NSCalendar components fromDate toDate options example in Objective C (iOS).

NSCalendar components fromDate toDate options

Returns, as an NSDateComponents object using specified components, the difference between two supplied dates.

- (NSDateComponents *)components:(NSUInteger)unitFlags fromDate:(NSDate *)startingDate toDate:(NSDate *)resultDate options:(NSUInteger)opts

Parameters of [NSCalendar components fromDate toDate options]
unitFlags
Specifies the components for the returned NSDateComponents object—a bitwise OR of NSCalendarUnit constants.
startingDate
The start date for the calculation.
resultDate
The end date for the calculation.
opts
Options for the calculation.
If you specify a “wrap” option (NSWrapCalendarComponents), the specified components are incremented and wrap around to zero/one on overflow, but do not cause higher units to be incremented. When the wrap option is false, overflow in a unit carries into the higher units, as in typical addition.

Return Value of [NSCalendar components fromDate toDate options]
An NSDateComponents object whose components are specified by unitFlags and calculated from the difference between the resultDate and startDate using the options specified by opts. Returns nil if either date falls outside the defined range of the receiver or if the computation cannot be performed.

Discussion of [NSCalendar components fromDate toDate options]
The result is lossy if there is not a small enough unit requested to hold the full precision of the difference. Some operations can be ambiguous, and the behavior of the computation is calendar-specific, but generally larger components will be computed before smaller components; for example, in the Gregorian calendar a result might be 1 month and 5 days instead of, for example, 0 months and 35 days. The resulting component values may be negative if resultDate is before startDate.

The following example shows how to get the approximate number of months and days between two dates using an existing calendar (gregorian):
NSCalendar components fromDate toDate options example.

NSDate *startDate = ...;
NSDate *endDate = ...;
unsigned int unitFlags = NSMonthCalendarUnit | NSDayCalendarUnit;
NSDateComponents *comps = [gregorian components:unitFlags fromDate:startDate  toDate:endDate  options:0];
int months = [comps month];
int days = [comps day];

Example of [NSCalendar components fromDate toDate options].

- (int) daysToDate:(NSDate*) endDate
{
    //dates needed to be reset to represent only yyyy-mm-dd to get correct number of days between two days.
    NSDateFormatter *temp = [[NSDateFormatter alloc] init];
    [temp setDateFormat:@"yyyy-MM-dd"];
    NSDate *stDt = [temp dateFromString:[temp stringFromDate:self]];
    NSDate *endDt =  [temp dateFromString:[temp stringFromDate:endDate]];
    [temp release];
    unsigned int unitFlags = NSMonthCalendarUnit | NSDayCalendarUnit;
    NSCalendar *gregorian = [[NSCalendar alloc]
                             initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *comps = [gregorian components:unitFlags fromDate:stDt  toDate:endDt  options:0];
    int days = [comps day];
    [gregorian release];
    return days;
}

NSCalendar components fromDate toDate options example.

-(NSInteger)daysBetweenTwoDates:(NSDate*)fromDateTime andDate:(NSDate*)toDateTime
{

NSDate *fromDate;
NSDate *toDate;

NSCalendar *calendar = [NSCalendar currentCalendar];

[calendar rangeOfUnit:NSDayCalendarUnit startDate:&fromDate
             interval:NULL forDate:fromDateTime];
[calendar rangeOfUnit:NSDayCalendarUnit startDate:&toDate
             interval:NULL forDate:toDateTime];

NSDateComponents *difference = [calendar components:NSDayCalendarUnit
                                           fromDate:fromDate toDate:toDate options:0];

return [difference day];
}

End of NSCalendar components fromDate toDate options example article.