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

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)/" 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];

// A range of NSMakeRange(6, 10) will generate "1292851800" from "/Date(1292851800000+0100)/"
// as in example above. We crop additional three zeros, because "dateWithTimeIntervalSince1970:"
// wants seconds, not milliseconds; since 1 second is equal to 1000 milliseconds, this will work.
// Note: if you don't care about timezone changes, just chop out "dateByAddingTimeInterval:offset" part
NSDate *date = [[NSDate dateWithTimeIntervalSince1970:
                 [[inputString substringWithRange:NSMakeRange(6, 10)] intValue]]
                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];

If the date is pre 2001 it will be less than 10 characters, and you will accidentally consume one of the trailing 0's. I appreciate you want to keep it lean and not parse the whole string to find the end of the text, see my fork for my modification where I look for the start of the number, and use doubleValue which reads the string up to the ), + or - character and divide by 1000 to get time in seconds.

In my project I removed the timezone stuff and format for locales in the UI, but that's up to you

@tristandl since I don't have time to try this I'll take your word about pre 2001 less than 10 chars issue and I'll agree with you. I knew a range of (6, 10) was just an ugly hack to do this, but I assumed JSON string was always "that much long"... Soonish I will create a repo for this and put some other little things of mine for Objective-C language, so I will get serious&deeper on this. Your fix, one way or another, will definitely be there. Thank a lot!

Check out also RestKit/RestKit#264

@exalted Thank you very much, it really helped me !

@Ded77 you're welcome... ;-)