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iOS

Posted by Thomas Nilsen
Thomas Nilsen
14,957 Points

NSURLSession is suspiciously slow

This is a duplicate post, I know, but it wouldn't let me edit it nor add the IOS tag, so:

I used the following code:

NSString *CLIENT_ID = @"SECRET";
    NSString *CLIENT_SECRET = @"SECRET";

    NSString *SEARCH = [NSString stringWithFormat:@"https://api.foursquare.com/v2/venues/search?near=gjovik&query=cafe&client_id=%@&client_secret=%@&v=20140119", CLIENT_ID, CLIENT_SECRET];

    NSURL *searchResults = [NSURL URLWithString:SEARCH];
    NSData *jsonData = [NSData dataWithContentsOfURL:searchResults];

    NSError *error = nil;
    NSDictionary *dataDictionary = [NSJSONSerialization JSONObjectWithData:jsonData options:0 error:&error];

    self.venues = dataDictionary[@"response"][@"venues"];
        [self loadAnnotationsAndCenter:YES];

This worked - no problem. But I decided to switch it up using NSURLSession. The code now looks like this:

NSString *CLIENT_ID = @"SECRET";
    NSString *CLIENT_SECRET = @"SECRET";

    NSString *SEARCH = [NSString stringWithFormat:@"https://api.foursquare.com/v2/venues/search?near=gjovik&query=cafe&client_id=%@&client_secret=%@&v=20140119", CLIENT_ID, CLIENT_SECRET];
    NSURL *URL = [NSURL URLWithString:SEARCH];
NSURLRequest *request = [NSURLRequest requestWithURL:URL];
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config];

    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
        NSDictionary *dataDictionary = (NSDictionary *)[NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
        self.venues = dataDictionary[@"response"][@"venues"];
        [self loadAnnotationsAndCenter:YES];
    }];

    [task resume];

Why is NSURLSession so much slower than the first method? We're talking as much as 10-30 seconds slower. Sometimes I get weird errors using the the second piece of code. Am I implementing something wrong?

Cheers!

3 Answers

Chase Lee
Chase Lee
29,275 Points
Chase Lee
Chase Lee
29,275 Points

Would you like me to delete your previous post?

Thomas Nilsen
Thomas Nilsen
14,957 Points

yes please

Chase Lee
Chase Lee
29,275 Points

Done. Sorry I don't have much experience with ios. Otherwise I would try to help you.

Thomas Nilsen
Thomas Nilsen
14,957 Points

No problem. Hopefully someone else will :)

J Sherwani
J Sherwani
248 Points
J Sherwani
J Sherwani
248 Points

Thomas,

Which part of the code takes the extra 10-30 seconds? Is it the callback to the completion handler? One way to debug this is through a proxy, where you can inspect exactly what network traffic is flowing through (and how long it's taking). I'd be happy to walk you through this if you're interested — I have some free time right now, and have decided to spend the rest of my evening helping out.

J

Thomas Nilsen
Thomas Nilsen
14,957 Points

Hi! Sorry for late response (time zones). The code that takes such a long time is this line inside the completion handler

[self loadAnnotationsAndCenter:YES];

Which depends on the 

self.venues arrays to be filled up

What's strange is, I have a button which takes to me to a table view, where all the different location names is displayed, meaning the self.venues array has to be complete. So I don't understand why the function [self loadAnnotationsAndCenter:YES]; takes that much time, when the array is filled up.

Thomas Nilsen
Thomas Nilsen
14,957 Points
Thomas Nilsen
Thomas Nilsen
14,957 Points

I figured it out! the loadAnnotationsAndCenter method has to run on the main thread. This code solved my problems:

dispatch_async(dispatch_get_main_queue(), ^{ 
    [self loadAnnotationsAndCenter:YES]; 
});