Value of NSMutableDictionary is not changing inside the block - ios

Question

I am passing the URL in this method and getting the data as output. i want to assign a new value to nsmutabledictionary but it is not assigning the value.
-(NSDictionary*) getDatafromURL: (NSString*)url{
__block NSMutableDictionary *returnData=[[NSMutableDictionary alloc] init];
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
[manager GET:url parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
returnData=(NSMutableDictionary*)responseObject;
NSLog(#"Data 1: %#",returnData);// it is printing the data
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(#"Error: %#", error);
}];
NSLog(#"Data 2: %#",returnData);// it is not printing any data
return returnData;
}
in this above example the Data 1 is showing value successfully
Data 2 gives me empty dictionary.why it is not assigning the new value?

Answer 1

That happens because you get to the line with "Data 2" first and the block is executed only afterwards, since it is an async request. I would suggest that you change your method to something like:
- (void)getDataFromURL:(NSString *)url completionHandler:(void (^)(NSMutableDictionary *returnData, NSError *error))handler {
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
[manager GET:url parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
returnData=(NSMutableDictionary*)responseObject;
NSLog(#"Data 1: %#",returnData);// it is printing the data
handler(returnData, nil);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(#"Error: %#", error);
handler(nil, error);
}];
}
There might be some compile errors in the code I provided.
The other solution would be to do a synchronous request, in which case the block would be executed before the code that is after the block.
EDIT:
If you are choosing the first solution, you have to continue using it asynchronously. So you would call it like:
[self getDataFromURL:#"abc.com" completionHandler:^ (NSMutableDictionary *returnData, NSError *error) {
// process your dictionary and the error object
}];

Answer 2

Please check whether your Data 2 is printing before data 1? If yes, its because, the response object gets downloaded only after a certain delay. Take away the return statements. Pass the data to the dictionary to which you return the method. For eg: like
instead of
self.myDictionary = [self getDatafromURL:someURl];
to
-(void) getDatafromURL: (NSString*)url{
__block NSMutableDictionary *returnData=[[NSMutableDictionary alloc] init];
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
[manager GET:url parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
returnData=(NSMutableDictionary*)responseObject;
NSLog(#"Data 1: %#",returnData);// it is printing the data
self.myDictionary = returnData;
// Continue whatever you want to do
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(#"Error: %#", error);
}];
}
Or use the dispatch methods instead of the blocks.
like
Or use manager waitUntilFinish method below.