change, but i am unable to modify this code to aync, beacuse i have to return NSdata
+ (NSString *)stringWithUrl:(NSURL *)url
{
// if(kShowLog)
NSLog(#"%#", url);
NSURL *newURL = [NSURL URLWithString:[NSString stringWithFormat:#"%#",url]];
NSURLRequest *urlRequest = [NSURLRequest requestWithURL:newURL
cachePolicy:NSURLRequestReloadIgnoringCacheData
timeoutInterval:1];
// Fetch the JSON response
NSData *urlData;
NSURLResponse *response;
NSError *error;
// NSOperationQueue *opQueue;
// Make synchronous request
urlData = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error];
return [[NSString alloc] initWithData:urlData encoding:NSUTF8StringEncoding];
}

Answer 1

call stringWithUrl on a 2. thread if you want to keep returning the data. (I'd go with async data
dispatch_async(dispatch_get_global_queue(), ^{
NSData *d = [self stringWithUrl:myURL];
...
//update ui
dispatch_sync(dispatch_get_main_queue(), ^{
...
});
});

Answer 2

a way that would work but is QUITE the hack (which apple employed in older APIs on the mac all the time) would be to run the runloop while waiting:
hackisch :: but wraps async in sync given the completion block runs on the same thread then the runloop
__block NSString *responseString = nil;
[NSURLConnection sendAsynchronousRequest:[NSURLRequest requestWithURL:myurl]
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
responseString = [[NSString alloc] initWithData:Data encoding:NSUTF8StringEncoding];
if(!responseString) {
responseString = #"";
}
}];
while(!responseString) {
[NSRunloop currentRunloop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.1];
}
return responseString;

Answer 3

You have to create a separate thread for this process, Synchronous call of getting json data will block your main thread.
I'm changing your code to do asynchronous operation for getting json data from web service.
+ (void)stringWithUrl:(NSURL *)url
{
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
// if(kShowLog)
NSLog(#"%#", url);
NSURL *newURL = [NSURL URLWithString:[NSString stringWithFormat:#"%#",url]];
NSURLRequest *urlRequest = [NSURLRequest requestWithURL:newURL
cachePolicy:NSURLRequestReloadIgnoringCacheData
timeoutInterval:1];
// Fetch the JSON response
NSData *urlData;
NSURLResponse *response;
NSError *error;
// NSOperationQueue *opQueue;
// Make synchronous request
urlData = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error];
dispatch_sync(dispatch_get_main_queue(), ^{
//Here you have to put your code, which you wanted to get executed after your data successfully retrived.
//This block will get executed after your request data load to urlData.
});
});
}

Answer 4

What's wrong with the Asynchronous then,
NSString *responseString;
NSOperationQueue *operation = [[NSOperationQueue alloc]init];
[NSURLConnection sendAsynchronousRequest:request queue:operation completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
NSLog(#"data %#", data);
responseString = [[NSString alloc] initWithData:Data encoding:NSUTF8StringEncoding];
}];
return responseString;