Trying to understand asynchronous calls - ios

Question

I have this method
- (NSString*) createUserWithName:(NSString*)TheName
{
NSURL *URL =someUrlthatIncludesTheName
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]];
[request setHTTPMethod:#"GET"];
NSURLSession *session = [NSURLSession sharedSession];
NSURL *URL = [NSURL URLWithString:url];
NSURLSessionTask *task = [session dataTaskWithURL:URL completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if (response) {
NSError* error = nil;
NSArray *output = [NSJSONSerialization JSONObjectWithData:data
options:NSJSONReadingMutableContainers
error:&error];
myID = [[output objectAtIndex:0] objectForKey:#"UserID"];
}
}];
[task resume];
return myID;
}
and another method
-(void)doSomethingWith: (NSString*) anID
Somewhere in my code, I call these methods subsequently, like this:
[self createUserWithName:#"John"];
[self doSomethingWith:myID];
However, due to the fact that the NSURLSession in createUserWithName: is asynchronous, doSomethingWith: is fired with myID = (null).
What is the best way to approach this problem, without necessarily falling back to deprecated synchronous NSURLConnection?
Thanks in advance

Answer 1

The workflow is supposed to be
- (void)createUserWithName:(NSString*)TheName
{
NSURL *URL =someUrlthatIncludesTheName
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]];
[request setHTTPMethod:#"GET"];
NSURLSession *session = [NSURLSession sharedSession];
NSURL *URL = [NSURL URLWithString:url];
NSURLSessionTask *task = [session dataTaskWithURL:URL completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if (response) {
NSError* error = nil;
NSArray *output = [NSJSONSerialization JSONObjectWithData:data
options:NSJSONReadingMutableContainers
error:&error];
myID = [[output objectAtIndex:0] objectForKey:#"UserID"];
[self doSomethingWith:myID];
}
}];
[task resume];
}
And the call is just
[self createUserWithName:#"John"];
The method doSomethingWith: is asynchronously executed in the completion block.
Alternatively use a custom completion block
- (void)createUserWithName:(NSString *)theName completion:^(NSString *identifier)completion
{
NSURL *URL =someUrlthatIncludesTheName
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]];
[request setHTTPMethod:#"GET"];
NSURLSession *session = [NSURLSession sharedSession];
NSURL *URL = [NSURL URLWithString:url];
NSURLSessionTask *task = [session dataTaskWithURL:URL completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if (response) {
NSError* error = nil;
NSArray *output = [NSJSONSerialization JSONObjectWithData:data
options:NSJSONReadingMutableContainers
error:&error];
myID = [[output objectAtIndex:0] objectForKey:#"UserID"];
completion(myID);
}
}];
[task resume];
}
and call it with
[self createUserWithName:#"John" completion:^(NSString *identifier) {
[self doSomethingWith:identifier];
}];