How do I fetch data from URL, using xcode 4.3.1 with NSJSONSerialization Class Reference

Question

I am trying to get my head around the NSJSONSerialization Class Reference. In the lack of a code-example at the developer.apple.com website, I´m lost. There are millions of examples all around the web with other json libaries, but I haven´t been able to get any of them to work with the latest build of xcode. (I´m running: Version 4.3.1 (4E1019) and testing on iPhone 5.0.1)

I want to fetch the data from the json file into my iphone using a button.

Lets say I get my data from the URL: http://companyurl/jsonfile.json (standard JSON-format)

The jsonfile.json looks somthing like this…;

{
  "companylist":   
[
      {
        "company":"Companyname 1",
        "telephone":"1234567890",
        "url":"http:\/\/www.companyname1.com\/",
        "category":"category 1",
        "position":"1",
      },
      {
        "company":"Companyname 2",
        "telephone":"2345678901",
        "url":"http:\/\/www.companyname2.com\/",
        "category":"category 2",
        "position":"2",
      },
      {
        "company":"Companyname 3",
        "telephone":"3456789012",
        "url":"http:\/\/www.companyname3.com\/",
        "category":"category 3",
        "position":"3",
      }
]
}

What do I write in my .h, and my .m file?

Thanks for any help! :)

Answer 1

Thanks guys. I figured it out. (...and here is what I did:)

In my .m file I added this code:

    - (IBAction)getDataFromJson:(id)sender {
        NSURL *url = [NSURL URLWithString:@"http://yourwebsite.com/jsonfile.json"];

        NSData *jsonData = [NSData dataWithContentsOfURL:url];


        if(jsonData != nil)
        {
            NSError *error = nil;
            id result = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:&error];
            if (error == nil)
                NSLog(@"%@", result);
}
}

In my .h file, I added this code:

@interface ViewController : UIViewController
- (IBAction)getDataFromJson:(id)sender;

Answer 2

NSData *data=[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://your_web_server/your_file...."]];
NSError *error=nil;
id response=[NSJSONSerialization JSONObjectWithData:data options:
                                NSJSONReadingMutableContainers error:&error]; 

NSLog(@"Your JSON Object: %@ Or Error is: %@", response, error);

NOTE: This code works on Xcode 4.2 with iOS 5.01 on simulator and 5.1 on iPad device at the moment

Answer 3

There's a great tutorial here. http://www.raywenderlich.com/5492/working-with-json-in-ios-5

Answer 4

Never ever EVER use dataWithContentsOfURL: to get server data this way. It's uncontrollable and can leave your application in an unknown state. You should, at the very minimum, be making all url calls with NSURLRequest. Better yet, if you don't support pre iOS7, use NSURLSession.

Answer 5

There is a code example in the form of the Tweeting sample app.

Answer 6

    jsonDict = [[NSDictionary alloc] init];
    data = [[NSArray alloc] init]; 

      url =[NSURLURLWithString:@"Please Type Your URL  "];


 // Parse the JSON data from the given URL
  - (void) parseJSONWithURL:(NSURL *) jsonURL
  {
// Set the queue to the background queue. We will run this on the background thread to keep
// the UI Responsive.
    dispatch_queue_t queue =    dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);

  [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;

// Run request on background queue (thread).
      dispatch_async(queue, ^{
      NSError *error = nil;

    // Request the data and store in a string.
      NSString *json = [NSString stringWithContentsOfURL:jsonURL
                                              encoding:NSASCIIStringEncoding
                                                 error:&error];
      if (error == nil){

        // Convert the String into an NSData object.
        NSData *jsonData = [json dataUsingEncoding:NSASCIIStringEncoding];

        // Parse that data object using NSJSONSerialization without options.
        jsonDict = [NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:&error];

        // Parsing success.
        if (error == nil)
        {
            // Go back to the main thread and update the table with the json data.
            // Keeps the user interface responsive.
            dispatch_async(dispatch_get_main_queue(), ^{
                [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
                data= [[jsonDict valueForKey:@"Result"] valueForKey:@"data"];
                [jsonTable reloadData];
            });
        }

        // Parsing failed, display error as alert.
        else
        {
            UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Error!" message:@"Uh Oh, Parsing Failed." delegate:nil cancelButtonTitle:@"Dismiss" otherButtonTitles:nil];

            [alertView show];
        }
    }

    // Request Failed, display error as alert.
    else
    {
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Error!" message:@"Request Error! Check that you are connected to wifi or 3G/4G with internet access." delegate:nil cancelButtonTitle:@"Dismiss" otherButtonTitles:nil];

        [alertView show];
      }
   });
  }


 // Delegate call back for cell at index path.
  - (UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
   {
   UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"MainCell"];

    if (cell == nil)
    {
      cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:@"MainCell"];
}

// Set the main label as the episode name.
   cell.textLabel.text = [[data objectAtIndex:indexPath.row] objectForKey:@"fullname"];




    NSNumber *seasonNum = [[data objectAtIndex:indexPath.row] objectForKey:@"username"];
    NSNumber *episodeNum = [[data objectAtIndex:indexPath.row] objectForKey:@"location"];
    NSMutableString *seasonEpisodeNum = [NSMutableString stringWithFormat:@"username: %@ ", seasonNum];
    [seasonEpisodeNum appendString:[NSMutableString stringWithFormat:@"location: %@", episodeNum]];
    cell.detailTextLabel.text = seasonEpisodeNum;

    return cell;
    }






  -(int) numberOfSectionsInTableView:(UITableView *) tableView
  {
   return 1;
  }


  - (int) tableView:(UITableView *) tableView numberOfRowsInSection:  (NSInteger)section
  {
return [data count];
 }

this code implement .m file

and .h file

    {
       NSDictionary *jsonDict;
       IBOutlet UITableView *jsonTable;
       NSArray *data;
       NSURL *url;
    }