gistfile1.m

/*
 * This will convert DateTime (.NET) object serialized as JSON by WCF to a NSDate object.
 */

// Input string is something like: "/Date(1292851800000+0100)/", "\/Date(1292851800000-0100)\/" or "/Date(1292851800000)/" where
// 1292851800000 is milliseconds since 1970 and +0100 is the timezone
NSString *inputString = [item objectForKey:@"DateTimeSession"];

// This will tell number of seconds to add according to your default timezone
// Note: if you don't care about timezone changes, just delete/comment it out
NSInteger offset = [[NSTimeZone defaultTimeZone] secondsFromGMT];

// The start of the date value (can't assume position, because the / might be escaped)
NSInteger startPosition = [strValue rangeOfString:@"("].location + 1;
             
NSTimeInterval unixTime = [[strValue substringWithRange:NSMakeRange(startPosition, 13)] doubleValue] / 1000;
      
NSDate *date = [[NSDate dateWithTimeIntervalSince1970:unixTime]
                        dateByAddingTimeInterval:offset];       
// You can just stop here if all you care is a NSDate object from inputString,
// or see below on how to get a nice string representation from that date:

// static is nice if you will use same formatter again and again (for example in table cells)
static NSDateFormatter *dateFormatter = nil;
if (dateFormatter == nil) {
    dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateStyle:NSDateFormatterShortStyle];
    [dateFormatter setTimeStyle:NSDateFormatterNoStyle];

    // If you're okay with the default NSDateFormatterShortStyle then comment out two lines below
    // or if you want four digit year, then this will do it:
    NSString *fourDigitYearFormat = [[dateFormatter dateFormat]
                                     stringByReplacingOccurrencesOfString:@"yy"
                                     withString:@"yyyy"];
    [dateFormatter setDateFormat:fourDigitYearFormat];
}

// There you have it:
NSString *outputString = [dateFormatter stringFromDate:date];