ios - 一个 FetchedResultsController 用于一个 UIViewController 中的两个 UITableView

Question

我正在使用最新的 SDK 和使用核心数据的 XCode 4.5.2 开发一个 iOS 应用。

在 UIViewController 上，我将有两个 UITableView，shopsList 和 productsList。我想使用 Core Data，这是我第一次使用它。所以，我开始使用 Xcode Master Detail 模板，我在 MasterViewController.m 上找到了这段代码:

- (NSFetchedResultsController *)fetchedResultsController
{
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Event" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    // 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];
    NSArray *sortDescriptors = @[sortDescriptor];

    [fetchRequest setSortDescriptors:sortDescriptors];

    // 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"];
    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;
}

如果我有这个 UIViewController 接口(interface):

@interface FirstViewController : UIViewController<CLLocationManagerDelegate, UITableViewDataSource, UITableViewDelegate, UISearchBarDelegate>
{
    CLLocationManager* locationManager;
    BOOL isMenuHidden;
    BOOL isShopsListOpen;
    BOOL isProductsListOpen;
    long int selectedShopRow;
    long int selectedProductRow;
    NSIndexPath* shopCheckedIndexPath;
    NSIndexPath* productCheckedIndexPath;
}

@property (unsafe_unretained, nonatomic) IBOutlet UITableView *shopsList;
@property (unsafe_unretained, nonatomic) IBOutlet UITableView *productsList;

[ ... ]

如果我有一个 shop 和一个 product NSManagedObject。

我怎样才能使 - (NSFetchedResultsController *)fetchedResultsController 适应这两个 UITableView？

我可能需要 NSFetchedResultsController，不是吗？

Answer 1

首先在应用委托(delegate)中分配 viewController 的 managedObjectContext。

@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (strong, nonatomic) NSFetchedResultsController *productsListFetchedResultsController;
@property (strong, nonatomic) NSFetchedResultsController *shopsListFetchedResultsController;

在您的数据模型中创建 2 个实体，并根据需要在 appdelegate 中填充一些可用数据。

在 viewWillAppear 中，您将 2 个实体获取到 2 个 NSFetchedResultsController，只需将基本的 fetchResult block 代码拖到实用程序面板中并将上下文更改为 self.manageObjectContext，将实体名称更改为关联名称