stringFromDate not converting an NSDate to string

Question

I have some simple code which should convert an NSDate which I retrieve from CoreData. For some reason it is not working in this class when the same code works in other views. What am I doing wrong? Below is the offending code and a screen shot of my log...

NSFetchRequest *request26 = [[NSFetchRequest alloc] init];
[request26 setEntity:entityDiscription];
[request26 setResultType:NSDictionaryResultType];
NSExpression *keyPathExpression26 = [NSExpression expressionForKeyPath:@"date"];
NSExpression *swimLast750Expression = [NSExpression expressionForFunction:@"max:" arguments:[NSArray arrayWithObject:keyPathExpression26]];
NSExpressionDescription *expressionDescription26 = [[NSExpressionDescription alloc] init];
[expressionDescription26 setName:@"swimLast750"];
[expressionDescription26 setExpression:swimLast750Expression];
[expressionDescription26 setExpressionResultType:NSInteger16AttributeType];
[request26 setPropertiesToFetch:[NSArray arrayWithObject:expressionDescription26]];
NSPredicate *pred26 = [NSPredicate predicateWithFormat:@"(date >= %@) AND (sport like %@) AND (sessiontype like %@)", swimSinceDateAsDate, sportTypeSwim, sessType1];
[request26 setPredicate:pred26];

NSError *error26;
NSArray *objects26 = [context executeFetchRequest:request26 error:&error26];
if (objects26 == nil) {
    NSLog(@"The fetch request returned an array == nil");
} else {
    NSLog(@"Contents of Array Object26 is:%@", objects26);
    NSDate *sessDate = [[objects26 objectAtIndex:0] valueForKey:@"swimLast750"];
    NSLog(@"NSDate is: %@", sessDate);
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"dd-MMM-yyyy"];
    NSLog(@"DATE FORMATTER: %@", [formatter stringFromDate:[[objects26 objectAtIndex:0] valueForKey:@"swimLast750"]]);
    NSString *dateString = [formatter stringFromDate:sessDate];
    //NSString *dateString = [formatter stringFromDate:[[objects26 objectAtIndex:0] valueForKey:@"swimLast750"]];
    NSLog(@"dateString is: %@", dateString);
    sw750Last = dateString;
}

NSLog Output

`sessDate` is not an `NSDate`. Looks like it's maybe a timestamp -- a number of seconds offset from some reference time; could be stored as either an `NSNumber` or `NSString`. — jscs, Oct 25 '13 at 05:52

score 4 · Accepted Answer · answered Oct 25 '13 at 06:53

You have set

[expressionDescription26 setExpressionResultType:NSInteger16AttributeType];

which causes the fetch request to return the date as an NSNumber. This number is the number of seconds since the "reference date" 1 January 2001, GMT), so you could convert that to NSDate with

NSNumber *sessDateAsNumber = [[objects26 objectAtIndex:0] valueForKey:@"swimLast750"];
NSDate *sessDate = [NSDate dateWithTimeIntervalSinceReferenceDate:[sessDateAsNumber doubleValue]];

But the better solution is probably to use

[expressionDescription26 setExpressionResultType:NSDateAttributeType];

in the expression description. Then the date is returned as NSDate object, and stringFromDate works as expected.

you absolutely nailed it. I looked at that code so many times and didn't even clock the attributeType - so annoyed with myself. Thank you for the response all working perfectly now that I've changed it to NSDateAttributeType! Genius! — Sean, Oct 25 '13 at 16:45

vignesh kumar · Answer 2 · 2013-10-25T06:46:29.277

1

You have to convert the timestamps into date using the below code.I think you will get it as NSNumber so you have to convert it into a double value before

NSTimeInterval interval = [sessDate doubleValue];
NSDate *swimLast750=[NSDate dateWithTimeIntervalSince1970:interval];

edited Oct 25 '13 at 06:46

answered Oct 25 '13 at 05:54

vignesh kumar

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This assumes that the timestamp is relative to the Unix epoch. – jscs Oct 25 '13 at 05:55
This actually does not work. The date is stored as an NSDate but I was retrieving it from coredata as an number so when I converted from an interval since 1970 as you suggested I got a date of 05-Oct-1984 instead of 05-Oct-2013... But thanks for the suggestion... – Sean Oct 25 '13 at 16:53

score 0 · Answer 3 · answered Oct 25 '13 at 09:11

First thing you need to change the time interval to date and then set the specified format. Try below code:-

NSDate *date=[NSDate dateWithTimeIntervalSinceReferenceDate:402663864];
NSDateFormatter *formatter=[[NSDateFormatter alloc]init];
[formatter setDateFormat:@"yyyy-MM-dd"];
NSLog(@"%@",date);
NSString *dateString=[formatter stringFromDate:date];
NSLog(@"dateString=%@",dateString);

stringFromDate not converting an NSDate to string

3 Answers3