「死磕」Core Data——非标准数据类型的保存

- (void)initializeFetchedResultsController {

    // 这里的kUserEntityName就是你在xcdatamodeld文件的实体名称。
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:kUserEntityName];
    
    // 返回数据的排序规则(最少需要有一个sort descriptor)
    // Need at least one sort descriptor
    NSSortDescriptor *nameSort = [NSSortDescriptor sortDescriptorWithKey:kUserNameKey ascending:YES];
    
    [request setSortDescriptors:@[nameSort]];
    
    // 实例化fetchedResultsController对象
    // 需要利用在此之前已经创建的NSManagedObjectContext对象
    // 最后一个参数，可以复制一个字符串，Core Data会自己设置缓存，以提升性能。
    [self setFetchedResultsController:[[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:[SPKManager shareManager].store.context sectionNameKeyPath:nil cacheName:nil]];

     // 设置委托对象
     // 协议中有4个委托方法，用来告诉UITableView，Core Data中的数据有变化
    [self.fetchedResultsController setDelegate:self];
    
    NSError *error = nil;
    if (![[self fetchedResultsController] performFetch:&error]) {
        NSLog(@"Failed to initialize FetchedResultsController: %@\n%@", [error localizedDescription], [error userInfo]);
        abort();
    }
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    
    id<NSFetchedResultsSectionInfo>sectionInfo = self.fetchedResultsController.sections[section];
    return [sectionInfo numberOfObjects];
}

SPKUser *user = [self.fetchedResultsController objectAtIndexPath:indexPath];
cell.textLabel.text = user.userName;
cell.detailTextLabel.text = [NSString stringWithFormat:@"%@", @(user.userID)];

// 如果没有自定义NSManagedObject子类，就应该类似：NSManagedObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];

#pragma mark - NSFetchedResultsControllerDelegate
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller{
    [_tableView beginUpdates];
}

- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id<NSFetchedResultsSectionInfo>)sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type {
    switch (type) {
        case NSFetchedResultsChangeInsert:
              // 插入了section
            [_tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
            
        case NSFetchedResultsChangeDelete:
              // 删除了section
            [_tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
            
        case NSFetchedResultsChangeMove:
            break;
            
        case NSFetchedResultsChangeUpdate:
            break;
            
        default:
            break;
    }
}

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
    switch (type) {
        case NSFetchedResultsChangeInsert:
            // 插入了新对象
            [_tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
            
        case NSFetchedResultsChangeDelete:
              // 删除了对象
            [_tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
            
        case NSFetchedResultsChangeUpdate:
            // 修改了对象
            [self configureCell:[_tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
            break;
            
        case NSFetchedResultsChangeMove:
              // 移动了对象 
            [_tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [_tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
            
        default:
            break;
    }
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
    [_tableView endUpdates];
}

#import "HAEqTransformer.h"
#import "HAEq.h"

// 我的自定义对象是HAEq
@implementation HAEqTransformer

+ (Class)transformedValueClass {
    return [NSData class];
}

- (id)transformedValue:(id)value {
    if (!value) {
        return nil;
    }
    
    if ([value isKindOfClass:[NSData class]]) {
        return value;
    }
    
    HAEq *eq = (HAEq *)value;
    // 将自定义对象转换成NSData
    NSData *dataFromEq = [NSKeyedArchiver archivedDataWithRootObject:eq];
    
    return dataFromEq;
}

- (id)reverseTransformedValue:(id)value {
    NSData *data = (NSData *)value;
    // 将NSData对象转换为自定义对象
    HAEq *eq = [NSKeyedUnarchiver unarchiveObjectWithData:data];
    return eq;
}
@end