用好NSFetchedResultsController，程序的performance能大 大提高。原因在于你用NSFetchedResultsController去读取数据的话，苹果公司那些顶尖的工程师已经帮你想好了如何最大效率地读取 数据库。 所以，干脆利落地去掉NSArray和NSMutableArray，只用NSFetchedResultsController! 1,首先在h文件加入下面这段代码。

@interfaceFailedBanksListViewController:UITableViewController{ 	NSFetchedResultsController*_fetchedResultsController; 	NSManagedObjectContext*_context; } @property(nonatomic, retain) NSFetchedResultsController*fetchedResultsController; @property(nonatomic, retain)NSManagedObjectContext*context; @end

2,在m文件中，加入下面的代码

@synthesize fetchedResultsController = _fetchedResultsController;

3，在dealloc函数中，加入下面的代码:

self.fetchedResultsController.delegate=nil; self.fetchedResultsController =nil;

4，在viewDidUnload函数中，加入下面的代码:

-(void)viewDidUnload { 	self.fetchedResultsController =nil; }

5，在m文件中，加入如下函数（以FailedBackInfo为数据对象）

-(NSFetchedResultsController*)fetchedResultsController { 	if(_fetchedResultsController !=nil){ 		return _fetchedResultsController; 	 	NSFetchRequest*fetchRequest =[[NSFetchRequest alloc] init]; 	NSEntityDescription*entity =[NSEntityDescription         entityForName:@"FailedBankInfo" inManagedObjectContext:_context]; 	[fetchRequest setEntity:entity]; 	NSSortDescriptor*sort =[[NSSortDescriptor alloc]         initWithKey:@"details.closeDate" ascending:NO]; 	[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]]; 	[fetchRequest setFetchBatchSize:20]; 	NSFetchedResultsController*theFetchedResultsController = 	[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:_context sectionNameKeyPath:nil cacheName:@"Root"]; 	self.fetchedResultsController = theFetchedResultsController;     	_fetchedResultsController.delegate=self; 	[sort release]; 	[fetchRequest release]; 	[theFetchedResultsController release]; 	return _fetchedResultsController; }

上面的代码中，entity为实体对象，_context是coredata的NSManagedObject对象，它是连接数据库的一个上下文对象，相当于一个连接器。sort用来排序。cacheName用来组织数据成sections（这样组织方便后面展示） 6，在viewDidLoad中加入下面代码：

-(void)viewDidLoad { 	[super viewDidLoad]; 	NSError*error; 	if(![[self fetchedResultsController] performFetch:&error]){ 		// Update to handle the error appropriately. 		NSLog(@"Unresolved error %@, %@", error,[error userInfo]); 		exit(-1);// Fail 	} 	self.title =@"Failed Banks"; }

7，接下来，在UITableView中显示。

-(NSInteger)tableView:(UITableView*)tableView numberOfRowsInSection:(NSInteger)section { 	id  sectionInfo = [[_fetchedResultsController sections] objectAtIndex:section]; 	return[sectionInfo numberOfObjects]; } -(void)configureCell:(UITableViewCell*)cell atIndexPath:(NSIndexPath*)indexPath { 	FailedBankInfo*info =[_fetchedResultsController objectAtIndexPath:indexPath]; 	cell.textLabel.text = info.name; 	cell.detailTextLabel.text =[NSString stringWithFormat:@"%@, %@", info.city, info.state]; } -(UITableViewCell*)tableView:(UITableView*)tableView cellForRowAtIndexPath:(NSIndexPath*)indexPath { 	staticNSString*CellIdentifier=@"Cell"; 	UITableViewCell*cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 	if(cell ==nil){         	cell =[[[UITableViewCell alloc]             initWithStyle:UITableViewCellStyleSubtitle             reuseIdentifier:CellIdentifier] autorelease]; 	} 	// Set up the cell... 	[self configureCell:cell atIndexPath:indexPath]; 	return cell; }

8,当数据发生变化时，coredata会自动通知显示层即UITableView作刷新。

-(void)controllerWillChangeContent:(NSFetchedResultsController*)controller { 	// The fetch controller is about to start sending change notifications, so prepare the table view for updates. 	[self.tableView beginUpdates]; }
-(void)controller:(NSFetchedResultsController*)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath*)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath*)newIndexPath { 	UITableView*tableView =self.tableView; 	switch(type){ 	case NSFetchedResultsChangeInsert: 		[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade]; 		break; 	case NSFetchedResultsChangeDelete: 		[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; 		break; 	case NSFetchedResultsChangeUpdate: 		[self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath]; 		break; 	case NSFetchedResultsChangeMove: 		[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; 		// Reloading the section inserts a new row and ensures that titles are updated appropriately. 		[tableView reloadSections:[NSIndexSet indexSetWithIndex:newIndexPath.section] withRowAnimation:UITableViewRowAnimationFade]; 		break; 	} }
-(void)controller:(NSFetchedResultsController*)controller didChangeSection:(id )sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type { 	switch(type){ 	case NSFetchedResultsChangeInsert: 		[self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade]; 		break; 	case NSFetchedResultsChangeDelete: 		[self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade]; 		break; 	} }
-(void)controllerDidChangeContent:(NSFetchedResultsController*)controller { 	// The fetch controller has sent all current change notifications, so tell the table view to process all updates. 	[self.tableView endUpdates]; }