我尝试使用 NSFetchedResultsController 来向我的 tableView 显示部分。但现在我的 tableView 保持为空。
@property (nonatomic,strong) NSManagedObjectContext* managedObjectContext;
@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;
- (NSManagedObjectContext *)managedObjectContext
{
NSManagedObjectContext *context = nil;
id delegate = [[UIApplication sharedApplication] delegate];
if ([delegate performSelector:@selector(managedObjectContext)]) {
context = [delegate managedObjectContext];
}
return context;
}
- (void)viewDidLoad
{
self.fetchedResultsController = nil;
self.fetchedResultsController.delegate = nil;
}
- (NSFetchedResultsController *)fetchedResultsController {
if (_fetchedResultsController != nil) {
return _fetchedResultsController;
}
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
// Create and configure a fetch request with the plant entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Travel" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
// Create the sort descriptors array.
NSSortDescriptor *nameDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:nameDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
// Create and initialize the fetch results controller.
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:@"country" cacheName:@"country"];
self.fetchedResultsController = aFetchedResultsController;
_fetchedResultsController.delegate = self;
return _fetchedResultsController;
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// Return the number of sections.
return [[self.fetchedResultsController sections] count];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
id <NSFetchedResultsSectionInfo> sectionInfo = [self.fetchedResultsController sections][section];
return [sectionInfo numberOfObjects];
}
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { return @""; }
我遵循了一个教程，但 tableView 现在是空的。我的 tableView 工作正常（使用 coreData）。也许有人知道我的问题的答案。谢谢。