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iosobjective-cnsdateformatternsexpression

stringFromDate not converting an NSDate to string

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

Solution

  • 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.