Get response from server with a custom class - ios

Question

I want to implement the following: Have a custom class(so i can call/use it from many parts of my app) where with the help of AFNetworking,i request to the server and get the response.
My code inside the class works,but when i call it from other parts of my app,i am getting a null value. I believe it because of my custom class.Anyway here is my code:
UDIDGen.h
#import <Foundation/NSString.h>
#interface NSString (UDIDGen)
+ (NSString *)getUDID;
#end
UDIDGen.m
#import "UDIDGen.h"
#import "AFHTTPClient.h"
#import "AFHTTPRequestOperation.h"
#implementation NSString (UDIDGen)
+ (NSString *)getUDID{
__strong __block NSString *holder;
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:[NSURL URLWithString:#"http://domain.com/id.php"]];
NSMutableURLRequest *request = [httpClient requestWithMethod:#"GET"
path:#"http://domain.com/id.php"
parameters:nil];
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
[httpClient registerHTTPOperationClass:[AFHTTPRequestOperation class]];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
holder=[NSString stringWithFormat:#"%#",[[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding]];
NSLog(#"SERVER RESPONSE: %#",holder);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
}];
[operation start];
return holder;
}
#end
And then when i want to call it from other parts of my app i
#import "UDIDGen.h"
and then
NSString *wsa=[NSString getUDID];
NSLog(#"Response %#",wsa);
For some reasong NSLog(#"SERVER RESPONSE: %#",holder); works and i am able to nslog the server response. But NSString *wsa=[NSString getUDID]; gives me null value.
I believe it has to do with the way i am implementing my custom class, i am doing something wrong.
Any help?
EDIT:My working code so other will use it:
UDIDGen.h
#import <Foundation/NSString.h>
#interface UDIDGen:NSObject{
}
- (void)getUDIDWithCompletion:(void (^)(NSString *udid))completion;
#end
UDIDGen.m
#import "UDIDGen.h"
#import "AFHTTPClient.h"
#import "AFHTTPRequestOperation.h"
#implementation UDIDGen
- (void)getUDIDWithCompletion:(void (^)(NSString *udid))completion {
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:[NSURL URLWithString:#"http://domain.com/id.php"]];
NSMutableURLRequest *request = [httpClient requestWithMethod:#"GET"
path:#"http://domain.com/id.php"
parameters:nil];
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
[httpClient registerHTTPOperationClass:[AFHTTPRequestOperation class]];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
NSString *udid=[[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding];
NSLog(#"SERVER RESPONSE: %#",udid);
if (completion)
{
completion(udid);
}
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
// TODO: Handle error
}];
[operation start];
}
#end
Use it like this:
UDIDGen *getResponse = [[UDIDGen alloc] init];
[getResponse getUDIDWithCompletion:^(NSString *udid) {
NSLog(#"SERVER RESPONSE: %#",udid);
}];

Answer 1

You're starting the AFHTTPRequestOperation asynchronously. This means it's running in a separate non-blocking thread, and your method might return before the request has finished.
The easiest way would be to just do this, but this will most likely block the GUI while loading:
[operation startSynchronous];
The cleanest way would be to use a completion block or delegate yourself and inform the target class when a response has been received:
+ (void)getUDIDWithCompletion:(void (^)(NSString *udid))completion {
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:[NSURL URLWithString:#"http://domain.com/id.php"]];
NSMutableURLRequest *request = [httpClient requestWithMethod:#"GET"
path:#"http://domain.com/id.php"
parameters:nil];
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
[httpClient registerHTTPOperationClass:[AFHTTPRequestOperation class]];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
NSString *udid=[[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding];
NSLog(#"SERVER RESPONSE: %#",udid);
if (completion)
{
completion(udid);
}
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
// TODO: Handle error
}];
[operation start];
}
You would call this method like so:
[YourCustomClass getUDIDWithCompletion:^(NSString *udid) {
// use udid / update GUI
}];