how to extract date components from sum of year month day weekday multiply by certain integer in iOS?

Question

The apple sample project DateSectionTitles demonstrates how to group sections by year and month, how to extends it to support year month day and weekday?

sectionIdentifier is a transient attribute derives from persistent date attribute timestamp.

- (NSString *)sectionIdentifier {

    // Create and cache the section identifier on demand.

    [self willAccessValueForKey:@"sectionIdentifier"];
    NSString *tmp = [self primitiveSectionIdentifier];
    [self didAccessValueForKey:@"sectionIdentifier"];

    if (!tmp) {
        /*
         Sections are organized by month and year. Create the section identifier
         as a string representing the number (year * 1000 + month);
         this way they will be correctly ordered chronologically regardless of
         the actual name of the month.
         */
        NSCalendar *calendar = [NSCalendar currentCalendar];

        NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit)
                               fromDate:[self timeStamp]];
        tmp = [NSString stringWithFormat:@"%d", [components year] * 1000 + [components month]];
        [self setPrimitiveSectionIdentifier:tmp];
    }
    return tmp;
}

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
    id <NSFetchedResultsSectionInfo> theSection = [[self.fetchedResultsController sections] objectAtIndex:section];

    /*
     Section information derives from an event's sectionIdentifier, which is a string representing the number (year * 1000) + month.
     To display the section title, convert the year and month components to a string representation.
     */
    static NSDateFormatter *formatter = nil;

    if (!formatter)
    {
        formatter = [[NSDateFormatter alloc] init];
        [formatter setCalendar:[NSCalendar currentCalendar]];

        NSString *formatTemplate = [NSDateFormatter dateFormatFromTemplate:@"MMMM YYYY" options:0 locale:[NSLocale currentLocale]];
        [formatter setDateFormat:formatTemplate];
    }

    NSInteger numericSection = [[theSection name] integerValue];
    NSInteger year = numericSection / 1000;
    NSInteger month = numericSection - (year * 1000);

    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.year = year;
    dateComponents.month = month;
    NSDate *date = [[NSCalendar currentCalendar] dateFromComponents:dateComponents];

    NSString *titleString = [formatter stringFromDate:date];

    return titleString;
}

I don't know the exact algorithm to calculate year month day and weekday like below code.

tmp = [NSString stringWithFormat:@"%d", [components year] * 1000 + [components month]];

And the calculate for the data source method.

id <NSFetchedResultsSectionInfo> theSection = [[self.fetchedResultsController sections] objectAtIndex:section];

NSInteger numericSection = [[theSection name] integerValue];
NSInteger year = numericSection / 1000;
NSInteger month = numericSection - (year * 1000);

score 1 · Accepted Answer · answered Mar 13 '15 at 15:52

You need an "algorithm" that creates a different result for each day (weekday is the same as day. There is no "Thursday, 13 March 2015").

Let's say you have the 13th of March 2015. A good unique string for this would be 20150313. Or year * 10000 + month * 100 + day.

e.g.:

NSDateComponents *components = [calendar components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay)
                                               fromDate:[self timeStamp]];
tmp = [NSString stringWithFormat:@"%d", [components year] * 10000 + [components month] * 100 + [components day]];

Then invert the calculations to get back the individual components:

NSInteger numericSection = [[theSection name] integerValue];
NSInteger year = numericSection / 10000;
NSInteger month = (numericSection - (year * 10000))/100;
NSInteger day = (numericSection - (year * 10000 + month * 100))

Or just get the NSDate from one of the objects in the section:

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
    id <NSFetchedResultsSectionInfo> theSection;// = [[self.fetchedResultsController sections] objectAtIndex:section];
    static NSDateFormatter *formatter = nil;

    if (!formatter)
    {
        formatter = [[NSDateFormatter alloc] init];
        [formatter setCalendar:[NSCalendar currentCalendar]];

        NSString *formatTemplate = [NSDateFormatter dateFormatFromTemplate:@"MMMM yyyy dd EEEE" options:0 locale:[NSLocale currentLocale]];
        [formatter setDateFormat:formatTemplate];
    }

    APLEvent *event = [[theSection objects] firstObject];
    if (event) {
        NSDate *date = [event timeStamp];
        return [formatter stringFromDate:date];
    }
    return nil;
}

how to extract date components from sum of year month day weekday multiply by certain integer in iOS?

1 Answers1