Adding extra sections to a NSFetchedResultsController - iphone

Question

I'm writing a small iPhone app for my company that shows bookings for each employee one week at a time. I'm using core data to get a list of 'Bookings' for a given week and want to display them in a UITableView broken down in to one section per day of the week.
The problem comes in that I need to show 7 sections for each day of the week (showing a 'No Bookings' cell where a section/date has no bookings).
I've got a screenshot of the app as it stands here (sorry can't post images yet as I'm new to StackOverlow)
At the moment I'm achieving this by using a 'fetchResults' method which gets the bookings and organises them in to an array of possible dates:
- (void)refetchResults {
// Drop bookings Array, replacing with new empty one
// 7 slots for 7 days each holding mutable array to recieve bookings where appropraite
self.bookings = [NSArray arrayWithObjects:[NSMutableArray array],
[NSMutableArray array], [NSMutableArray array],
[NSMutableArray array], [NSMutableArray array],
[NSMutableArray array], [NSMutableArray array], nil];
// Create the fetch request for the entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Booking" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
// Limit to this weeks data
[fetchRequest setPredicate:
[NSPredicate predicateWithFormat:#"(date >= %#) && (date <= %#) && (resource == %#)",
firstDate,lastDate,resourceId]];
// Edit the sort key as appropriate.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"date" ascending:YES];
NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:#"recId" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, sortDescriptor2, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
// Fetch records in to array
NSError *error;
NSArray *results = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
if (results == nil) {
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
[fetchRequest release];
[sortDescriptor release];
[sortDescriptor2 release];
[sortDescriptors release];
// Walk through records and place in bookings Array as required
for (Booking *item in results) {
// Decide on array index by difference in firstDate and booking date
int idx = (int)[[item date] timeIntervalSinceDate:firstDate]/86400;
// Add the item to the approp MutArray
[(NSMutableArray *)[bookings objectAtIndex:idx] addObject:item];
}
// Reload table
[tableView reloadData];
}
My question is: is there any way to achieve the same result using NSFetchedResultsController? Somehow I'd need to get the NSFetchedResultsController to have 7 sections, one for each day of the week, some of them possibly having no bookings.
Any help much appreciated :)

Answer 1

So, being as the weather isn't very nice outside I've had a go at answering my own question and implementing the 'workaround' described in my reply to westsider.
The idea is to hold a 'mapping' array (just a simple 7 slot int array) which will map the section the tableview will ask for to the underlying fetchedresultscontroller section. Each array slot will have the appropriate section index or '-1' where there are no underlying sections (and where a 'No Booking' cell should be shown instead).
So, my refetchResults method becomes:
- (void)refetchResults {
// Create the fetch request for the entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Booking" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
// Limit to this weeks data
[fetchRequest setPredicate:
[NSPredicate predicateWithFormat:#"(date >= %#) && (date <= %#) && (resource == %#)",
firstDate,lastDate,resourceId]];
// Edit the sort key as appropriate.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"date" ascending:YES];
NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:#"recId" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, sortDescriptor2, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
// Set up FRC
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:#"date" cacheName:nil];
self.fetchedResultsController = aFetchedResultsController;
self.fetchedResultsController.delegate = self;
[aFetchedResultsController release];
[fetchRequest release];
[sortDescriptor release];
[sortDescriptor2 release];
[sortDescriptors release];
// Run up FRC
NSError *error = nil;
if (![fetchedResultsController_ performFetch:&error]) {
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
// Update FRC map
[self updateFRCMap];
// Reload table
[tableView reloadData];
}
The mapping is set in the following method. This is called whenever the mapping needs to be refreshed - for example when I get callbacks from the fetchedresultscontroller for items that have been added/deleted/etc.
- (void)updateFRCMap {
// Set mapping table for seven days of week to appropriate section in frc
for (int idx=0;idx<7;idx++) { frcMap[idx] = -1; } // Reset mappings
// For each section
for (int sidx=0; sidx<[[self.fetchedResultsController sections] count]; sidx++)
{
// If section has items
if ([[[self.fetchedResultsController sections] objectAtIndex:sidx] numberOfObjects] > 0)
{
// Look at first booking of section to get date
NSDate *date = [(Booking *)[self.fetchedResultsController objectAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:sidx]] date];
// Decide on array index by difference in firstDate and booking date
int idx = (int)[date timeIntervalSinceDate:firstDate]/86400;
// Set map
frcMap[idx] = sidx;
}
}
}
This can probably be optimised a bit but works OK for now. I suspect it might suffer GMT/BST clock change problems which will need fixing ... not that clock change problems are all that urgent, eh Apple? ;P
After that it's just a case of using the mapping array when responding to the tableview:
#pragma mark -
#pragma mark Table view data source
// Gets the booking from the fetchedResultsController using a remapped indexPath
- (Booking *)bookingForMappedIndexPath:(NSIndexPath *)indexPath {
return (Booking *)[self.fetchedResultsController objectAtIndexPath:
[NSIndexPath indexPathForRow:indexPath.row inSection:frcMap[indexPath.section]]];
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return 7; // 7 days viewed
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
// Rows in section or 1 if no section
if (frcMap[section] != -1) {
id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:frcMap[section]];
return [sectionInfo numberOfObjects];
} else {
return 1;
}
}
- (UITableViewCell *)tableView:(UITableView *)_tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *CellIdentifier = #"RegularCell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease];
}
// Configure the cell.
[self configureCell:cell atIndexPath:indexPath];
return cell;
}
- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {
// If no actual bookings for section then its a blank cell
if (frcMap[indexPath.section] == -1) {
// Configure a blank cell.
cell.textLabel.text = #"No Bookings";
cell.detailTextLabel.text = #"";
cell.textLabel.font = [UIFont systemFontOfSize:16];
cell.textLabel.textColor = [UIColor lightGrayColor];
cell.accessoryType = UITableViewCellAccessoryNone;
cell.selectionStyle = UITableViewCellSelectionStyleNone;
} else {
// Regular cell
Booking *booking = [self bookingForMappedIndexPath:indexPath];
cell.textLabel.text = booking.desc;
cell.detailTextLabel.text = [NSString stringWithFormat:#"%# %#", booking.location, booking.detail];
cell.textLabel.font = [UIFont systemFontOfSize:14];
cell.textLabel.textColor = [UIColor darkTextColor];
cell.detailTextLabel.font = [UIFont systemFontOfSize:12];
cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
cell.selectionStyle = UITableViewCellSelectionStyleBlue;
}
}
Any comments or better ways of writing this are very much welcome :)

Answer 2

I haven't used this much, but you might check out NSFetchedResultsSectionInfo protocol. It can be used like this, apparently:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
NSInteger numberOfRows = 0;
if ([[fetchedResultsController sections] count] > 0)
{
id <NSFetchedResultsSectionInfo> sectionInfo = [[fetchedResultsController sections] objectAtIndex:section];
numberOfRows = [sectionInfo numberOfObjects];
}
return numberOfRows;
}
Good luck.

Answer 3

I had this problem too. I've written a subclass of NSFetchedResultsController to solve the issue:
https://github.com/timothyarmes/TAFetchedResultsController
Tim