How to fetch json data using url and write it in file?

Question

As my above screen shot that i have a json file (productDetail.json) in my app then i write file from json data like below code

else if([(MultipleURLConnection *)connection tag]==2)
    {
  if([fn writeToFile:responseData fileName:@"productDetail.json"])
       [self performSelector:@selector(loadingJSON) withObject:nil afterDelay:0.1];
    }

in above code responseData is NSMutableData and fn is function Class object name where i have below method

- (BOOL)writeToFile:(NSData *)data fileName:(NSString *)fileName 
 {
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *myFile = [documentsDirectory stringByAppendingPathComponent:fileName];
NSFileManager *fm = [NSFileManager defaultManager];
if (![fm fileExistsAtPath:myFile])  // if file doesn't exist, create it
    return ([fm createFileAtPath:myFile contents:data attributes:nil]);
else
    return ([data writeToFile:myFile atomically:YES]);  
 }

Now i decide to remove json file from app and to put it on server and then fetch it .so after putting json file on server i tried to fetch it like below coding

else if([(MultipleURLConnection *)connection tag]==2)
    {
        NSURL *url = [NSURL URLWithString:@"http://mysite.com/Infomist/productDetail.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(@"show data %@",result);
       }

Now above method successfully fetching my data from server it show all my data in NSlog but problem for me is now how to modify this Method now

     if([fn writeToFile:responseData fileName:@"])

Beacuse after putting the json file on server i don't have any file to pass file name in above method to call the

- (BOOL)writeToFile:(NSData *)data fileName:(NSString *)fileName  .

I already have App flow for local json file so i need only to write json data in my app.

Answer 1

- (BOOL)writeToFile:(NSData *)data fileName:(NSString *)fileName 

the above requires NSData as a parameter

        id result = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:&error];

the above gives id as a return type object..you need to check which type of object it is using isKindOfClass

and then later convert it to data using decoding/NSkeyedArchiver or other techniques