Question

Possible Duplicates:
Comparing dates
How to compare two dates in Objective-C

i want to compare 2 strings who have a date format “11-06-2011” and “12-06-2011” for exemple.
i want to see if the second date is greater than the first or not
can you help me please ?

---

i tried this code

NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
    [dateFormat setDateFormat:@"dd-MM-YYYY"];
    NSDate *date1 = [dateFormat dateFromString:deparatureDateField.text];
    NSDate *date2 = [dateFormat dateFromString:comebackDateField.text];
    [dateFormat release];
    NSTimeInterval timeInterval = [date1 timeIntervalSinceDate:date2];
    if(timeInterval >= 0)
    {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Attention" message:@"come back date should be greater" delegate:self cancelButtonTitle:nil otherButtonTitles:@"Ok",nil];
        [alert show];
    }

but i alwayse have an alert, NSTimeInterval timeInterval is alwayse NULL

Answer 1

To find out if one date is larger than the other you’d have to do this:

NSString *string1 = @"11-06-2011";
NSString *string2 = @"12-06-2011";

// Convert string to date object
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:@"dd-MM-yyyy"];
NSDate *date1 = [dateFormat dateFromString:string1];
NSDate *date2 = [dateFormat dateFromString:string2];
[dateFormat release];

NSComparisonResult comparisonResult = [date1 compare:date2];

/*
NSComparisonResult can be either of these values:
 - NSOrderedAscending (-1) //if date1 < date2
 - NSOrderedSame (0)       //if date1 = date2
 - NSOrderedDescending (1) //if date1 > date2
*/

Alternatively (to compare:) you could use timeIntervalSinceDate: to get the actual time difference:

NSTimeInterval timeInterval = [date1 timeIntervalSinceDate:date2];
//timeInterval will be
// - nagative if ascending,
// - zero if same,
// - positive if descending