Fixed Static Cell in UICollectionView - ios

Question

In my iPad application, I have used a UICollectionView which displays different notes saved by the user in core data through NSFetchedResultsController.
According to the design, I must have to show a cell with control to add new note in core data. Once the note is added it is displayed as the 2nd cell in the collection view.
I tried to implement it in following manner;
#pragma mark - UICollectionViewDataSource
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView*)collectionView
{
return self.fetchedResultsController.sections.count?:1;
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection: (NSInteger)section
{
id<NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
return [sectionInfo numberOfObjects]?:1;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
if (indexPath.section == 0 && indexPath.item == 0)
{
AddNewNoteCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"AddNewNoteCell" forIndexPath:indexPath];
cell.delegate = self;
return cell;
}
else
{
NoteCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"NoteCell" forIndexPath:indexPath];
//Code for customization
return cell;
}
}
But this approach is causing problems. It doesn't add the newly created note cell immediately. If it adds, the newly added cell is displayed as "Add new cell". If I pop the view controller and load the view controller again it displays the cells correctly.
Please guide me for an accurate solution.
Is this possible?

Answer 1

Assuming you want the "add new note" cell to appear as the first item in the first section, but not in any other sections, you need to modify your numberOfItemsInSection method to add 1 to the [sectionInfo numberOfObjects] for section 0. For the other sections, you should just return the numberOfObjects:
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection: (NSInteger)section
{
id<NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
NSInteger items = [sectionInfo numberOfObjects];
if (section == 0) items++;
return items;
}
Then in cellForItemAtIndexPath: you can (as you have) treat item 0 in section 0 as your special case (i.e. give it a different cell subclass and configure it accordingly). For the other cells, you can configure them using the indexPath to get details from your fetchedResultsController. However, in section 0, you need to adjust this: cell 0 is your "Add new note" cell, so you want cell 1 to be configured with the details of item 0 from your fetchedResultsController. Construct a new indexPath:
NSIndexPath *fetchIndexPath = [NSIndexPath indexPathForItem:(indexPath.row -1) inSection:0];
and use that to get the correct data from your fetchedResultsController.
I assume your "Add new note" cell calls some method in your view controller to add the new note object to your managedObjectContext. If you implement the NSFetchedResultsController delegate methods (see docs), you can immediately update your collectionView with the newly added object. But you must reverse the above adjustment for section 0:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
[self.collectionView beginUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type
{
switch(type) {
case NSFetchedResultsChangeInsert:
[self.collectionView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex]];
break;
case NSFetchedResultsChangeDelete:
[self.collectionView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex]];
break;
}
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath
{
NSIndexPath *adjustedIndexPath;
NSIndexPath *adjustedNewIndexPath;
if (indexPath.section == 0) {
adjustedIndexPath = [NSIndexPath indexPathForItem:(indexPath.row+1) inSection:0];
adjustedNewIndexPath = [NSIndexPath indexPathForItem:(newIndexPath.row+1) inSection:0];
indexPath = adjustedIndexPath;
newIndexPath = adjustedNewIndexPath;
}
switch(type) {
case NSFetchedResultsChangeInsert:
[self.collectionView insertItemsAtIndexPaths:#[newIndexPath]];
break;
case NSFetchedResultsChangeDelete:
[self.collectionView deleteItemsAtIndexPaths:#[indexPath]];
break;
case NSFetchedResultsChangeUpdate:
[self configureCell:[self.collectionView cellForItemAtIndexPath:indexPath] atIndexPath:indexPath];
break;
case NSFetchedResultsChangeMove:
[self.collectionView moveItemAtIndexPath:indexPath toIndexPath:newIndexPath];
break;
}
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
[self.collectionView endUpdates];
}
You should tailor the above methods to suit your particular needs (eg. I assume you don't want to permit a section to be moved ahead of section 0).