如何通知NSFetchedResultsController关于[NSManagedObjectContext保存]

Question

我在Objective-C中有以下问题。当我从我的ManagedObjectContext中删除一个对象并保存了这个改变时，我如何通知我的fetchedResultsController执行新的提取？根据我的理解，发送performFetch-Message方法是不正确的。

谢谢！

Answer 1

您可以使用postNotificaton为此，您应该已经在控制器中设置了一个观察器，该观察器将再次启动提取请求。使用该委托方法

Answer 2

你可以把它更多钞票

fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:[self managedObjectContext] sectionNameKeyPath:nil cacheName:nil]; 

，并设置参数cacheName到零值。它避免了崩溃和ManagedObjectContext变更后只保留最新数据

#pragma mark - 
#pragma mark Fetched results controller delegate 


- (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 *tableViews = self.tableView; 

switch(type) { 

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

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

    case NSFetchedResultsChangeUpdate: 
     [_delegate configureCell:[tableViews cellForRowAtIndexPath:indexPath] atIndexPath:indexPath]; 
     break; 

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


- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller { 
[self.tableView endUpdates]; 
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:0]; 
[self.tableView scrollToRowAtIndexPath:indexPath 
         atScrollPosition:UITableViewScrollPositionMiddle 
           animated:NO]; 
} 

这段代码自动更新并重新加载当您添加，删除或更新NSFetchedResultsController和的UITableViewController