Weird Header Error when using NSFetchedResultsController - iphone

Question

Since I can't really describe this error, I recorded my screen with the error.
http://www.youtube.com/watch?v=w2FqKKcL2Ck&feature=youtu.be
Basically I am not sure what to do. When the user finishes all the tasks in the Tasks To Complete section, I would like the section header to remain there...just with no objects in it (simply because its needed in order to add more tasks).
Luckily when the user doesn't have any Completed Tasks, the header there disappears which is what should happen. I would like the top header to not disappear though...
Also, same thing with the delete. I don't really want the Tasks To Complete section to disappear completely when the last object is deleted.
I've heard this is not possible unless you use a custom subclass like TAFetchResultsController, but I tried using that and it was just too complex for me to implement (and kind of broke my application rather than fix it). Maybe you guys have some suggestions?
Here is some relevant code:
Tasks core data properties
#interface Tasks : NSManagedObject
#property (nonatomic, retain) NSString *sectionString;
#end
#implementation Tasks
#dynamic sectionString;
#end
adding tasks to different sections
NSManagedObjectContext *context = self.managedObjectContext;
NSManagedObject *startingTask = [NSEntityDescription insertNewObjectForEntityForName:#"Tasks" inManagedObjectContext:context];
[startingTask setValue:#"Eat Dinner" forKey:#"taskName"];
[startingTask setValue:[NSNumber numberWithDouble:400] forKey:#"timeInterval"];
[startingTask setValue:#"Tasks To Complete" forKey:#"sectionString"];
NSManagedObject *finishedTask = [NSEntityDescription insertNewObjectForEntityForName:#"Tasks" inManagedObjectContext:context];
[finishedTask setValue:#"Do Laundry" forKey:#"taskName"];
[finishedTask setValue:[NSNumber numberWithDouble:400] forKey:#"timeInterval"];
[finishedTask setValue:#"Completed Tasks" forKey:#"sectionString"];
NSError *error;
if (![context save:&error]) {
NSLog(#"couldn't save: %#", [error localizedDescription]);
}
TableViewController.m:
-(void) viewDidLoad{
// ---Start Core Data With NSFetchedResultsController---
[super viewDidLoad];
NSError *error;
if (![[self fetchedResultsController] performFetch:&error]){
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
exit(-1);
}
// ---End Core Data w/ NSFetchedResultsController---
[self.tableView setDelegate:self];
[self setModalTransitionStyle:UIModalTransitionStyleCrossDissolve];
holdViewsArray = [[NSMutableArray alloc]init];
UIView *seperatorView;
UIView *seperatorView2;
NSString *sectionTitle = #"Tasks To Complete";
NSString *section2Title = #"Completed Tasks";
UILabel *label = [[UILabel alloc]init];
UILabel *label2 = [[UILabel alloc]init];
label.frame = CGRectMake(10.0, 5.0, 320.0, 50.0);
label.text = sectionTitle;
label2.frame = CGRectMake(10.0, 0.0, 320.0, 40.0);
label2.text = section2Title;
headerView = [[UIView alloc]initWithFrame:label.frame];
headerView2 = [[UIView alloc]initWithFrame:label2.frame];
CGRect sepFrame = CGRectMake(0, headerView.frame.size.height-2, 320, 1);
CGRect sep2Frame =CGRectMake(0, headerView2.frame.size.height-2, 320, 1);
seperatorView = [[UIView alloc] initWithFrame:sepFrame];
seperatorView2 = [[UIView alloc]initWithFrame:sep2Frame];
[headerView addSubview:seperatorView];
[headerView2 addSubview:seperatorView2];
[headerView addSubview:label];
[headerView addSubview:button];
[headerView2 addSubview:label2];
[holdViewsArray addObject:headerView];
[holdViewsArray addObject:headerView2];
- (NSFetchedResultsController *)fetchedResultsController {
if (_fetchedResultsController != nil) {
return _fetchedResultsController;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
entityForName:#"Tasks" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
NSSortDescriptor *isCompleted = [[NSSortDescriptor alloc]initWithKey:#"sectionString" ascending:NO];
NSSortDescriptor *sort = [[NSSortDescriptor alloc]
initWithKey:#"dateCreated" ascending:YES];
[fetchRequest setSortDescriptors:#[isCompleted, sort]];
[fetchRequest setFetchBatchSize:20];
NSFetchedResultsController *theFetchedResultsController =
[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:managedObjectContext sectionNameKeyPath:#"sectionString"
cacheName:nil];
self.fetchedResultsController = theFetchedResultsController;
_fetchedResultsController.delegate = self;
return _fetchedResultsController;
}-(void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {
Tasks *task = [_fetchedResultsController objectAtIndexPath:indexPath];
cell.textLabel.text = task.taskName.uppercaseString;
cell.detailTextLabel.text = [NSString stringWithFormat:#"%.0f", task.timeInterval];
cell.imageView.image = [UIImage imageNamed:#"unchecked.png"];
cell.imageView.highlightedImage = [UIImage imageNamed:#"uncheckedhighlighted.png"];
[cell setAccessoryType:UITableViewCellAccessoryDisclosureIndicator];
if (indexPath.section == 1)
[cell.contentView setAlpha:0.5];
else {
[cell.contentView setAlpha:1];
}
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc]initWithTarget:self action:#selector(handlechecking:)];
[cell.imageView addGestureRecognizer:tap];
cell.imageView.userInteractionEnabled = YES;
}
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
cellSubclassCell *cell = [tableView dequeueReusableCellWithIdentifier:#"UITableViewCell"];
if (!cell)
cell = [[cellSubclassCell alloc]initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:#"UITableViewCell"];
[self configureCell:cell atIndexPath:indexPath];
return cell;
}
-(void)handlechecking:(UITapGestureRecognizer *)t{
CGPoint tapLocation = [t locationInView:self.tableView];
NSIndexPath *tappedIndexPath = [self.tableView indexPathForRowAtPoint:tapLocation];
Tasks *task = [_fetchedResultsController objectAtIndexPath:tappedIndexPath];
if ([task.sectionString isEqual: #"Tasks To Complete"]){
task.sectionString = #"Completed Tasks";
} else if ([task.sectionString isEqualToString:#"Completed Tasks"]){
task.sectionString = #"Tasks To Complete";
}
[self.tableView reloadData];
NSTimeInterval time = [[NSDate date] timeIntervalSinceReferenceDate];
[task setDateCreated:time];
}
-(UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section{
switch (section) {
case 0:
return [holdViewsArray objectAtIndex:0];
break;
case 1:
return [holdViewsArray objectAtIndex:1];
break;
}
return 0;
}

