How to filter NSFetchedResultsController (CoreData

问题:

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:

1. 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?

2. 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?

3. 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!

回答1:

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];
}   

回答2:

Some have commented that this can be done with a single NSFetchedResultsController. That\'s what I did, and here are the details. This solution assumes you just want to filter down the table and maintain all other aspects (sort order, cell layout, etc.) of the search results.

First, define two properties in your UITableViewController subclass (with the appropriate @synthesize and dealloc, if applicable):

@property (nonatomic, retain) UISearchDisplayController *searchController;
@property (nonatomic, retain) NSString *searchString;

Second, initialize the search bar in the viewDidLoad: method of your UITableViewController subclass:

UISearchBar *searchBar = [[UISearchBar alloc] initWithFrame:CGRectMake(0,0,self.tableView.frame.size.width,44)]; 
searchBar.placeholder = @\"Search\";
searchBar.delegate = self;
self.searchController = [[[UISearchDisplayController alloc] initWithSearchBar:searchBar contentsController:self] autorelease];
self.searchController.delegate = self;
self.searchController.searchResultsDataSource = self;   
self.searchController.searchResultsDelegate = self; 
self.tableView.tableHeaderView = self.searchController.searchBar;
[searchBar release];

Third, implement the UISearchDisplayController delegate methods like this:

// This gets called when you start typing text into the search bar
-(BOOL)searchDisplayController:(UISearchDisplayController *)_controller shouldReloadTableForSearchString:(NSString *)_searchString {
   self.searchString = _searchString;
   self.fetchedResultsController = nil;
   return YES;
}

// This gets called when you cancel or close the search bar
-(void)searchDisplayController:(UISearchDisplayController *)controller willUnloadSearchResultsTableView:(UITableView *)tableView {
   self.searchString = nil;
   self.fetchedResultsController = nil;
   [self.tableView reloadData];
}

Finally, in the fetchedResultsController method change the NSPredicate depending if self.searchString is defined:

-(NSFetchedResultsController *)fetchedResultsController {
   if (fetchedResultsController == nil) {

       // removed for brevity

      NSPredicate *predicate;

      if (self.searchString) {
         // predicate that uses searchString (used by UISearchDisplayController)
         // e.g., [NSPredicate predicateWithFormat:@\"name CONTAINS[cd] %@\", self.searchString];
          predicate = ... 
      } else {
         predicate = ... // predicate without searchString (used by UITableViewController)
      }

      // removed for brevity

   }

   return fetchedResultsController;
} 

回答3:

It took me a few tries to get this working...

My key to understanding was realizing that there are two tableViews at work here. One managed by my viewcontroller and one managed by the searchviewcontroller and then I could test to see which is active and do the right thing. The documentation was helpful too:

http://developer.apple.com/library/ios/#documentation/uikit/reference/UISearchDisplayController_Class/Reference/Reference.html

Here\'s what I did -

Added the searchIsActive flag:

@interface ItemTableViewController : UITableViewController <NSFetchedResultsControllerDelegate, UISearchDisplayDelegate, UISearchBarDelegate> {

    NSString *sectionNameKeyPath;
    NSArray *sortDescriptors;


@private
    NSFetchedResultsController *fetchedResultsController_;
    NSManagedObjectContext *managedObjectContext_;

    BOOL searchIsActive;

}

@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;
@property (nonatomic, retain) NSString *sectionNameKeyPath;
@property (nonatomic, retain) NSArray *sortDescriptors;
@property (nonatomic) BOOL searchIsActive;

Added the synthesize in the implementation file.

Then I added these methods to for searching:

#pragma mark -
#pragma mark Content Filtering

- (void)filterContentForSearchText:(NSString*)searchText scope:(NSString*)scope
{
    NSFetchRequest *aRequest = [[self fetchedResultsController] fetchRequest];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@\"name BEGINSWITH[cd] %@\", searchText];

    [aRequest setPredicate:predicate];

    NSError *error = nil;
    if (![[self fetchedResultsController] performFetch:&error]) {
        // Handle error
        NSLog(@\"Unresolved error %@, %@\", error, [error userInfo]);
        abort();
    }  

}

#pragma mark -
#pragma mark UISearchDisplayController Delegate Methods

- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchString:(NSString *)searchString
{
    [self filterContentForSearchText:[self.searchDisplayController.searchBar text] scope:nil];

    return YES;
}

/*
- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchScope:(NSInteger)searchOption
{
    return YES;
}
*/

- (void)searchDisplayControllerWillBeginSearch:(UISearchDisplayController *)controller {
    [self setSearchIsActive:YES];
    return;
}

