Parsing JSON dates on IPhone

Question

Forgive me as I'm new to Objective C.

I am getting back dates from a .NET webservice in the /Date(xxxxxxxxxxxxx-xxxx)/ format. I'm looking for some direction on how to best parse this into an NSDate object. I've tried using dateWithTimeIntervalSince1970 on it but it comes back with a date in the year 1969 for a date I know is in 2006.

Looking for some direction on the proper way to handle JSON dates.

Thanks in advance!

Answer 1

I just wrote this for iOS 4.0+ (because it uses NSRegularExpression). It handles dates with or without timezone offsets. Seems to work pretty well, what do you think?

+ (NSDate *)mfDateFromDotNetJSONString:(NSString *)string {
    static NSRegularExpression *dateRegEx = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        dateRegEx = [[NSRegularExpression alloc] initWithPattern:@"^\\/date\\((-?\\d++)(?:([+-])(\\d{2})(\\d{2}))?\\)\\/$" options:NSRegularExpressionCaseInsensitive error:nil];
    });
    NSTextCheckingResult *regexResult = [dateRegEx firstMatchInString:string options:0 range:NSMakeRange(0, [string length])];

    if (regexResult) {
        // milliseconds
        NSTimeInterval seconds = [[string substringWithRange:[regexResult rangeAtIndex:1]] doubleValue] / 1000.0;
        // timezone offset
        if ([regexResult rangeAtIndex:2].location != NSNotFound) {
            NSString *sign = [string substringWithRange:[regexResult rangeAtIndex:2]];
            // hours
            seconds += [[NSString stringWithFormat:@"%@%@", sign, [string substringWithRange:[regexResult rangeAtIndex:3]]] doubleValue] * 60.0 * 60.0;
            // minutes
            seconds += [[NSString stringWithFormat:@"%@%@", sign, [string substringWithRange:[regexResult rangeAtIndex:4]]] doubleValue] * 60.0;
        }

        return [NSDate dateWithTimeIntervalSince1970:seconds];
    }
    return nil;
}

Answer 2

I was in the same boat whilst using json-framework which doesn't support the date format as it's not official JSON. My source is from an API built using JSON.Net. This is what I came up with:

- (NSDate*) getDateFromJSON:(NSString *)dateString
{
    // Expect date in this format "/Date(1268123281843)/"
    int startPos = [dateString rangeOfString:@"("].location+1;
    int endPos = [dateString rangeOfString:@")"].location;
    NSRange range = NSMakeRange(startPos,endPos-startPos);
    unsigned long long milliseconds = [[dateString substringWithRange:range] longLongValue];
    NSLog(@"%llu",milliseconds);
    NSTimeInterval interval = milliseconds/1000;
    return [NSDate dateWithTimeIntervalSince1970:interval];
}

I don't have the appended portion in the date format that you do so I haven't dealt with that like the answer above. No error catching either, it's all new to me at this point.

Answer 3

I actually found the snippet with NSRegularExpression pretty useful, till i came up with another solution that uses NSCharecterSet for stipping off the milliseconds.

+ (NSDate*) dateFromJSONString:(NSString *)dateString
{
    NSCharacterSet *charactersToRemove = [[ NSCharacterSet decimalDigitCharacterSet ] invertedSet ];
    NSString* milliseconds = [dateString stringByTrimmingCharactersInSet:charactersToRemove];   

    if (milliseconds != nil && ![milliseconds isEqualToString:@"62135596800000"]) {
        NSTimeInterval  seconds = [milliseconds doubleValue] / 1000;
        return [NSDate dateWithTimeIntervalSince1970:seconds];
    }
    return nil;
}

Saves a lot of the manual string processing and makes the code much cleaner.

Answer 4

As a .NET programmer learning Objective-C I had the same problem when I tried to consume a .Net WebService.

At first I thought I would be able to use the NSDateFormatter... I found a really good reference for it's symbols here, but I quickly realized that I needed to convert the number from milliseconds to seconds.

I wrote the code to do it... I'm still learning Obj-C but I dont think It should've been this hard...

