NSfetchedResultsController更改不反映到UI

Question

問題NSFetchedResultsController是我提取數據，它填充UITableView與cacheName設置爲nil。稍後，當我更改NSFetchedResultsController的predicate並將其稱爲perfromFetch時，它將不會刷新UITableView，但NSFetchedResultsController中的數據已更新。還有一件事，NSFetchedResultsControllerDelegate方法也沒有調用。

在此先感謝。

編輯：添加的代碼

NSFetchedResultsControllerDelegate

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

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath { 

    UITableView *tableView = self.tableView; 

    switch(type) { 

     case NSFetchedResultsChangeUpdate: 
      [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath]; 
      [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade]; 
      break; 

     case NSFetchedResultsChangeInsert: 
      [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade]; 
      break; 

     case NSFetchedResultsChangeDelete: 
      [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; 
      break; 

     case NSFetchedResultsChangeMove: 
      [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; 
      [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade]; 
      break; 
    } 
} 

- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id)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; 

     case NSFetchedResultsChangeMove: 
     case NSFetchedResultsChangeUpdate: 
      break; 
    } 
} 

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

NSFetchedResultsController

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

    NSManagedObjectContext *context = [GmailDBService sharedService].managedObjectContext; 
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Thread"]; 
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"historyId" ascending:NO]; 
    fetchRequest.predicate = [NSPredicate predicateWithFormat:@"SUBQUERY(messages, $m, ANY $m.labels.identifier == %@).@count > 0", self.label.identifier]; 
    fetchRequest.sortDescriptors = @[sortDescriptor]; 
    fetchRequest.fetchBatchSize = 20; 

    _fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:context sectionNameKeyPath:nil cacheName:nil]; 
    _fetchedResultsController.delegate = self; 
    [_fetchedResultsController performFetch:nil]; 

    return _fetchedResultsController; 
} 

謂語刷新

- (IBAction)unwindToThreadsController:(UIStoryboardSegue *)segue 
{ 
    self.fetchedResultsController.fetchRequest.predicate = [NSPredicate predicateWithFormat:@"identifier == %@", @"15f1919682399cc9"]; 
    [self.fetchedResultsController performFetch:nil]; 
} 

Answer 1

fetchedResultsCo ntroller並不昂貴。你不應該無心創建並根據需要銷燬它們。當您需要更改謂詞時放棄當前的fetchedResultsController並創建一個新的。在這樣做之後，不要忘記重新加載tableView。

更改不會觸發fetchedResultsController，因爲您正在監視線程，但謂詞基於消息。所以當消息被改變時，它不會觸發fetchedResultsController中的更改。控制器只監視對一個實體的更改，並且不希望其他實體發生更改來影響它。你可以通過幾種方法解決這個問題：1）設置你的fetchedResultsController來查看消息並按線程分組，然後只顯示每一部分（即線程）作爲一行。 2）每次你改變一條消息也改變它的線程（message.thread.threadId = message.thread.threadId將被視爲一個改變，就fetchedResultsController而言）。

此外，fetchBatchSize不受fetchedResultsController的重視，因此爲了清晰起見您應該將其刪除。