ios - 未为 API 监听器调用 NSFetchedResultsController 委托(delegate)

Question

如果代码将委托(delegate)分配给 NSFetchedResultsController，如下所示:

-(id)initWithFetchedResultsController:(NSFetchedResultsController*)fetchedResultsController
{
    self = [super init];
    if (self != nil)
    {
        fetchedResultsController.delegate = self;
        _fetchedResultController = fetchedResultsController;
    }
    return self;
}

NSFetchedResultsControllerDelegate 方法 – controller:didChangeObject:atIndexPath:forChangeType:newIndexPath: 从未在 self 上调用:

-(void)controller:(NSFetchedResultsController *)controller
  didChangeObject:(id)anObject
      atIndexPath:(NSIndexPath *)indexPath
    forChangeType:(NSFetchedResultsChangeType)type
     newIndexPath:(NSIndexPath *)newIndexPath
{
    NSLog(@"Delegate method called"); // Never called
}

predicate没有问题，一个predicate赋值，直接用notifications工作就可以了。

Answer 1

问题是初始的 - (BOOL)performFetch:(NSError **)error 永远不会被调用，因为这个特定的代码只关心结果集的变化，而不是初始集。然而，随之而来的是 Controller 不会注意到它从未有过的数据的变化。如下更改 init 方法可解决问题:

-(id)initWithFetchedResultsController:(NSFetchedResultsController*)fetchedResultsController
{
    self = [super init];
    if (self != nil)
    {
        fetchedResultsController.delegate = self;
        _fetchedResultController = fetchedResultsController;
        [fetchedResultsController performFetch:nil];
    }
    return self;
}