- (void)searchDisplayControllerDidEndSearch:(UISearchDisplayController *)controller 
{
    NSFetchRequest *aRequest = [[self fetchedResultsController] fetchRequest];

    [aRequest setPredicate:nil];

    NSError *error = nil;
    if (![[self fetchedResultsController] performFetch:&error]) {
        // Handle error
        NSLog(@\"Unresolved error %@, %@\", error, [error userInfo]);
        abort();
    }  

    [self setSearchIsActive:NO];
    return;
}

Then in controllerWillChangeContent:

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller 
{
    if ([self searchIsActive]) {
        [[[self searchDisplayController] searchResultsTableView] beginUpdates];
    }
    else  {
        [self.tableView beginUpdates];
    }
}

And controllerDidChangeContent:

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller 
{
    if ([self searchIsActive]) {
        [[[self searchDisplayController] searchResultsTableView] endUpdates];
    }
    else  {
        [self.tableView endUpdates];
    }
}

And delete the cache when resetting the predicate.

Hope this helps.

回答4:

I faced with the same task and found THE SIMPLEST WAY POSSIBLE to solve it. Shortly: you need to define one more method, very similar to -fetchedResultsController with a custom compound predicate.

In my personal case my -fetchedResultsController looks like this:

- (NSFetchedResultsController *) fetchedResultsController
{
    if (fetchedResultsController != nil)
    {
        return fetchedResultsController;
    }
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@\"Client\"
                                              inManagedObjectContext:[[PTDataManager sharedManager] managedObjectContext]];
    [fetchRequest setEntity:entity];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@\"agency_server_id == %@\", agency.server_id];
    fetchRequest.predicate = predicate;

    NSSortDescriptor *sortByName1Descriptor = [[NSSortDescriptor alloc] initWithKey:@\"lastname\" ascending:YES];
    NSSortDescriptor *sortByName2Descriptor = [[NSSortDescriptor alloc] initWithKey:@\"firstname\" ascending:YES];
    NSSortDescriptor *sortByName3Descriptor = [[NSSortDescriptor alloc] initWithKey:@\"middlename\" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects: sortByName1Descriptor, sortByName2Descriptor, sortByName3Descriptor, nil];

    fetchRequest.sortDescriptors = sortDescriptors;

    fetchedResultsController = [[NSFetchedResultsController alloc]initWithFetchRequest:fetchRequest managedObjectContext:[[PTDataManager sharedManager] managedObjectContext] sectionNameKeyPath:nil cacheName:nil];
    fetchedResultsController.delegate = self;
    return fetchedResultsController;
}

As you can see I am fetching clients of one agency filtered by agency.server_id predicate. As a result I am retrieving my content in a tableView (all related to implementation of tableView and fetchedResultsController code is pretty standard) as well. To implement searchField I am defining a UISearchBarDelegate delegate method. I am triggering it with search method, say -reloadTableView:

- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
{
    [self reloadTableView];
}

and of course definition of -reloadTableView:

- (void)reloadTableView
{
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@\"Client\"
                                              inManagedObjectContext:[[PTDataManager sharedManager] managedObjectContext]];
    [fetchRequest setEntity:entity];

    NSSortDescriptor *sortByName1Descriptor = [[NSSortDescriptor alloc] initWithKey:@\"lastname\" ascending:YES];
    NSSortDescriptor *sortByName2Descriptor = [[NSSortDescriptor alloc] initWithKey:@\"firstname\" ascending:YES];
    NSSortDescriptor *sortByName3Descriptor = [[NSSortDescriptor alloc] initWithKey:@\"middlename\" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects: sortByName1Descriptor, sortByName2Descriptor, sortByName3Descriptor, nil];
    fetchRequest.sortDescriptors = sortDescriptors;

    NSPredicate *idPredicate = [NSPredicate predicateWithFormat:@\"agency_server_id CONTAINS[cd] %@\", agency.server_id];
    NSString *searchString = self.searchBar.text;
    if (searchString.length > 0)
    {
        NSPredicate *firstNamePredicate = [NSPredicate predicateWithFormat:@\"firstname CONTAINS[cd] %@\", searchString];
        NSPredicate *lastNamePredicate = [NSPredicate predicateWithFormat:@\"lastname CONTAINS[cd] %@\", searchString];
        NSPredicate *middleNamePredicate = [NSPredicate predicateWithFormat:@\"middlename CONTAINS[cd] %@\", searchString];
        NSPredicate *orPredicate = [NSCompoundPredicate orPredicateWithSubpredicates:[NSArray arrayWithObjects:firstNamePredicate, lastNamePredicate, middleNamePredicate, nil]];
        NSPredicate *andPredicate = [NSCompoundPredicate andPredicateWithSubpredicates:[NSArray arrayWithObjects:idPredicate, nil]];
        NSPredicate *finalPred = [NSCompoundPredicate andPredicateWithSubpredicates:[NSArray arrayWithObjects:orPredicate, andPredicate, nil]];
        [fetchRequest setPredicate:finalPred];
    }
    else
    {
        [fetchRequest setPredicate:idPredicate];
    }

