Parsing JSON Response from Web service to NSDictionary in iOS – Objective C

• Download sample - 34.5 KB

Introduction

This post will show how to parse the JSON response received from a web service into an NSDictionary object. For the purpose of this post, I’ll use a sample web service hosted by jsontest.com that returns the MD5 hash of the entered sample text.

The URL of the sample web service is http://md5.jsontest.com/?text=AmoghNatu.

The output when a request is made to the above URL is as shown below:

{
   "md5": "1e559716c8590f85d81abf7abff073aa",
   "original": "AmoghNatu"
}

In the sample project, I’ll display the MD5 text in an alert box.

For parsing the response JSON, we use the NSJSONSerialization class’s JSONObjectWithData method. When a request is posted to the web service, the response is initially stored in an NSData object. This NSData object is passed to JSONObjectWithData method as parameter along with json reading options and an error object, in case there is an error while parsing the JSON.

Let’s have a look at the code.

- (NSDictionary *)parseJsonResponse:(NSString *)urlString
{
    NSError *error;
    NSURL *url = [NSURL URLWithString:urlString];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request setHTTPMethod:@"GET"];
    [request setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
    
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse: nil error:&error];
    if (!data)
    {
        NSLog(@"Download Error: %@", error.localizedDescription);
        UIAlertView *alert =
        [[UIAlertView alloc]initWithTitle:@"Error"
                                  message:[NSString stringWithFormat:@"Error : %@",error.localizedDescription]
                                 delegate:self
                        cancelButtonTitle:@"Ok"
                        otherButtonTitles:nil];
        [alert show];
        return nil;
    }
    
    // Parsing the JSON data received from web service into an NSDictionary object
    NSDictionary *JSON =
    [NSJSONSerialization JSONObjectWithData: data
                                    options: NSJSONReadingMutableContainers
                                      error: &error];
    return JSON;
}

The method parseJsonResponse is a sample method that I have written that makes a request to the web service and gets the response in JSON. This JSON is then parsed into an NSDictionary object.

I have uploaded a sample application. The same can be downloaded from here too. Check that if required.

Hope this helps!