How to filter NSFetchedResultsController (CoreData) with UISearchDisplayController/UISearchBar
I'm trying to implement search code in my CoreData-based iPhone app. I'm not sure how to proceed. The app already has an NSFetchedResultsController with a predicate to retrieve the data for the primary TableView. I want to make sure I'm on the right path before I change too much code. I'm confused because so many of the examples are array-based instead of CoreData.
Here are some questions:
Do I need to have a second NSFetchedResultsController that retrieves only the matching items or can I use the same one as the primary TableView?
If I use the same one, is it as simple as clearing the FRC cache and then changing the predicate in the handleSearchForTerm:searchString method? Does the predicate have to contain the initial predicate as well as the search terms or does it remember that it used a predicate to retrieve data in the first place?
How do I get back to the original results? Do I just set the search predicate to nil? Won't that kill the original predicate that was used to retrieve the FRC results in the first place?
If anyone has any examples of code using search with the FRC, I would greatly appreciate it!
Answer
I actually just implemented this on one of my projects (your question and the other wrong answer hinted at what to do). I tried Sergio's answer but had exception issues when actually running on a device.
Yes you create two fetch results controllers: one for the normal display and another one for the UISearchBar's table view.
If you only use one FRC (NSFetchedResultsController) then the original UITableView (not the search table view that is active while searching) will possibly have callbacks called while you are searching and try to incorrectly use the filtered version of your FRC and you will see exceptions thrown about incorrect number of sections or rows in sections.
Here is what I did: I have two FRCs available as properties fetchedResultsController and searchFetchedResultsController. The searchFetchedResultsController should not be used unless there is a search (when the search is canceled you can see below that this object is released). All UITableView methods must figure out what table view it will query and which applicable FRC to pull the information from. The FRC delegate methods must also figure out which tableView to update.
It is surprising how much of this is boilerplate code.
Relevant bits of the header file:
@interface BlahViewController : UITableViewController <UISearchBarDelegate, NSFetchedResultsControllerDelegate, UISearchDisplayDelegate>
{
// other class ivars
// required ivars for this example
NSFetchedResultsController *fetchedResultsController_;
NSFetchedResultsController *searchFetchedResultsController_;
NSManagedObjectContext *managedObjectContext_;
// The saved state of the search UI if a memory warning removed the view.
NSString *savedSearchTerm_;
NSInteger savedScopeButtonIndex_;
BOOL searchWasActive_;
}
@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain, readonly) NSFetchedResultsController *fetchedResultsController;
@property (nonatomic, copy) NSString *savedSearchTerm;
@property (nonatomic) NSInteger savedScopeButtonIndex;
@property (nonatomic) BOOL searchWasActive;
relevent bits of the implementation file:
@interface BlahViewController ()
@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;
@property (nonatomic, retain) NSFetchedResultsController *searchFetchedResultsController;
@property (nonatomic, retain) UISearchDisplayController *mySearchDisplayController;
@end
I created a helpful method to retrieve the correct FRC when working with all of the UITableViewDelegate/DataSource methods:
- (NSFetchedResultsController *)fetchedResultsControllerForTableView:(UITableView *)tableView
{
return tableView == self.tableView ? self.fetchedResultsController : self.searchFetchedResultsController;
}
- (void)fetchedResultsController:(NSFetchedResultsController *)fetchedResultsController configureCell:(UITableViewCell *)theCell atIndexPath:(NSIndexPath *)theIndexPath
{
// your cell guts here
}
- (UITableViewCell *)tableView:(UITableView *)theTableView cellForRowAtIndexPath:(NSIndexPath *)theIndexPath
{
CallTableCell *cell = (CallTableCell *)[theTableView dequeueReusableCellWithIdentifier:@"CallTableCell"];
if (cell == nil)
{