    self.fetchedResultsController = [[NSFetchedResultsController alloc]initWithFetchRequest:fetchRequest managedObjectContext:[[PTDataManager sharedManager] managedObjectContext] sectionNameKeyPath:nil cacheName:nil];
    self.fetchedResultsController.delegate = self;

    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error])
    {
        NSLog(@\"Unresolved error %@, %@\", [error localizedDescription], [error localizedFailureReason]);
    }; 

    [self.clientsTableView reloadData];
}

This bunch of code is very similar to first, \"standard\" -fetchedResultsController BUT inside if-else statement here is:

+andPredicateWithSubpredicates: - using this method we can set a predicate to save results of our main first fetch in the tableView

+orPredicateWithSubpredicates - using this method we are filtering existing fetch by search query from searchBar

At the end I am setting array of predicates as a compound predicate for this particular fetch. AND for required predicates, OR for optional.

And that\'s all! You don\'t need to implement anything more. Happy coding!

回答5:

Are you using a live search?

If you are NOT, you probably want an array (or an NSFetchedResultsController) with the previous searches you used, when the user presses \"search\", you tell your FetchedResults to change its predicate.

Either way, you will need to rebuild your FetchedResults every time. I recommend using only one NSFetchedResultsController, since you\'ll have to duplicate your code a lot and you don\'t need to waste memory in something you\'re not showing.

Just make sure you have a NSString \"searchParameters\" variable and your FetchedResults method rebuilds it for you as needed, using the search parameters if available, you should just do:

a) set the \"searchParameters\" to something (or nil, if you want all the results).

b) release and set to nil the current NSFetchedResultsController object.

c) reload table data.

Here\'s a simple code:

- (void)searchString:(NSString*)s {
    self.searchResults = s;
    [fetchedResultsController release];
    fetchedResultsController = nil;
    [self.tableView reloadData];
}

-(NSFetchedResultsController *)fetchedResultsController {
    if (fetchedResultsController != nil) {
        return fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@\"EntityName\" inManagedObjectContext:self.context];
    [fetchRequest setEntity:entity];

    [fetchRequest setFetchBatchSize:20];

    // searchResults is a NSString*
    if (searchResults != nil) {
        NSPredicate *predicate = [NSPredicate predicateWithFormat:@\"name LIKE %@\",searchResults];
        [fetchRequest setPredicate:predicate];
    }

    fetchedResultsController = 
    [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
        managedObjectContext:self.context sectionNameKeyPath:nil 
        cacheName:nil];
    fetchedResultsController.delegate = self;

    [fetchRequest release];

    return fetchedResultsController;    
}

回答6:

Swift 3.0, UISearchController, NSFetchedResultsController and Core Data

This code will work on Swift 3.0 with Core Data! You\'ll need a single delegate method and a few lines of code for filtering and searching objects from the model. Nothing will be needed if you have implemented all of the FRC and their delegate methods as well as searchController.

The UISearchResultsUpdating protocol method

func updateSearchResults(for searchController: UISearchController) {

    let text = searchController.searchBar.text

    if (text?.isEmpty)! {
       // Do something 
    } else {
        self.fetchedResultsController.fetchRequest.predicate = NSPredicate(format: \"( someString contains[cd] %@ )\", text!)
    }
    do {
        try self.fetchedResultsController.performFetch()
        self.tableView.reloadData()
    } catch {}
}

That\'s it! Hope it helps you! Thanks

回答7:

SWIFT 3.0

Use a textField, UISearchDisplayController is deprecated as of iOS 8, you would have to use a UISearchController. Instead of dealing with the Search Controller, why dont you create your own search mechanism? You can customize it more and have more control over it, and not have to worry about SearchController changing and/or being deprecated.

This method I use works very well, and doesnt require much code. It does require you use Core Data and implement NSFetchedResultsController, however.

