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I have an NSTableView that is bound to an NSArrayController (that in turn gets the data from an NSMutableArray), how can I format an NSDate object that is within that array? Right now Its giving me “2004-11-24 14:00:00 -0500” if i initialize the NSDate with a language string.. and “Wednesday, November 24, 2004 2:00:00” if i use [NSDate date] to initialize it. I would like it to use a relative date, like… ie. “Yesterday” or otherwise “2004-11-24” or something simple like that (ie. a short string instead of the huge one it is giving me by default).

I am aware that I can subclass NSDate or add a value transformer. But I am wondering what the best/recommended approach is?

I’d use an NSValueTransformer/NSDateFormatter and do the following.

Theres an example here which I’ve added below.

-(NSString *)stringForObjectValue:(id)obj { � �if(![obj isKindOfClass: [NSDate class]]) � � � �return nil; � � � �NSCalendarDate *inDate=obj; � �if(![obj isKindOfClass: [NSCalendarDate class]])//if not calendarDate, then convert � � � �inDate=[obj dateWithCalendarFormat:nil timeZone:nil]; � � � �NSUserDefaults *theDefault=[NSUserDefaults standardUserDefaults]; � �int today=[[NSCalendarDate calendarDate]dayOfCommonEra]; � �int dateDay=[inDate dayOfCommonEra]; � � � � � � � � � �if(dateDay==today) � � � �return [theDefault stringArrayForKey:@”[[NSThisDayDesignations”] objectAtIndex:0]; � � � � � �if(dateDay==(today+1)) � � � �return [theDefault stringArrayForKey:@”[[NSNextDayDesignations”] objectAtIndex:0] capitalizedString]; � � � � � �if(dateDay==(today-1)) � � � �return [theDefault stringArrayForKey:@”[[NSPriorDayDesignations”] objectAtIndex:0] capitalizedString]; � � � �return [super stringForObjectValue:obj]; � � }

If you don’t mind not having the Today, Tomorrow, Yesterday designations you can just use dateWithNaturalLanguageString, and %Y-%m-%d as your formatter string.

I’m trying to learn how to build my app with CoreData and Bindings (decided I’d had enough of the glue code) - and I think I’ve got myself in a pickle.

Quite simply I have a class in my data model with an NSDate/NSCalendarDate (model just says ‘date’) attribute in it.

I’d like to show this attribute in a TableView via bindings. But ah - NSTableViews don’t know how to write a ‘Date’ in a text cell, so I looked up and wrote a Date->String NSValueTransformer subclass, and now my dates display fine.

However, I think I am correct in understanding that NSValueTransformer subclasses are only allowed to convert to the same class of object both ways… so because I am putting in a Date a String is popping out at the moment, if I implement the reverse method then it would still expect a String to be returned? Which will not fit with my data model obviously!

It seems that I can do what I wanted (perhaps the Apple docs on NSValueTransformer are a little misleading here?).

There is still a problem with bringing dates out into a string, and then popping them back into the data model when they are changed in a tableview.

The documentation says to be aware of losing precision thorough an NSValueTransformer, yet that’s exactly the position I find myself facing:

My model stores a Date. This date stores an important time down to the second (i.e. I’m interested in the year, month, day, hour, min, and sec information). I want my tableview in this instance just to display the year/month/day information. I want the user to be able to edit this info without changing the hour/min/sec information in that date. However doing things via the Transformer, the user comes along, sets a new date to ‘10/10/2005’ and my transformer changes that attribute to be an NSDate with that year month and day, but with 12:00:00 for hour min second - i.e. not keeping my original hour min sec!

I think I will need access to the original date from the NSValueTransformer before changing it… but not sure how to do this :-S

Use NSDateFormatter

NSDateFormatter seems to do away with my need to use a ValueTransformer, which is great.

However, I still have the precision problem, if my MODEL must store a date complete with important hour/min/sec information, but I only need a particular VIEW to display and allow changes to the year/month/day information, when the user changes the date in that view, the time (hour/min/sec) is reset to 00:00:00 - this behaviour is not desired.

This is not a problem with Cocoa but of your view not meeting its requirements/obligations to the model. The view editor must at least allow time down to seconds to be entered, if not also displayed. A quick look at the NSDateFormatter shows a Long and Full style format string that includes hh:mm:ss but this is only available in 10.4.

I will not allow the user to change the date in the tableview, but will instead provide a button-cell that pops up a custom UI complete with all time information so that will suit the model requirements properly.