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
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
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];
}