Cambiar NSFetchedResultsController en SegmentedControl change

Question

Tengo un UITableView que se completa con un Core Data NSFetchedResultsController. Ahora agregué un UISegmentedControl a la vista y cuando cambias el segmento actual, me gustaría que el contenido de la tabla cambiara.

He leído en línea que sería aconsejable usar dos NSFetchedResultsControllers diferentes, ya que puedo aprovechar el almacenamiento en caché integrado. El único problema es que parece que no puedo encontrar ningún código de muestra para hacer esto y no sé por dónde empezar.

¿Alguien puede explicar por dónde empezar creando un segundo NSFetchedResultsController y cambiando las fuentes de la tabla basada en el control segmentado?

Ver código de cabecera:

#import <CoreData/CoreData.h> 

@interface DomainViewController : UIViewController <NSFetchedResultsControllerDelegate, UITableViewDataSource, UITableViewDelegate> { 

    UITableView *domainView; 
    UISegmentedControl *segmentedControl; 
    NSString *domain; 

} 

@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController; 
@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext; 
@property (nonatomic, retain) NSString *domain; 

@property (nonatomic, retain) IBOutlet UITableView *domainView; 
@property (nonatomic, retain) IBOutlet UISegmentedControl *segmentedControl; 

- (IBAction)segmentedControlIndexChanged; 

Ver código de implementación:

@interface DomainViewController() 
- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath; 
@end 

@implementation DomainViewController 

@synthesize fetchedResultsController = __fetchedResultsController; 
@synthesize managedObjectContext = __managedObjectContext; 
@synthesize domain; 
@synthesize domainView; 
@synthesize segmentedControl; 

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 

    if (self.managedObjectContext == nil) 
    { 
     self.managedObjectContext = [(GARankingsAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; 
    } 

} 

- (IBAction)segmentedControlIndexChanged 
{ 
    switch(self.segmentedControl.selectedSegmentIndex){ 
     case 0: 
      break; 
     case 1: 
      break; 
     default: 
      break; 
    } 
} 

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath 
{ 
    NSManagedObject *managedObject = [self.fetchedResultsController objectAtIndexPath:indexPath]; 
    cell.textLabel.text = [[managedObject valueForKey:@"Keyphrase"] description]; 
} 

#pragma mark - Table view data source 

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView 
{ 
    return [[self.fetchedResultsController sections] count]; 
} 

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section 
{ 
    id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section]; 
    return [sectionInfo numberOfObjects]; 
} 

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    static NSString *CellIdentifier = @"Cell"; 

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 
    if (cell == nil) { 
     cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; 
    } 

    // Configure the cell. 
    [self configureCell:cell atIndexPath:indexPath]; 
    return cell; 
} 

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

    /* 
    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 *entity = [NSEntityDescription entityForName:@"Result" inManagedObjectContext:self.managedObjectContext]; 
    [fetchRequest setEntity:entity]; 

    // Set the batch size to a suitable number. 
    [fetchRequest setFetchBatchSize:20]; 

    // Edit the sort key as appropriate. 
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"Keyphrase" ascending:NO]; 
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; 

    [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:@"Root"]; 
    aFetchedResultsController.delegate = self; 
    self.fetchedResultsController = aFetchedResultsController; 

    [aFetchedResultsController release]; 
    [fetchRequest release]; 
    [sortDescriptor release]; 
    [sortDescriptors release]; 

    NSError *error = nil; 
    if (![self.fetchedResultsController 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 __fetchedResultsController; 
} 

Cualquier ayuda es muy apreciada. Gracias.

ACTUALIZACIÓN: código actualizado

Ver código de cabecera:

@property (nonatomic, retain) NSFetchedResultsController *currentFetchedResultsController; 
@property (nonatomic, retain) NSFetchedResultsController *competitorFetchedResultsController; 
@property (nonatomic, retain) NSFetchedResultsController *keyphraseFetchedResultsController; 

Ver código de implementación:

@synthesize currentFetchedResultsController = __fetchedResultsController; 
@synthesize competitorFetchedResultsController; 
@synthesize keyphraseFetchedResultsController; 

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

    /* 
    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 *entity = [NSEntityDescription entityForName:@"Result" inManagedObjectContext:self.managedObjectContext]; 
    [fetchRequest setEntity:entity]; 

    // Set the batch size to a suitable number. 
    [fetchRequest setFetchBatchSize:20]; 

    // Edit the sort key as appropriate. 
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"Keyphrase" ascending:NO]; 
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; 

    [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:@"Root"]; 
    aFetchedResultsController.delegate = self; 
    //self.fetchedResultsController = aFetchedResultsController; 
    self.currentFetchedResultsController = aFetchedResultsController; 

    [aFetchedResultsController release]; 
    [fetchRequest release]; 
    [sortDescriptor release]; 
    [sortDescriptors release]; 

    NSError *error = nil; 
    //if (![self.fetchedResultsController performFetch:&error]) 
    if (![self.currentFetchedResultsController 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 __fetchedResultsController; 
} 

Answer 1

Se podría añadir otra variable de instancia que representa el NSFetchedResultsController seleccionado en ese momento. Y cuando los cambios de UISegmentedControl actualizan este ivar.

esto podría ser la acción que se desencadena por el evento valuechange del segmento

- (IBAction *)segmentChanged:(UISegmentedControl *)sender { 
    if ([sender selectedSegmentIndex] == 0) { 
     self.currentFetchedResultsController = self.nsfrc1; 
     [self.tableView reloadData]; 
    } 
    else if ([sender selectedSegmentIndex] == 1) { 
     self.currentFetchedResultsController = self.nsfrc2;  
     [self.tableView reloadData]; 
    } 
} 

un método UITableViewDataSource como ejemplo:

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { 
    return [[self.currentFetchedResultsController sections] count]; 
} 

y usted tiene que asegurarse de que sólo el nsfrc actual desencadena una actualización de tabla de vista en los métodos NSFetchedResultsControllerDelegate. Entonces debes cambiarlos a todos.

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller { 
    if (controller == self.currentFetchedResultsController) { 
     [self.tableView beginUpdates]; 
    } 
} 

---

EDIT: No, lo estás haciendo mal. el controlador CurrentFetchedResults es solo un ivar, sin un getter de carga diferida. Es "solo" un puntero al controlador actualmente utilizado.

Pero los otros dos fetchedResultsControllers deberían tener un getter de carga tan vago.

- (NSFetchedResultsController *)competitorFetchedResultsController { 
    if (!myCompetitorFetchedResultsController) { 
     // create competitorFetchedResultsController 
    } 
    return myCompetitorFetchedResultsController; 
} 

- (NSFetchedResultsController *)keyphraseFetchedResultsController { 
    if (!myKeyphraseFetchedResultsController) { 
     // create keyphraseFetchedResultsController 
    } 
    return myKeyphraseFetchedResultsController; 
} 

y luego cambiar con:

self.currentFetchedResultsController = self.keyphraseFetchedResultsController; 

o

self.currentFetchedResultsController = self.competitorFetchedResultsController;