JSON dealy response - ios

Question

I am using JSON to get data from web service.The problem is When i call web service and due to slow response my app become unresponsive for few seconds and some times crash.
I search a lot and found that by making Asynchronous call instead of Synchronous call can solve problem. But how to use asynchronous call that i don't know.
My code is like..
SBJSON *json = [SBJSON new];
json.humanReadable = YES;
responseData = [[NSMutableData data] retain];
NSString *service = #"/Get_NearbyLocation_list";
double d1=[[[NSUserDefaults standardUserDefaults]valueForKey:#"LATITUDE"] doubleValue];
NSLog(#"%f",d1);
double d2=[[[NSUserDefaults standardUserDefaults]valueForKey:#"LONGITUDE"] doubleValue];
NSLog(#"%f",d2);
NSString *requestString = [NSString stringWithFormat:#"{\"current_Lat\":\"%f\",\"current_Long\":\"%f\"}",d1,d2];
NSLog(#"request string:%#",requestString);
// NSString *requestString = [NSString stringWithFormat:#"{\"GetAllEventsDetails\":\"%#\"}",service];
NSData *requestData = [NSData dataWithBytes: [requestString UTF8String] length: [requestString length]];
NSString *fileLoc = [[NSBundle mainBundle] pathForResource:#"URLName" ofType:#"plist"];
NSDictionary *fileContents = [[NSDictionary alloc] initWithContentsOfFile:fileLoc];
NSString *urlLoc = [fileContents objectForKey:#"URL"];
urlLoc = [urlLoc stringByAppendingString:service];
NSLog(#"URL : %#",urlLoc);
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL: [NSURL URLWithString: urlLoc]];
NSString *postLength = [NSString stringWithFormat:#"%d", [requestData length]];
[request setHTTPMethod: #"POST"];
[request setValue:postLength forHTTPHeaderField:#"Content-Length"];
[request setValue:#"application/json" forHTTPHeaderField:#"Content-Type"];
[request setHTTPBody: requestData];
// self.connection = [NSURLConnection connectionWithRequest:request delegate:self];
NSError *respError = nil;
NSData *returnData= [NSURLConnection sendSynchronousRequest: request returningResponse: nil error: &respError ];
if (respError)
{
UIAlertView *alt=[[UIAlertView alloc]initWithTitle:#"Internet connection is not Available!" message:#"Check your network connectivity" delegate:nil cancelButtonTitle:#"Ok" otherButtonTitles:nil, nil];
[alt performSelectorOnMainThread:#selector(show) withObject:nil waitUntilDone:YES];
[alt release];
[customSpinner hide:YES];
[customSpinner show:NO];
}
else
{
NSString *responseString = [[NSString alloc] initWithData:returnData encoding: NSUTF8StringEncoding];
NSLog(#" %#",responseString);
NSDictionary *results = [[responseString JSONValue] retain];
NSLog(#" %#",results);
thanks in advance..

Answer 1

NSData *returnData= [NSURLConnection sendSynchronousRequest: request returningResponse: nil error: &respError ];
this line makes the call a synchronous one.
Use this
-(void)downloadWithNsurlconnection
{
//MAke your request here and to call it async use the code below
NSURLConnection * connection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self startImmediately:YES];
}
- (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
[receivedData setLength:0];
}
- (void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[receivedData appendData:data];
}
- (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}
- (NSCachedURLResponse *) connection:(NSURLConnection *)connection willCacheResponse: (NSCachedURLResponse *)cachedResponse {
return nil;
}
- (void) connectionDidFinishLoading:(NSURLConnection *)connection {
NSLog(#"Succeeded! Received %d bytes of data",[receivedData length]);
//Here in recieved data is the output data call the parsing from here and go on
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}

Answer 2

this is how u can send asynchronous url request
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL: [NSURL URLWithString: urlLoc]];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
if ([data length] > 0 && error == nil)
//date received
else if ([data length] == 0 && error == nil)
//date empty
else if (error != nil && error.code == ERROR_CODE_TIMEOUT)
//request timeout
else if (error != nil)
//error
}];