How do I get the NSDate plist representation programmatically?

Question

Since plist is xml, which is text, when an NSDate object is written into a plist, the result is something like this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
      <date>2011-04-01T02:09:15Z</date>
</plist>

I would like to obtain that string (011-04-01T02:09:15Z) directly, without all the surroundings. There has to be a more sensible way to do it than:

NSString *xmlRepresentationOfCurrentDate = [[[[[[[NSString alloc] initWithData:[NSPropertyListSerialization dataFromPropertyList:self format:kCFPropertyListXMLFormat_v1_0 options:0 error:NULL] encoding:NSUTF8StringEncoding] autorelease] componentsSeparatedByString:@"<date>"] objectAtIndex:1] componentsSeparatedByString:@"</date>"] objectAtIndex:0];

What complicates it is the fact that the representation above is GMT, and apparently the timezone is set during the creation of the NSDate object. An alternative to the above code I see is to get the GMT offset, use it in the dateWithTimeInterval:sinceDate: method to get the GMT date, and then use the NSDateFormatter to write out the above string. However, since that has even more overhead.

Is there any way to get just that xml string?

ughoavgfhw · Answer 1 · 2011-04-01T02:59:10.673

0

NSDate's description method returns a string using the format YYYY-MM-DD HH:MM:SS ±HHMM.

Edit: executor21 pointed out that the section below is only valid for OS X, not iOS.

If you don't want that format, you can use descriptionWithCalendarFormat:timeZone:locale: instead and define your own format. See http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSDate_Class/Reference/Reference.html%23//apple_ref/occ/instm/NSDate/description

edited Apr 01 '11 at 02:59

answered Apr 01 '11 at 02:34

ughoavgfhw

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`descriptionWithCalendarFormat:timeZone:locale:` is a Mac OS X method, it doesn't exist on the iOS. – executor21 Apr 01 '11 at 02:47
Sorry, I assumed Apple would have that available for both. I'll edit my post to show that. – ughoavgfhw Apr 01 '11 at 02:54
1

It's also “slated for deprecation”, so you shouldn't use it on either platform. – Peter Hosey Apr 01 '11 at 04:34

score 0 · Answer 2 · answered Apr 01 '11 at 02:50

0

If you're really creating property lists that contain just a single date, the code you posted seems like the right way to go. I can see how you might feel that's a little cumbersome, but you could always paste that into a method in a category on NSDate so that you can read or write dates directly from or to property list format.

answered Apr 01 '11 at 02:50

Caleb

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You're actually right, but the main problem is that `dataFromPropertyList:format:errorDescription:` is a method slated for deprecation and its replacement, `dataWithPropertyList:format:options:error:` is available only in iOS 4.0 and above. I need my code to run on the 3.1.3 and above systems. Under those circumstances, the NSDateFormatter is the best option (see my answer below). – executor21 Apr 05 '11 at 23:55
So why not test for the presence of `-dataWithPropertyList:format:options:error:`, and fall back to `-dataFromPropertyList:format:errorDescription:` if it's not available? – Caleb Apr 06 '11 at 00:59

score 0 · Accepted Answer · answered Apr 06 '11 at 00:01

It seems like the NSDateFormatter is actually the best option given the circumstances -- I need to run this on devices with iOS 3.1.3 and above, so dataWithPropertyList:format:options:error: method (introduced in 4.0) isn't an option, while dataFromPropertyList:format:errorDescription: is slated for deprecation.

Also, I made a mistake above: it should be

NSString *xmlRepresentationOfCurrentDate = [[[[[[[NSString alloc] initWithData:[NSPropertyListSerialization dataWithPropertyList:self format:kCFPropertyListXMLFormat_v1_0 options:0 error:NULL] encoding:NSUTF8StringEncoding] autorelease] componentsSeparatedByString:@"<date>"] objectAtIndex:1] componentsSeparatedByString:@"</date>"] objectAtIndex:0];

But the actual, all-versions solution is a category method on NSDate:

-(NSString *)xmlRepresentation{
    NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease];
    [formatter setTimeStyle:NSDateFormatterFullStyle];

    [formatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss"];
    [formatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"UTC"]];

    return [[formatter stringFromDate:self] stringByAppendingString:@"Z"];
}

How do I get the NSDate plist representation programmatically?

3 Answers3