Recently I’ve been working on an iOS project that loads data that we publish via the Open Data Protocol (OData).
At first everything was working perfectly. I was using JSONKit and NSOperation to download and process the information. That was until I had to get a DateTime object…which resulted in an epic fail!
It turns out that WCF Data Services publish DateTime objects as a new Date object represented by the time in milliseconds (not seconds) since January 1, 1970. Anyone familiar with EPOCH dates knows about January 1, 1970 right?
The problem isn’t so much in that it publishes dates from a known time, rather that it does it in the least accessible way! The value is rendered out (in JSON) as “\/Date(1311836400000)\/” – yeah..I know, right?
So now I had to figure out a nice way to parse this very custom date format in Objective-C. This led me to the shocking (and borderline unacceptable) realization that objective-c (lower case to drive the point home) has no support for regular expressions. There’s no punch-line to this joke…for real. No support for regex. A Unix-based OS has a development language that has no support for something that is natively supported (see the * below)!
To start, I decided to add a category to the NSDate object that would allow me to work with these ridiculous strings.
NSDate+OData.h
#import <Foundation/Foundation.h> @interface NSDate (OData) - (id)initWithODataString:(NSString *)dateString; - (NSString *)toODataQueryFormat; + (NSDate *)dateFromString:(NSString *)dateString; @end
NSDate+OData.m
#import "NSDate+OData.h"
@implementation NSDate (OData)
- (id)initWithODataString:(NSString *)dateString
{
return [[NSDate dateFromString:dateString] retain];
}
- (NSString *)toODataQueryFormat
{
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss"];
NSString *formattedDate = [formatter stringFromDate:self];
[formatter release];
return formattedDate;
}
+ (NSDate *)dateFromString:(NSString *)dateString
{
NSInteger startIndex = [dateString rangeOfString:@"("].location;
NSInteger endIndex = [dateString rangeOfString:@")"].location - startIndex;
long long ticks = [[dateString substringWithRange:NSMakeRange(startIndex + 1, endIndex)] longLongValue];
NSDate *date = [NSDate dateWithTimeIntervalSince1970:(ticks / 1000)];
return date;
}
@end
The code above allows me to get an NSDate from the crazy OData DateTime string and also convert an NSDate to another (quite different) format used by OData to query based on a DateTime value.
To get an NSDate from the OData string, I am substring’ing the value between the two brackets. This value is then converted to a long long value (twice on purpose for you .NET developers out there). The NSDate has a static method called dateWithTimeIntervalSince1970: that will return an (autoreleased) NSDate object with the value of the time (in seconds) since January 1, 1970.
To get the date to the query format used by OData (see OData URI Conventions), we need to take an NSDate and get it into the format “yyyy-MM-dd’T'HH:mm:ss” for example, “2011-07-29T18:15:00″.
I hope this information helps someone, as I was unable to find a simple example online anywhere (although I will concede that my googling skills could use some work).
* Please don’t take this as a complete knock to Objective-C. The language is quite easy to work with and definitely robust…just lame on the regex front!