cell = [[[CallTableCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"CallTableCell"] autorelease];
}
[self fetchedResultsController:[self fetchedResultsControllerForTableView:theTableView] configureCell:cell atIndexPath:theIndexPath];
return cell;
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
NSInteger count = [[[self fetchedResultsControllerForTableView:tableView] sections] count];
return count;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
NSInteger numberOfRows = 0;
NSFetchedResultsController *fetchController = [self fetchedResultsControllerForTableView:tableView];
NSArray *sections = fetchController.sections;
if(sections.count > 0)
{
id <NSFetchedResultsSectionInfo> sectionInfo = [sections objectAtIndex:section];
numberOfRows = [sectionInfo numberOfObjects];
}
return numberOfRows;
}
Delegate methods for the search bar:
#pragma mark -
#pragma mark Content Filtering
- (void)filterContentForSearchText:(NSString*)searchText scope:(NSInteger)scope
{
// update the filter, in this case just blow away the FRC and let lazy evaluation create another with the relevant search info
self.searchFetchedResultsController.delegate = nil;
self.searchFetchedResultsController = nil;
// if you care about the scope save off the index to be used by the serchFetchedResultsController
//self.savedScopeButtonIndex = scope;
}
#pragma mark -
#pragma mark Search Bar
- (void)searchDisplayController:(UISearchDisplayController *)controller willUnloadSearchResultsTableView:(UITableView *)tableView;
{
// search is done so get rid of the search FRC and reclaim memory
self.searchFetchedResultsController.delegate = nil;
self.searchFetchedResultsController = nil;
}
- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchString:(NSString *)searchString
{
[self filterContentForSearchText:searchString
scope:[self.searchDisplayController.searchBar selectedScopeButtonIndex]];
// Return YES to cause the search result table view to be reloaded.
return YES;
}
- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchScope:(NSInteger)searchOption
{
[self filterContentForSearchText:[self.searchDisplayController.searchBar text]
scope:[self.searchDisplayController.searchBar selectedScopeButtonIndex]];
// Return YES to cause the search result table view to be reloaded.
return YES;
}
make sure that you use the correct table view when getting updates from the FRC delegate methods:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
UITableView *tableView = controller == self.fetchedResultsController ? self.tableView : self.searchDisplayController.searchResultsTableView;
[tableView beginUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller
didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
atIndex:(NSUInteger)sectionIndex
forChangeType:(NSFetchedResultsChangeType)type
{
UITableView *tableView = controller == self.fetchedResultsController ? self.tableView : self.searchDisplayController.searchResultsTableView;
switch(type)
{
case NSFetchedResultsChangeInsert:
[tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeDelete:
[tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
break;
}
}
- (void)controller:(NSFetchedResultsController *)controller
didChangeObject:(id)anObject
atIndexPath:(NSIndexPath *)theIndexPath
forChangeType:(NSFetchedResultsChangeType)type
newIndexPath:(NSIndexPath *)newIndexPath
{
UITableView *tableView = controller == self.fetchedResultsController ? self.tableView : self.searchDisplayController.searchResultsTableView;
switch(type)
{
case NSFetchedResultsChangeInsert:
[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeDelete:
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:theIndexPath] withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeUpdate:
[self fetchedResultsController:controller configureCell:[tableView cellForRowAtIndexPath:theIndexPath] atIndexPath:theIndexPath];
break;
case NSFetchedResultsChangeMove:
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:theIndexPath] withRowAnimation:UITableViewRowAnimationFade];
[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade];
break;
}
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
UITableView *tableView = controller == self.fetchedResultsController ? self.tableView : self.searchDisplayController.searchResultsTableView;
[tableView endUpdates];
}
Other view information:
- (void)loadView
{
[super loadView];