Answer 1

NSFetchedResultsController infers sections from the objects returned by the fetch. So if the number of items a section goes to zero, the section vanishes. That's just how NSFetchedResultsController works.
Your simplest option is probably a 3rd-party framework. Take a look at TLIndexPathTools. It provides an alternative to NSFetchedResultsController that does not require Core Data or an NSFetchRequest, meaning you can use it in more scenarios. Take a look at some of the example projects (the Core Data one is called "Core Data")- some cool things are done with few lines of code.
TLIndexPathTools supports empty sections, but not explicitly in the way you need. However, you can accomplish it with a few lines of code by overriding TLIndexPathController. The code would look something like this:
#interface MyIndexPathController : TLIndexPathController
#end
#import "MyIndexPathController.h"
#implementation MyIndexPathController
- (void)setDataModel:(TLIndexPathDataModel *)dataModel
{
if ([dataModel sectionForSectionName:#"MyFirstSectionName"] == NSNotFound) {
TLIndexPathSectionInfo *firstSection = [[TLIndexPathSectionInfo alloc] initWithItems:nil andName:#"MyFirstSectionName"];
NSMutableArray *sectionInfos = [NSMutableArray arrayWithArray:dataModel.sections];
[sectionInfos insertObject:firstSection atIndex:0];
dataModel = [[TLIndexPathDataModel alloc] initWithSectionInfos:sectionInfos andIdentifierKeyPath:dataModel.identifierKeyPath andCellIdentifierKeyPath:dataModel.cellIdentifierKeyPath];
}
super.dataModel = dataModel;
}
#end
What is happening here is we intercept the data model generated by the controller (based on the results of our fetch request) and check if the section of interest is present. If not, we create an empty section info object and combine it with the other section infos into a new data model and pass it along to the super class.
It should not be too difficult to extend generically to work with any set of required sections if needed.