First, create a TextField and register it with a method:

searchTextField?.addTarget(self, action: #selector(textFieldDidChange), for: UIControlEvents.editingChanged)

Then create your textFieldDidChange method, described in the selector when the target was added:

func textFieldDidChange() {
    if let queryString = searchTextField.text {
        filterList(queryString)
        self.tableView.reloadData()
    }
}

Then you want to filter the list in filterList() method using NSPredicate or NSCompound predicate if it is more complex. In my filterList method, I am filtering based on the name of the entity, and the name of the entities \"subCategories\" object (a one to many relationship).

func filterList(_ queryString: String) {
    if let currentProjectID = Constants.userDefaults.string(forKey: Constants.CurrentSelectedProjectID) {
        if let currentProject = ProjectDBFacade.getProjectWithID(currentProjectID) {
            if (queryString != \"\"){
                let categoryPredicate = NSPredicate(format: \"name CONTAINS[c] %@ && project == %@\", queryString, currentProject)
                let subCategoryPredicate = NSPredicate(format: \"subCategories.name CONTAINS[c] %@ && project == %@\", queryString, currentProject)
                let orPredicate = NSCompoundPredicate(type: .or, subpredicates: [categoryPredicate, subCategoryPredicate])
                fetchedResultsController.fetchRequest.predicate = orPredicate
            }else{
                fetchedResultsController.fetchRequest.predicate = NSPredicate(format: \"project == %@\", currentProject)
            }

            do {
                try fetchedResultsController.performFetch()
            } catch {
                print(\"Error:  Could not fetch fetchedResultsController\")
            }
        }
    }
}

回答8:

I think Luka has a better approach for this. See LargeDataSetSample and his reason

He does not use FetchedResultsController, but uses cache when searching, hence the search results appears much faster when user types more in SearchBar

I\'ve used his approach in my app and it works OK. Also remember if you want to work with Model object, make it as simple as possible, see my answer about setPropertiesToFetch

回答9:

Here\'s a way of handling fetchedResults with multiple data sets that is both simple and general enough to apply almost anywhere. Simply grab your main results to an array when some condition is present.

NSArray *results = [self.fetchedResultsController fetchedObjects];

Query the array by looping through it or whatever you desire in order to create a subset of your main fetchedResults. And now you can either use the full set or subset when some condition is present.

回答10:

I really liked @Josh O\'Connor\'s approach where he does not use a UISearchController. This controller still (Xcode 9) has a layout bug that many are trying to workaround.

I did revert to using a UISearchBar instead of a UITextField, and it works quite nicely. My requirement for the search/filter is to produce an NSPredicate. This is passed to the FRC:

   class ViewController: UIViewController, UITableViewDelegate, 
 UITableViewDataSource, UISearchBarDelegate {

        @IBOutlet var searchBar: UISearchBar!

         func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {

                shouldShowSearchResults = true

                if let queryString = searchBar.text {
                    filterList(queryString)

                    fetchData()
                }
            }



          func filterList(_ queryString: String) {
        if (queryString == \"\") {
            searchPredicate = nil
    }
        else {
            let brandPredicate = NSPredicate(format: \"brand CONTAINS[c] %@\", queryString)
            let modelPredicate = NSPredicate(format: \"model CONTAINS[c] %@\", queryString)
            let orPredicate = NSCompoundPredicate(type: .or, subpredicates: [brandPredicate, modelPredicate])
            searchPredicate = orPredicate
    }

}

...

let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        let request = NSFetchRequest<NSFetchRequestResult>(entityName: filmEntity)
        request.returnsDistinctResults = true
        request.propertiesToFetch = [\"brand\", \"model\"]

        request.sortDescriptors = [sortDescriptor]
        request.predicate = searchPredicate

Finally, wire up the SearchBar to its delegate.

I hope this helps others

回答11:

Simple Approach to Filter existing UITableView using CoreData and which is already sorted how you want.

This literally too me 5 minutes to setup and get working.

I had an existing UITableView using CoreData populated with Data from iCloud and which has pretty complicated user interactions and I didn\'t want to have to replicate all that for a UISearchViewController. I was able to simply add a predicate to the existing FetchRequest already used by the FetchResultsController and which filters the already sorted data.

-(void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
{
    NSPredicate *filterPredicate;

    if(searchText != nil && searchText.length > 0)
        filterPredicate = [NSPredicate predicateWithFormat:@\"(someField CONTAINS[cd] %@) OR (someOtherField CONTAINS[cd] %@)\", searchText, searchText];
    else
        filterPredicate = nil;

    _fetchedResultsController.fetchRequest.predicate = filterPredicate;

    NSError *error = nil;
    [_fetchedResultsController performFetch:&error];
    [self.tableView reloadData];
}