iPhone Currency Converter using Google RESTful services

Google providing REST URI for currency calculator

 http://www.google.com/ig/calculator?hl=en&q=10USD=?INR

We have to pass the above two arguments to get JSON result

{lhs: "10 U.S. dollars",rhs: "536.912752 Indian rupees",error: "",icc: true}

The above returned JSON is invalid so convert into a valid JSON by adding '"' to lhs , rhs, error and icc.

How to handle JSON in iOS5 and later:

            NSJSONSerialization class used to convert JSON to Foundation objects like NSDictionary, NSArray etc and vice versa. It is only available iOS5 and above.

 NSDictionary* json = [NSJSONSerialization 

                          JSONObjectWithData:data 

                          options:kNilOptions 

                          error:&error];  //data is NSData sent from google server

now get the resulted json in NSDictionary then we can get the result by giving the key.

 NSString* convertedvalue = [json objectForKey:@"rhs"]; 

Difference between NSURLConnection and NSData initWithContentsOfURL :-

NSURLConnection is a asynchronous request by default , it will start a thread automatically and delegates are called from that thread. 

Also NSURLConnection has a convenience class method, sendSynchronousRequest:returningResponse:error:, to load a URL request synchronously.

NSData initWithCOntentsOfURL is a synchronous method call ,so it will block the thread.

Better use dispatch_async block to run the code in separate thread, once operation completed call the main thread.

find the iphone currency converter source code :-  https://github.com/karthikprabhuA/CurrencyConverter-GoogleRESTAPI

iphone
Currency converter 

- (IBAction)convertButtonCLicked:(UIButton *)sender {

    

     if([self.progressIndicator isAnimating]  == NO)

     {

    if(self.amountTxtField.text.length > 0 && self.fromTxtField.text.length >0 && self.toTxtField.text.length > 0)

    {

        [self.progressIndicator startAnimating];

        

        dispatch_queue_t downloadQueue = dispatch_queue_create("google downloader", NULL);

        

    dispatch_async(downloadQueue, ^{

        

        NSString* amount =self.amountTxtField.text;

        NSString *fromstr = self.fromTxtField.text ;

        NSRange fromrange ;

        fromrange.length = 3;

        fromrange.location = fromstr.length - 4;

        fromstr = [fromstr substringWithRange:fromrange];

        

        NSString *tostr = self.toTxtField.text ;

        NSRange torange ;

        torange.length = 3;

        torange.location = tostr.length -4;

        tostr = [tostr substringWithRange:torange];

        

        NSString *urlAddress = [[NSString alloc] initWithFormat:GOOGLERESTURL,[NSString stringWithFormat:@"%@%@",amount,fromstr],tostr];

        NSString* escapedUrlString =

        [urlAddress stringByAddingPercentEscapesUsingEncoding:

         NSUTF8StringEncoding];

    

        NSData* data = [NSData dataWithContentsOfURL: 

                        [NSURL URLWithString:escapedUrlString]];

        [self performSelectorOnMainThread:@selector(updateConvertedValue:) 

                               withObject:data waitUntilDone:YES];

        

    });

        dispatch_release(downloadQueue);

    }

    else {

        [self alertMessage:@"Enter all values !"];

    }

     }

}

-(void)updateConvertedValue: (NSData*)receivedData

{

    NSString *result = [[NSString alloc] initWithBytes:[receivedData bytes] length:[receivedData length] encoding:NSUTF8StringEncoding];

    NSError *error = NULL;

    //google is not sending valid JSOn so convert into valid JSON

    NSString *resultdata = result;

    resultdata = [resultdata stringByReplacingOccurrencesOfString:@"{" withString:@"{\""];

     resultdata = [resultdata stringByReplacingOccurrencesOfString:@"," withString:@",\""];

     resultdata = [resultdata stringByReplacingOccurrencesOfString:@":" withString:@"\":"];

    NSData* data = [resultdata dataUsingEncoding:NSUTF8StringEncoding];

    NSDictionary* json = [NSJSONSerialization 

                          JSONObjectWithData:data 

                          options:kNilOptions 

                          error:&error];

    

    NSString* convertedvalue = [json objectForKey:@"rhs"]; 

    if(error == nil)

        outputLabel.text = convertedvalue;

    else {

        outputLabel.text = @"conversion not available";

    }

     [self.progressIndicator stopAnimating];

    

}