- (NSDate *) getJSONDate{
    NSString* header = @"/Date(";
    uint headerLength = [header length];

    NSString*  timestampString;

    NSScanner* scanner = [[NSScanner alloc] initWithString:self];
    [scanner setScanLocation:headerLength];
    [scanner scanUpToString:@")" intoString:&timestampString];

    NSCharacterSet* timezoneDelimiter = [NSCharacterSet characterSetWithCharactersInString:@"+-"];
    NSRange rangeOfTimezoneSymbol = [timestampString rangeOfCharacterFromSet:timezoneDelimiter];

    [scanner dealloc];

    if (rangeOfTimezoneSymbol.length!=0) {
        scanner = [[NSScanner alloc] initWithString:timestampString];

        NSRange rangeOfFirstNumber;
        rangeOfFirstNumber.location = 0;
        rangeOfFirstNumber.length = rangeOfTimezoneSymbol.location;

        NSRange rangeOfSecondNumber;
        rangeOfSecondNumber.location = rangeOfTimezoneSymbol.location + 1;
        rangeOfSecondNumber.length = [timestampString length] - rangeOfSecondNumber.location;

        NSString* firstNumberString = [timestampString substringWithRange:rangeOfFirstNumber];
        NSString* secondNumberString = [timestampString substringWithRange:rangeOfSecondNumber];

        unsigned long long firstNumber = [firstNumberString longLongValue];
        uint secondNumber = [secondNumberString intValue];

         NSTimeInterval interval = firstNumber/1000;

        return [NSDate dateWithTimeIntervalSince1970:interval];
    }

    unsigned long long firstNumber = [timestampString longLongValue];
    NSTimeInterval interval = firstNumber/1000;

    return [NSDate dateWithTimeIntervalSince1970:interval];
}

Hopefully someone can provide a better Obj-C solution. If not I may keep this or look for a way to change the serialization format in .NET

EDIT:

About that JSON DateTime format... If you have any control on the service it would probably be best to convert the date to a string in your DataContract objects.

Formatting to RFC1123 seems like a good idea to me right now. As I can probably pick it up easily using a NSDateFormatter.

Quote from Rick Strahl

There's no JavaScript date literal and Microsoft engineered a custom date format that is essentially a marked up string. The format is a string that's encoded and contains the standard new Date(milliseconds since 1970) value.

Answer 5

Theory: MS encoded the C# DateTime in JSON as milliseconds since 1970. Solution:

NSString*
    dateAsString = @"/Date(1353720343336+0000)/";
    dateAsString = [dateAsString stringByReplacingOccurrencesOfString:@"/Date("
                                                           withString:@""];
    dateAsString = [dateAsString stringByReplacingOccurrencesOfString:@"+0000)/"
                                                           withString:@""];

unsigned long long milliseconds = [dateAsString longLongValue];
NSTimeInterval interval = milliseconds/1000;
NSDate* date = [NSDate dateWithTimeIntervalSince1970:interval];

This is the shortest solution I can think of.

Answer 6

Use an NSDateFormatter's dateFromString: method after setting the date format.

Answer 7

-(NSString*)convertToUTCTime:(NSString*)strDate{

NSDate *currentDate = [NSDate date];
myDate = [commonDateFormatter dateFromString: strDate];
NSTimeInterval distanceBetweenDates = [currentDate timeIntervalSinceDate:myDate];
return [self stringFromTimeInterval:distanceBetweenDates];

} - (NSString *)stringFromTimeInterval:(NSTimeInterval)interval { NSInteger ti = (NSInteger)interval; NSInteger minutes = (ti / 60) % 60; NSInteger hours = (ti / 3600);

if (hours > 24) {
    NSInteger days = hours/24;
    if (days > 30) {
       NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
       [dateFormatter setDateFormat:@"EEE d MMM, h:mm a"];
       //[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"IST"]];
        NSString *daydate = [dateFormatter stringFromDate:myDate];
        return daydate;
    }
    else{
    return [NSString stringWithFormat:@" %2ldd",(long)days];
    }
}else{
    if (hours == 0 && minutes < 1) {
        return [NSString stringWithFormat:@"Today"];
    }
    else if (hours == 0 && minutes < 60){
        return [NSString stringWithFormat:@"%2ldm ",(long)minutes];
    }
    else{
    return [NSString stringWithFormat:@" %2ldh",(long)hours];
    }
}

}