How to pass data to the View Controller using asynchronous NSURLConnection - ios

Question

I have View Controller where I get data from web, parse Json, and pass string to another View Controller. If I use synchronous NSURLConnection, everything works just fine.
But if I switch to the asynchronous, then method (void)prepareForSegue:(UIStoryboardSegue *) calls before parsing Json data which I got from web.
Just jump over _jsonArray = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil] method. Any thoughts? Thank you in advance for your help. Here is my code:
-(void)getClothInfo {
NSString *allowedClothSizeToServer = [_foreignSizeToServer stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
NSString *getDataURL = [NSString stringWithFormat:#"http://xsdcompany.com/jsoncloth.php?foreignSize=%#",allowedClothSizeToServer];
NSURL *url = [NSURL URLWithString:getDataURL];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:#"GET"];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler: ^(NSURLResponse *response, NSData *data, NSError *connectionError) {
if (connectionError) {
[self showAlertWithMessage2:#"Server is Unavialable"];
} else {
_jsonArray = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
//Loop trough our jsonArray
for (int i=0; i<_jsonArray.count; i++) {
//Create our size object
_usSizeFromServer = [[_jsonArray objectAtIndex:i] objectForKey:#"usSizeCloth"];
}
}
}];
}
- (IBAction)getIt:(id)sender {
// Validate data
if ([self validData] == NO)
{
return;
}
[self getClothInfo];
[self showNextViewController];
}
-(void) showNextViewController {
[self performSegueWithIdentifier:#"GetCLothInfo" sender:nil];
}
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
ResultViewController *resultViewController = [segue destinationViewController];
resultViewController.foreignSizeToResult = [[NSString alloc] initWithFormat:#"%# size for %# is %#", [_pickerProcessor selectedCountry].countryName, [_pickerProcessor selectedCloth].clothName, [_pickerProcessor selectedSize].sizeName];
resultViewController.dataForUsSize = [[NSString alloc] initWithFormat:#"Your US size for %# is %#", [_pickerProcessor selectedCloth].clothName, _usSizeFromServer];
}

Answer 1

You have two options. You could call showNextViewController from the completion block inside the getClothInfo method. Or better, add a completion block parameter to your getClothInfo method and call that from the completion block for the NSURLConnection.
Something like this:
-(void)getClothInfo:(void ^(void))completion {
NSString *allowedClothSizeToServer = [_foreignSizeToServer stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
NSString *getDataURL = [NSString stringWithFormat:#"http://xsdcompany.com/jsoncloth.php?foreignSize=%#",allowedClothSizeToServer];
NSURL *url = [NSURL URLWithString:getDataURL];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:#"GET"];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler: ^(NSURLResponse *response, NSData *data, NSError *connectionError) {
if (connectionError) {
[self showAlertWithMessage2:#"Server is Unavialable"];
} else {
_jsonArray = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
//Loop trough our jsonArray
for (int i=0; i<_jsonArray.count; i++) {
//Create our size object
_usSizeFromServer = [[_jsonArray objectAtIndex:i] objectForKey:#"usSizeCloth"];
}
if (completion) {
dispatch_async(dispatch_get_main_queue(), ^{
completion();
});
}
}
}];
}
- (IBAction)getIt:(id)sender {
// Validate data
if ([self validData] == NO)
{
return;
}
[self getClothInfo:^ {
[self showNextViewController];
}];
}

Answer 2

It seems like you want your json data to be downloaded before you segue, in that case the synchronous NSURLConnection makes sense
When you make an asynchronous NSURLConnection call, it means that the subsequent code will be executed ( in this case the performSegue).
It would help if you could explain what your expected behavior is

Answer 3

Register for notification when response is obtained from the connection using
[[NSNotificationCenter defaultCenter] postNotificationName:#"ResponseObtained" object:_jsonArray];
in the second view controller add observer for notification
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(handleResponse:)
name:#"ResponseObtained"
object:nil];
You can access _jasonArray in handleResponse method with
- (void)handleResponse:(NSNotification *)notif{
NSDictionary *result = [notif object]; }