coredata 最简单例子
先按照网上的教程，建一个简单的带coredata的项目再 添加一个 UserInfo 对象（表）（按照网上的教材，可视化方式添加）然后在AppDelegate.m中按如下修改，（只添加了4个方法）然后运行，看控制台日志- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{ self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; // Override point for customization after application launch. self.window.backgroundColor = [UIColor whiteColor]; [self.window makeKeyAndVisible]; [self addUser]; [self gainDatas]; return YES;}//添加-(void)addUser{ UserInfo * userInfo = [NSEntityDescription insertNewObjectForEntityForName:@"UserInfo" inManagedObjectContext:self.managedObjectContext]; userInfo.name = @"dage"; userInfo.password = @"password3"; NSError *error = nil; if (![self.managedObjectContext save:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } NSLog(@"add success"); }//查询-(void)gainDatas { NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; [fetchRequest setEntity:[NSEntityDescription entityForName:@"UserInfo" inManagedObjectContext:self.managedObjectContext]]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name like[cd]'baobao'"];//查询条件 // NSPredicate *predicate = [NSPredicate predicateWithFormat:@"password='password3'"];//查询条件 NSMutableArray *sortDescriptors = [NSMutableArray array]; //排序用 [sortDescriptors addObject:[[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES] ]; //排序用 [fetchRequest setPredicate:predicate]; //查询条件 [fetchRequest setFetchBatchSize:5]; //分页 [fetchRequest setSortDescriptors:sortDescriptors]; //排序 [fetchRequest setReturnsObjectsAsFaults:NO]; [fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:@"name", @"password", nil]]; //查询的字段，一般不需要 NSError *error = nil; NSArray *fetchedItems = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error]; if (fetchedItems == nil) { NSLog(@"fetch request resulted in an error %@, %@", error, [error userInfo]); }else { NSLog(@"fetchedItems=%d",fetchedItems.count); for (UserInfo *user in fetchedItems) { NSLog(@"user.authour=%@",user.name); // [self deleteUser:user]; //删除 // [self updateUser:user]; //更新 } } }//删除：NSManagedObject对象必须先取出来，用managedObjectContext删除，保存就好-(void)deleteUser:(id)user{ [self.managedObjectContext deleteObject:user]; NSError *error = nil; if (![self.managedObjectContext save:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } NSLog(@"delete success"); }//更新：直接修改对象，保存managedObjectContext就好-(void)updateUser:(UserInfo*)user{ user.name = @"baobao"; //修改后，直接保存managedObjectContext就可以了 NSError *error = nil; if (![self.managedObjectContext save:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } NSLog(@"update success"); }