[IOS开发进阶与实战]第一天:CoreData的运行机制

1.数据模型NSManagedObjectModel的建立

1.- (NSManagedObjectModel *)managedObjectModel
{
    if (_managedObjectModel != nil) {
        return _managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"CoreDataApp" withExtension:@"momd"];//加载我们的 modeld文件 得到modelURL
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];  //获得有实体类型的Model
    return _managedObjectModel;
}

这里使用了懒加载,就是说第一次加载之后,以后就不会再次加载,除非这个模型被删除了.

然后根据我们文件中的 CoreDataApp.momd 文件名字进行加载,得到 模型的URL.

最后通过URL 就可以得到我们的 managedObjectModel.

2.持久化存储的设置(就相当于我们的所要存储地方的文件)

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{     //持久化存储控制器
    if (_persistentStoreCoordinator != nil) {
        return _persistentStoreCoordinator;
    }
    
    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"CoreDataApp.sqlite"];//app的存储位置,得到存储位置的URL
    
    NSError *error = nil;
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];//加载上面的定义好的模型
    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
        //设置存储方式,存储位置.得到定义好的 持久化存储位置
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    
    
    return _persistentStoreCoordinator;
}

首先得到我们的存储位置,制作成 URL .然后依赖于模型 制作我们的持久化管理器.

然后把我们的存储位置植入到我们的持久化管理器中.对错误进行处理 .

3.

- (NSManagedObjectContext *)managedObjectContext  
{
    if (_managedObjectContext != nil) {
        return _managedObjectContext;
    }
    
    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        _managedObjectContext = [[NSManagedObjectContext alloc] init];   //加载我们的定义好的模型和持久化存储位置,得到我们的上下文.
        [_managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return _managedObjectContext;
}

4.

4.app中断时候的保存
- (void)applicationWillTerminate:(UIApplication *)application
{
    // Saves changes in the application's managed object context before the application terminates.
    [self saveContext];
}

- (void)saveContext
{
    NSError *error = nil;
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil) {
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
             // Replace this implementation with code to handle the error appropriately.
             // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        } 
    }
}

5.

//5.按钮的添加和事件触发
- (void)insertNewObject:(id)sender
{
    NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
    NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity];
    NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];
    
    // If appropriate, configure the new managed object.
    // Normally you should use accessor methods, but using KVC here avoids the need to add a custom class to the template.
    [newManagedObject setValue:[NSDate date] forKey:@"timeStamp"];
    
    // Save the context.
    NSError *error = nil;
    if (![context save:&error]) {
         // Replace this implementation with code to handle the error appropriately.
         // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
}

//6.请求控制器的实现
- (NSFetchedResultsController *)fetchedResultsController
{
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }
    
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];//请求
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Event" inManagedObjectContext:self.managedObjectContext];//依赖上下文实体的名称
    [fetchRequest setEntity:entity]; //对请求设置具体实体的描述
    
    // Set the batch size to a suitable number.
    [fetchRequest setFetchBatchSize:20]; //每次能够取出20条记录.
    
    // Edit the sort key as appropriate.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"timeStamp" ascending:NO];//设置实体属性的key.设定排序规则  
    NSArray *sortDescriptors = @[sortDescriptor];
    
    [fetchRequest setSortDescriptors:sortDescriptors];//添加实体的属性到请求中
    
    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Master"];//创建请求控制器.
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;
    
	NSError *error = nil;
	if (![self.fetchedResultsController performFetch:&error]) {
	     // Replace this implementation with code to handle the error appropriately.
	     // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
	    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
	    abort();
	}
    
    return _fetchedResultsController;
} 

7.协议的实现

#pragma mark - Fetched results controller

- (NSFetchedResultsController *)fetchedResultsController
{
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }
    
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];//请求
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Event" inManagedObjectContext:self.managedObjectContext];//依赖上下文实体的名称
    [fetchRequest setEntity:entity]; //对请求设置具体实体的描述
    
    // Set the batch size to a suitable number.
    [fetchRequest setFetchBatchSize:20];
    
    // Edit the sort key as appropriate.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"timeStamp" ascending:NO];//设置实体的属性名称
    NSArray *sortDescriptors = @[sortDescriptor];
    
    [fetchRequest setSortDescriptors:sortDescriptors];//添加实体的属性到请求中
    
    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Master"];//创建请求控制器.
    aFetchedResultsController.delegate = self;//NSFetchedResultsControllerDelegate
    self.fetchedResultsController = aFetchedResultsController;
    
	NSError *error = nil;
	if (![self.fetchedResultsController performFetch:&error]) {
	     // Replace this implementation with code to handle the error appropriately.
	     // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
	    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
	    abort();
	}
    
    return _fetchedResultsController;
}    

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView beginUpdates];
}

- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)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)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:@[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
            
        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
            
        case NSFetchedResultsChangeUpdate:
            [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
            break;
            
        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView endUpdates];
}

/*
// Implementing the above methods to update the table view in response to individual changes may have performance implications if a large number of changes are made simultaneously. If this proves to be an issue, you can instead just implement controllerDidChangeContent: which notifies the delegate that all section and object changes have been processed. 
 
 - (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    // In the simplest, most efficient, case, reload the table view.
    [self.tableView reloadData];
}
 */

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath
{
    NSManagedObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];
    cell.textLabel.text = [[object valueForKey:@"timeStamp"] description];
}