Invalidating section identifier

Question

I am using a transient attribute to sort the core data objects into separate table view sections. It is called 'sectionIdentifier'. The getter for this attribute is inside a NSManagedObject subclass, called ToDoItem.m . The problem is that during app execution, the new added objects are always shown under the TODAY section. After a new launch of the app, all objects are shown under the expected row. I was told by an expert user, that when setting a new object, the sectionIdentifier must be invalidated, but I don't know how to invalidate it. Here is my NSManagedObject subclass code:

#import "ToDoItem.h"
#import "ToDoGroup.h"
#import "ToDoSubItem.h"


@implementation ToDoItem

@dynamic todoDescription;
@dynamic todoName;
@dynamic todoDueDate;
@dynamic sectionIdentifier;
@dynamic todogroup;
@dynamic todosubitems;



-(NSString *)sectionIdentifier{

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

    if (!tmp){

        NSDate *date = self.todoDueDate;
        NSDate *todayDate = [NSDate date];

        NSLog(@"date= %@",date);
        NSLog(@"todayDate = %@",todayDate);


        NSCalendar *calendar = [NSCalendar currentCalendar];
        NSInteger comps = (NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit);
        NSDateComponents *date1Components = [calendar components:comps fromDate:date];
        NSDateComponents *date2Components = [calendar components:comps fromDate:todayDate];
        date = [calendar dateFromComponents:date1Components];
        todayDate = [calendar dateFromComponents:date2Components];




        if([date
            compare:todayDate] == NSOrderedSame) {
            tmp = @"1";//TODAY
        }
        else if([date
                 compare:todayDate] == NSOrderedDescending){
            tmp = @"2";//OVERDUE
        }
        else if ([date
                  compare:todayDate] == NSOrderedAscending){
            tmp =@"0";//UPCOMING
        }
        NSLog(@"Tmp= %@",tmp);

        [self setPrimitiveValue:tmp forKey:@"sectionIdentifier"];

    }
    return tmp;

}


@end

Any help is welcome...

Answer 1

The problem is that the section identifier is calculated and cached from the todoDueDate, but not updated automatically when the todoDueDate changes.

The DateSectionTitles/APLEvent.m sample code from Apple shows how such an automatic update can be achieved.

In your case, you should add the following methods to the managed object subclass ToDoItem:

- (void)setTodoDueDate:(NSDate *)newDate
{
    // If the todoDueDate changes, the section identifier become invalid.
    [self willChangeValueForKey:@"todoDueDate"];
    [self setPrimitiveValue:newDate forKey:@"todoDueDate"];
    [self didChangeValueForKey:@"todoDueDate"];

    // Set the section identifier to nil, so that it will be recalculated
    // when the sectionIdentifier method is called the next time:
    [self setPrimitiveValue:nil forKey:@"sectionIdentifier"];
}

+ (NSSet *)keyPathsForValuesAffectingSectionIdentifier
{
    // If the value of todoDueDate changes, the section identifier may change as well.
    return [NSSet setWithObject:@"todoDueDate"];
}