更改SegmentedControl上的NSFetchedResultsController更改

Question

我有一个UITableView，它使用核心数据NSFetchedResultsController填充。我现在在视图中添加了UISegmentedControl，当您更改当前的细分时，我希望tableview的内容发生变化。

我已经在网上阅读过，明智地使用两个不同的NSFetchedResultsControllers，因为那时我可以从内置缓存中受益。唯一的问题是，我似乎无法找到任何示例代码来做这件事，也不知道从哪里开始。

任何人都可以解释从哪里开始创建第二个NSFetchedResultsController并根据分段控件更改tableview的哪些源？

视野头代码：

#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; 

View实现代码：

@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; 
} 

任何帮助深表感谢。谢谢。

更新：更新的代码

视野头代码：

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

View实现代码：

@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

您可以添加一个表示当前选择的NSFetchedResultsController另一个实例变量。当UISegmentedControl更新更新这个伊娃。

这可能是由段

- (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]; 
    } 
} 

一个UITableViewDataSource方法为例的valuechange事件触发的动作：

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

，你必须确保只有当前nsfrc触发NSFetchedResultsControllerDelegate方法中的tableview更新。所以你也必须改变他们所有人。

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

---

编辑：不，你做错了。 currentFetchedResultsController只是一个ivar，没有延迟的加载getter。它只是一个指向当前使用的控制器的指针。

但其他两个fetchedResultsControllers应该有这样一个懒加载getter。

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

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

然后转用：

self.currentFetchedResultsController = self.keyphraseFetchedResultsController; 

或

self.currentFetchedResultsController = self.competitorFetchedResultsController;