objective c invisible array out of function param request

Question

I'm triyng to get array from server. But it doesn't work. I'm mean in the function everything is okay with my array but out of it it's null. How to fix?

for(int i=1; i<5; i++){

    NSString *category = [NSString stringWithFormat:@"%d",i];
    NSString *encrypt = @"encrypt=93mrLIMApU1lNM619WzZje4S9EeI4L2L";
    NSString *latitude = @"latitude=32.794044";
    NSString *longtitude = @"longitude=34.989571";
    NSString *params = [NSString stringWithFormat:@"%@&category=%@&%@&%@&area=CENTER",
                    encrypt,category,latitude,longtitude];
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setURL:[NSURL URLWithString:@"http://admin.t-club.co.il/api/get-buissness"]];
    NSData *postBody = [params dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
    [request setHTTPMethod:@"POST"];
    [request setHTTPBody:postBody];
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse * _Nullable response, NSData * _Nullable data, NSError * _Nullable connectionError)
    {
    if(!connectionError)
    {
        _myDict =[NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
        _tmpArray = [_myDict objectForKey:@"result"];
        NSLog(@"my array %@",_tmpArray);//here array isn't null
    }

    }];

    [_myArray addObjectsFromArray:_tmpArray];

     }

NSLog(@"my array %@",_tmpArray);//here is null

danh · Accepted Answer · 2017-01-31 20:05:12Z

It looks like what you're aiming for is to make several async requests in sequence. This can be done by adding a little abstraction.

First, a method that makes just one request and provides a dictionary in response of the parsed JSON result...

- (void)makeRequestWithParams:(NSString *)params completion:(void (^)(NSDictionary *, NSError *))completion {
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setURL:[NSURL URLWithString:@"http://admin.t-club.co.il/api/get-buissness"]];
    NSData *postBody = [params dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
    [request setHTTPMethod:@"POST"];
    [request setHTTPBody:postBody];

    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse * _Nullable response, NSData * _Nullable data, NSError * _Nullable connectionError) {
         if(!connectionError) {
             NSDictionary *dictionary = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
             completion(dictionary, nil);
         } else {
             completion(nil, connectionError);
         }
     }];
}

Please note that the NSURLConnnection methods have been replaced by NSSession, so this code will need to change to that soon.

Now something that calls that first method over and over. This one takes an array of request parameters as input, fills a mutable array with the dictionary results, and calls a completion block when its done...

- (void)makeManyRequestsWithParams:(NSArray *)arrayOfParams fillingArray:(NSMutableArray *)result completion:(void (^)(BOOL))completion {

    if (arrayOfParams.count == 0) return completion(YES);

    NSString *nextParams = arrayOfParams[0];
    [self makeRequestWithParams:nextParams completion:^(NSDictionary *dictionary, NSError *error) {
        if (!error && dictionary) {
            [result addObject:dictionary];
            NSArray *remainingParams = [arrayOfParams subarrayWithRange:NSMakeRange(1, arrayOfParams.count-1)];
            [self makeManyRequestsWithParams:remainingParams fillingArray:result completion:completion];
        } else {
            completion(NO);
        }
    }];
}

Finally, your original loop's job is now limited to just assembling the parameters. Once those are in an array, call to make the requests...

- (void)test {
    NSMutableArray *arrayOfParams = [NSMutableArray array];
    for(int i=1; i<5; i++){

        NSString *category = [NSString stringWithFormat:@"%d",i];
        NSString *encrypt = @"encrypt=93mrLIMApU1lNM619WzZje4S9EeI4L2L";
        NSString *latitude = @"latitude=32.794044";
        NSString *longtitude = @"longitude=34.989571";
        NSString *params = [NSString stringWithFormat:@"%@&category=%@&%@&%@&area=CENTER",
                            encrypt,category,latitude,longtitude];
        [arrayOfParams addObject:params];
    }
    NSMutableArray *result = [NSMutableArray array];
    [self makeManyRequestsWithParams:arrayOfParams fillingArray:result completion:^(BOOL success) {
        if (success) {
            NSLog(@"all done, result is %@", result);
        } else {
            NSLog(@"sadness");
        }
    }];

    // don't expect results to be ready here.  they won't be.
    // see how they are logged above in the completion block?
}

tommybananas · Accepted Answer · 2017-01-31 19:35:19Z

1

NSURLConnection sendAsynchronousRequest is asynchronous meaning it will be moved to a background thread and execution will continue without waiting for the task to complete. So by the time it gets to your bottom NSLog, the request will still be processing and the value of _tmpArray will be null.

You can use sendSynchronousRequest to have the request complete before moving on.

http://codewithchris.com/tutorial-how-to-use-ios-nsurlconnection-by-example/#synchronous

edited Jan 31, 2017 at 19:35

answered Jan 31, 2017 at 19:15

tommybananas

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3 Comments

Denis Windover Over a year ago

how can I make delay until array will be full?

danh Over a year ago

I like your original answer, but not the edit. Don't block the main with sendSynchronousRequest, especially in a loop. The OP needs advice on how to preform these requests asynchronously AND serially.

danh Over a year ago

@DenisWindover - don't block! It makes users confused and mad :-)

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