UISearchBar *searchBar = [[[UISearchBar alloc] initWithFrame:CGRectMake(0, 0, self.tableView.frame.size.width, 44.0)] autorelease];
searchBar.autoresizingMask = (UIViewAutoresizingFlexibleWidth);
searchBar.autocorrectionType = UITextAutocorrectionTypeNo;
self.tableView.tableHeaderView = searchBar;
self.mySearchDisplayController = [[[UISearchDisplayController alloc] initWithSearchBar:searchBar contentsController:self] autorelease];
self.mySearchDisplayController.delegate = self;
self.mySearchDisplayController.searchResultsDataSource = self;
self.mySearchDisplayController.searchResultsDelegate = self;
}
- (void)didReceiveMemoryWarning
{
self.searchWasActive = [self.searchDisplayController isActive];
self.savedSearchTerm = [self.searchDisplayController.searchBar text];
self.savedScopeButtonIndex = [self.searchDisplayController.searchBar selectedScopeButtonIndex];
fetchedResultsController_.delegate = nil;
[fetchedResultsController_ release];
fetchedResultsController_ = nil;
searchFetchedResultsController_.delegate = nil;
[searchFetchedResultsController_ release];
searchFetchedResultsController_ = nil;
[super didReceiveMemoryWarning];
}
- (void)viewDidDisappear:(BOOL)animated
{
// save the state of the search UI so that it can be restored if the view is re-created
self.searchWasActive = [self.searchDisplayController isActive];
self.savedSearchTerm = [self.searchDisplayController.searchBar text];
self.savedScopeButtonIndex = [self.searchDisplayController.searchBar selectedScopeButtonIndex];
}
- (void)viewDidLoad
{
// restore search settings if they were saved in didReceiveMemoryWarning.
if (self.savedSearchTerm)
{
[self.searchDisplayController setActive:self.searchWasActive];
[self.searchDisplayController.searchBar setSelectedScopeButtonIndex:self.savedScopeButtonIndex];
[self.searchDisplayController.searchBar setText:savedSearchTerm];
self.savedSearchTerm = nil;
}
}
FRC creation code:
- (NSFetchedResultsController *)newFetchedResultsControllerWithSearch:(NSString *)searchString
{
NSArray *sortDescriptors = // your sort descriptors here
NSPredicate *filterPredicate = // your predicate here
/*
Set up the fetched results controller.
*/
// Create the fetch request for the entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *callEntity = [MTCall entityInManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:callEntity];
NSMutableArray *predicateArray = [NSMutableArray array];
if(searchString.length)
{
// your search predicate(s) are added to this array
[predicateArray addObject:[NSPredicate predicateWithFormat:@"name CONTAINS[cd] %@", searchString]];
// finally add the filter predicate for this view
if(filterPredicate)
{
filterPredicate = [NSCompoundPredicate andPredicateWithSubpredicates:[NSArray arrayWithObjects:filterPredicate, [NSCompoundPredicate orPredicateWithSubpredicates:predicateArray], nil]];
}
else
{
filterPredicate = [NSCompoundPredicate orPredicateWithSubpredicates:predicateArray];
}
}
[fetchRequest setPredicate:filterPredicate];
// Set the batch size to a suitable number.
[fetchRequest setFetchBatchSize:20];
[fetchRequest setSortDescriptors:sortDescriptors];
// Edit the section name key path and cache name if appropriate.
// nil for section name key path means "no sections".
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:self.managedObjectContext
sectionNameKeyPath:nil
cacheName:nil];
aFetchedResultsController.delegate = self;
[fetchRequest release];
NSError *error = nil;
if (![aFetchedResultsController performFetch:&error])
{
/*
Replace this implementation with code to handle the error appropriately.
abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
*/
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return aFetchedResultsController;
}
- (NSFetchedResultsController *)fetchedResultsController
{
if (fetchedResultsController_ != nil)
{
return fetchedResultsController_;
}
fetchedResultsController_ = [self newFetchedResultsControllerWithSearch:nil];
return [[fetchedResultsController_ retain] autorelease];
}
- (NSFetchedResultsController *)searchFetchedResultsController
{
if (searchFetchedResultsController_ != nil)
{
return searchFetchedResultsController_;
}
searchFetchedResultsController_ = [self newFetchedResultsControllerWithSearch:self.searchDisplayController.searchBar.text];
return [[searchFetchedResultsController_ retain] autorelease];
}