SORelativeDateTransformer is a value transformer that generates a human-readable phrase expressing the relative difference between a given date and the current date.

For example, when the current date-time is 2010-12-05 11:30, then

... 2010-12-05 11:00 is transformed to "30 minutes ago"

... 2010-12-01 11:00 is transformed to "5 days ago"

... 2010-12-25 08:00 is transformed to "in 2 weeks"

The transformer does not provide reverse transformations; you can only transform from an NSDate to an NSString.

Add the source files and localized strings bundle to your project.

SORelativeDateTransformer.h
SORelativeDateTransformer.m
SORelativeDataTransformer.bundle

Create an instance of SORelativeDateTransformer wherever you need to generate relative date phrases.

// Display a file's creation date relative to today's date
NSURL *someFilePath = ...;
NSDictionary *attribs = [[NSFileManager defaultManager] attributesOfItemAtPath:someFilePath error:NULL];

NSDate *dateModified = [attribs fileModificationDate];

// fileModificationDate is 2010-10-01 12:00:00TZ; 
// Date now is 2010-10-30 12:00:00TZ

SORelativeDateTransformer *relativeDateTransformer = [[SORelativeDateTransformer alloc] init];
NSString *relativeDate = [relativeDateTransformer transformedValue: dateModified];

NSLog (@"This file was modified %@.", relativeDate); // ==> "This file was modified 3 weeks ago."

The accompanying bundle, SORelativeDateTransformer.bundle, provides localizations for the date component names and their plural forms.

Included localizations:

• English
• Japanese
• French
• German
• Spanish
• Dutch
• Simplified Chinese
• Traditional Chinese

The localization also includes NSString-compatible format templates for phrases expressing relative past and future dates.

• For past dates, the format template for the English phrase is "%d %@ ago". E.g. 20 minutes ago
• For future dates, the format template is "in %d %@". E.g. in 20 minutes

To add your own localizations, copy the English localization within SORelativeDateTransformer.bundle directory to an appropriately named .lproj subdirectory, then edit the .strings file within that new localization subdirectory.

For example, to add an Italian localization:

# Change working directory to the SORelativeDateTransformer.bundle

cd ${PROJECT_DIR}/SORelativeDateTransformer.bundle

# Copy the English localization subdirectory
# to an appropriately named lproj directory for an Italian localization

cp -R en.lproj it.lproj

# Edit the .strings file within the Italian lproj directory
# to replace the English localization values with Italian equivalents.
# Use your favorite UTF-16-capable text editor.

mate it.lproj/SORelativeDateTransformer.strings

Included is an iOS 4 interactive testing application. You can a date from the date picker and see the generated relative date string below.

SORelativeDateTransformer is compatible with iOS 4 and later, and Mac OS X 10.4 and later. Supports use in ARC and non-ARC projects.

Use it, hack it, but give me some love.

Creative Commons Attribution-ShareAlike 3.0 Unported License.

For a non-attribution license, contact http://standardorbit.net.

Bill Garrison, for the initial implementation. @github, @bitbucket

Ching-Lan 'digdog' Huang, for his NSDate category NSDate-RelativeDate upon which I based the value transformer. @github.

Adam Ernst, for reorganizing into a cleaner layout for easier project integration. @github.

Markus Gasser, for correcting the German localization. @github.

Martin Destagnol, for correcting the French localization and pushing for ARC compatibility. @github.

Hendrik Bruinsma, for contributing the Dutch localization. @github.

Vince Yuan, for contributing the Simplified & Traditional Chinese localizations. @github.

Brian Gesiak, for contributing the Japanese localization. @github.