Always got nil value from the function in iOS - ios

Question

I'm using AFNetworking for some GET queries. But my function always returns nil value. Where I was wrong?
+ (NSString *)getRequestFromUrl:(NSString *)requestUrl {
NSString * completeRequestUrl = [NSString stringWithFormat:#"%#%#", BASE_URL, requestUrl];
__block NSString * results;
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
[manager GET:completeRequestUrl parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
results = [NSString stringWithFormat:#"%#", responseObject];
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
results = [NSString stringWithFormat:#"Error"];
}];
NSLog(#"%#", results);
return results;
}
Thx! Artem.

Answer 1

You're not seeing a result because the blocks that you pass in for success and failure run asynchronously; by the time your NSLog gets called, the web service won't have returned yet. If you move your NSLog inside of your success and failure blocks, you should see a result get output to your console.
Because of the asynchronous nature of these calls, you won't be able to simply return the value from your method. Instead, you may want to take your own block as a parameter, which you can then call when you have a result. For example:
+ (void)getRequestFromUrl:(NSString *)requestUrl withCompletion:((void (^)(NSString *result))completion
{
NSString * completeRequestUrl = [NSString stringWithFormat:#"%#%#", BASE_URL, requestUrl];
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
[manager GET:completeRequestUrl parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
NSString *results = [NSString stringWithFormat:#"%#", responseObject];
if (completion)
completion(results);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSString *results = [NSString stringWithFormat:#"Error"];
if (completion)
completion(results);
}];
}
You would then call your method like so:
[YourClass getRequestFromUrl:#"http://www.example.com" withCompletion:^(NSString *results){
NSLog(#"Results: %#", results);
}
AFNetworking's sample project has an example of using a block parameter to return a value from your web service calls: https://github.com/AFNetworking/AFNetworking/blob/master/Example/Classes/Models/Post.m

Answer 2

- (void)POST:(NSString *)URLString
parameters:(id)parameters
constructingBodyWithBlock:(void (^)(id <AFMultipartFormData> formData))block
progress:(nullable void (^)(NSProgress * _Nonnull))uploadProgress
success:(void (^)(NSURLSessionDataTask *task, id responseObject))success
failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{
[_manager POST:[NSString stringWithFormat:#"%#%#",API_HOST,URLString] parameters:parameters constructingBodyWithBlock:^(id<AFMultipartFormData> _Nonnull formData) {
block(formData);
} progress:^(NSProgress * _Nonnull uploadProgress1) {
uploadProgress(uploadProgress1);
} success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
success(task,responseObject);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
failure(task,error);
}];
}