类 NSFetchedResultsController详解

来源:互联网 发布:java.util.map 编辑:程序博客网 时间:2024/07/17 21:13
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];}
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