例1：
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 =[NSEntityDescriptionentityForName:@"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:UITableViewCellStyleSubtitlereuseIdentifier: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];
}
例2：
在CoreData为UITableView提供数据的时候，使用NSFetchedReslutsController能提高体验，因为用NSFetchedReslutsController去读数据的话，能最大效率的读取数据库，也方便数据变化后更新界面，
具体使用方法如下：
1.添加属性
@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;
@synthesize fetchedResultsController = _fetchedResultsController;
2. 重载- (NSFetchedResultsController *)fetchedResultsController初始化NSFetchedResultsController
- (NSFetchedResultsController *)fetchedResultsController {
if (_fetchedResultsController != nil) {
return _fetchedResultsController;
}
self.fetchedResultsController = [[CoreDataManager getInstance] contactFetchedResultsController];
self.fetchedResultsController.delegate = self;
return _fetchedResultsController;
}
其中
- (NSFetchedResultsController *)contactFetchedResultsController {
BSHLOG(@"contactFetchedResultsController");
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
NSEntityDescription *entity = [NSEntityDescription entityForName:kCoreDataEntityContacts
inManagedObjectContext:self.managedObjectContext];
[request setEntity:entity];
NSSortDescriptor *recordsort = [NSSortDescriptor sortDescriptorWithKey:@"name"
ascending:NO];
[request setSortDescriptors:[NSArray arrayWithObjects:recordsort, nil]];
NSFetchedResultsController *controller = [[NSFetchedResultsController alloc] initWithFetchRequest:request
managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil
cacheName:nil];
return [controller autorelease];
}
注意：初始化NSFetchedResultsController 的时候，NSFetchRequest必须设置NSSortDescriptor
3. 在viewDidLoad中为NSFetchedResultsController获取值
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view from its nib.
self.titleNavigationItem.title = NSLocalizedString(@"contacts_title", nil);
[self fetchContacts];
}
- (void)fetchContacts {
NSError *error;
if (![self.fetchedResultsController performFetch:&error]) {
// Update to handle the error appropriately.
BSHLOG(@"[fetchSinaFriend] Unresolved error %@, %@", error, [error userInfo]);
//exit(-1); // Fail
}
}
4.在viewDidUnload和dealloc中释放
- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
[self releaseUI];
}
- (void)dealloc {
[self releaseUI];
[super dealloc];
}
- (void)releaseUI {
self.tableView = nil;
self.titleNavigationItem = nil;
self.fetchedResultsController.delegate = nil;
self.fetchedResultsController = nil;
}
5.显示在UITableView中
#pragma mark - UITableViewDataSource
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
id<NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
int count = [sectionInfo numberOfObjects];
BSHLOG(@"numberOfRowsInSection count = %d", count);
return count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
NSString *reuseIdentifier = @"ContactsViewController";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:reuseIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:reuseIdentifier];
}
EntityContacts *contact = [self.fetchedResultsController objectAtIndexPath:indexPath];
cell.textLabel.text = contact.name;
return cell;
}
6.添加NSFetchedResultsControllerDelegate的方法，当数据发生变化时，自动刷新UITableView
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
[_tableView beginUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller
didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath
forChangeType:(NSFetchedResultsChangeType)type
newIndexPath:(NSIndexPath *)newIndexPath {
switch(type) {
case NSFetchedResultsChangeInsert:{
[_tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
}
break;
case NSFetchedResultsChangeDelete:
[_tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationBottom];
break;
case NSFetchedResultsChangeUpdate:
[_tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeMove:
[_tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationBottom];
[_tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationTop];
break;
}
}
- (void)controller:(NSFetchedResultsController *)controller
didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
atIndex:(NSUInteger)sectionIndex
forChangeType:(NSFetchedResultsChangeType)type {
switch(type) {
case NSFetchedResultsChangeInsert:
[_tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationTop];
break;
case NSFetchedResultsChangeDelete:
[_tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationBottom];
break;
}
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[_tableView endUpdates];
}