Asynchronously Api calls and returning data outside the block - objective-c

Question

I don't understand why I am getting null array outside the block code, even though I am using __block keyword on my array.
I am successfully getting data from a backend api with following code
`-(void)getJsonResponse:(NSString *)urlStr success:(void (^)(NSArray *responseDict))success failure:(void(^)(NSError* error))failure
{
NSURLSession *session = [NSURLSession sharedSession];
NSURL *url = [NSURL URLWithString:urlStr];
// Asynchronously API is hit here
NSURLSessionDataTask *dataTask = [session dataTaskWithURL:url
completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
// NSLog(#"%#",data);
if (error)
failure(error);
else {
NSArray *json = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
// NSLog(#"%#",json);
success(json);
}
}];
[dataTask resume]; // Executed First
}`
Then in my function for returning the data I am using following
`- (NSArray *)get_data:(NSDictionary *)credentials{
NSString *urlStr =[ NSString stringWithFormat:#"http://test.com %#",credentials];
__block NSArray *jsonArray= [[NSArray alloc]init];
[self getJsonResponse:urlStr success:^(NSArray *responseArray) {
jsonArray = responseArray;
NSLog(#"%#",responseArray);
} failure:^(NSError *error) {
// error handling here ...
}];
NSLog(#"%#",jsonArray);
return jsonArray;
}
`
The issue here is although I am successfully getting data within getJsonResponse block, but when I am trying to return the response data array as function return I am getting null for jsonArray. I thought assigning __block infront of jsonArray should retain the data assign within the block code ?
The second approach is not to use Async way like following
`- (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse **)response error:(NSError **)error
{
NSError __block *err = NULL;
NSData __block *data;
BOOL __block reqProcessed = false;
NSURLResponse __block *resp;
[[[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData * _Nullable _data, NSURLResponse * _Nullable _response, NSError * _Nullable _error) {
resp = _response;
err = _error;
data = _data;
reqProcessed = true;
}] resume];
while (!reqProcessed) {
[NSThread sleepForTimeInterval:0];
}
*response = resp;
*error = err;
return data;
}`
That way its blocking the main thread whilst waiting for data.

Answer 1

I would suggest using the same approach of getJsonResponse for your get_data function:
- (void)get_data:(NSDictionary *)credentials finish:(void(^)(NSArray *data))finish{
NSString *urlStr =[ NSString stringWithFormat:#"http://test.com %#",credentials];
__block NSArray *jsonArray= [[NSArray alloc]init];
[self getJsonResponse:urlStr success:^(NSArray *responseArray) {
jsonArray = responseArray;
if (finish) {
finish(jsonArray);
}
} failure:^(NSError *error) {
// error handling here ...
}];
}