我有一个由NSFetchedResultsController驱动的UITableView。 tableview有一个自定义页脚视图，我正在使用RestKit从api获取数据并将响应映射到Core Data。
在RestKit请求返回后，我遇到了一个非常奇怪的行为，其中响应被映射到核心数据，我的FetchedResultsController发送其委托（我的tableview控制器）更新，并且tableview被部分更新，全部小于1第二。然后，几秒钟后，tableview完成更新。我说tableview是部分更新的，因为最初，tablefooterview没有重绘，并且在它下面添加了单元格。直到延迟之后，页脚才会移动到位。
我尝试使用乐器分析应用程序，这似乎不是绘制/加载单元格中基于CPU的延迟。我也尝试过只在配置单元格时设置单元格的标题标签以最小化复杂性。我也在设备和模拟器上看到了相同的行为。
我真的很想追踪并消除这种延迟，因为它确实会导致糟糕的用户体验。
除了日志之外：
2012-09-18 10:39:43.695 MyApp[28881:470f] -[RDRMarketBooksViewController controllerWillChangeContent:] [Line 236] controller => <NSFetchedResultsController: 0xe657570>
2012-09-18 10:39:43.695 MyApp[28881:470f] -[RDRMarketBooksViewController controller:didChangeObject:atIndexPath:forChangeType:newIndexPath:] [Line 267] controller => <NSFetchedResultsController: 0xe657570>
(...19 similiar lines...)
2012-09-18 10:39:43.703 MyApp[28881:470f] -[RDRMarketBooksViewController controllerDidChangeContent:] [Line 301] controller => <NSFetchedResultsController: 0xe657570>
2012-09-18 10:39:43.705 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xed5f890; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xed5f9b0>>, indexPath => <NSIndexPath 0xed5eab0> 2 indexes [0, 0]
2012-09-18 10:39:43.706 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe659e50; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe659f70>>, indexPath => <NSIndexPath 0xe657b50> 2 indexes [0, 1]
2012-09-18 10:39:43.708 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe65aca0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe65adc0>>, indexPath => <NSIndexPath 0xe65a6f0> 2 indexes [0, 2]
2012-09-18 10:39:43.709 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe9e1890; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe9b1e10>>, indexPath => <NSIndexPath 0xe9c59d0> 2 indexes [0, 3]
2012-09-18 10:39:43.711 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0x13c6f230; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0x13c6ed80>>, indexPath => <NSIndexPath 0xe9e0fb0> 2 indexes [0, 4]
2012-09-18 10:39:43.712 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe9e2230; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe9b1a60>>, indexPath => <NSIndexPath 0xe9e0ea0> 2 indexes [0, 5]
2012-09-18 10:39:43.713 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0x13c6fef0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0x13c70010>>, indexPath => <NSIndexPath 0xe95dca0> 2 indexes [0, 6]
2012-09-18 10:39:43.714 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xeb599f0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xeb59b10>>, indexPath => <NSIndexPath 0xe9e2a10> 2 indexes [0, 7]
2012-09-18 10:39:43.715 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0x13c70d10; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0x13c6fea0>>, indexPath => <NSIndexPath 0xe9e1790> 2 indexes [0, 8]
2012-09-18 10:39:43.717 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xed616c0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xed5ee80>>, indexPath => <NSIndexPath 0xe9e1d50> 2 indexes [0, 9]
2012-09-18 10:39:43.718 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe65bb00; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe65b680>>, indexPath => <NSIndexPath 0xe65b1c0> 2 indexes [0, 11]
2012-09-18 10:39:43.720 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0x13c71c00; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0x13c71770>>, indexPath => <NSIndexPath 0x13c6f1d0> 2 indexes [0, 13]
2012-09-18 10:39:43.721 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe65c900; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe65c4a0>>, indexPath => <NSIndexPath 0xe659ce0> 2 indexes [0, 14]
2012-09-18 10:39:43.722 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe65d720; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe65d2c0>>, indexPath => <NSIndexPath 0xe659de0> 2 indexes [0, 15]
2012-09-18 10:39:43.723 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe65e5a0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe65e110>>, indexPath => <NSIndexPath 0xe65d2a0> 2 indexes [0, 16]
2012-09-18 10:39:43.739 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0x91bf9e0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0x9197560>>, indexPath => <NSIndexPath 0x91c9960> 2 indexes [0, 17]
2012-09-18 10:39:43.740 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0x93e8d50; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0x93dd090>>, indexPath => <NSIndexPath 0x93cb8b0> 2 indexes [0, 18]
2012-09-18 10:39:43.741 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0x13c727b0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0x13c728d0>>, indexPath => <NSIndexPath 0x13c72420> 2 indexes [0, 19]
2012-09-18 10:39:43.742 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0x93e6ff0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0x93da000>>, indexPath => <NSIndexPath 0x93d4d10> 2 indexes [0, 21]
2012-09-18 10:39:43.744 MyApp[28881:470f] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xed62510; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xed620a0>>, indexPath => <NSIndexPath 0xed5ed80> 2 indexes [0, 22]
2012-09-18 10:39:43.772 MyApp[28881:c07] -[RDRMarketBooksViewController controllerWillChangeContent:] [Line 236] controller => <NSFetchedResultsController: 0xe657570>
2012-09-18 10:39:43.777 MyApp[28881:c07] -[RDRMarketBooksViewController controller:didChangeObject:atIndexPath:forChangeType:newIndexPath:] [Line 267] controller => <NSFetchedResultsController: 0xe657570>
(...19 similiar lines...)
2012-09-18 10:39:43.788 MyApp[28881:c07] -[RDRMarketBooksViewController controllerDidChangeContent:] [Line 301] controller => <NSFetchedResultsController: 0xe657570>
2012-09-18 10:39:43.790 MyApp[28881:c07] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0x13c7be10; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0x13c7bf30>>, indexPath => <NSIndexPath 0x13c7b080> 2 indexes [0, 0]
2012-09-18 10:39:43.791 MyApp[28881:c07] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe9e2be0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe9e1b10>>, indexPath => <NSIndexPath 0xe977940> 2 indexes [0, 1]
2012-09-18 10:39:43.792 MyApp[28881:c07] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe9e38b0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe9e2190>>, indexPath => <NSIndexPath 0xe9c0bc0> 2 indexes [0, 2]
2012-09-18 10:39:43.793 MyApp[28881:c07] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0xe9e4680; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0xe9e41f0>>, indexPath => <NSIndexPath 0xe9e3d60> 2 indexes [0, 3]
2012-09-18 10:39:43.794 MyApp[28881:c07] -[RDRMarketBooksViewController configureCell:atIndexPath:] [Line 34] cell => <RDRMarketBooksCell: 0x13c7ccc0; baseClass = UITableViewCell; frame = (0 0; 320 79); autoresize = W+BM; layer = <CALayer: 0x13c7cde0>>, indexPath => <NSIndexPath 0x13c7b270> 2 indexes [0, 4]
2012-09-18 10:39:43.802 MyApp[28881:c07] -[RDRMarketBooksViewController productsDidLoad:forCategory:error:] [Line 319] resource => <RDRRangedResource: 0x9533390> => {
来自我的UITableViewController子类的相关方法：
- (void)configureCell:(RDRMarketBooksCell *)cell atIndexPath:(NSIndexPath *)indexPath {
NSParameterAssert(cell);
NSParameterAssert(indexPath);
Trace(@"cell => %@, indexPath => %@", cell, indexPath);
NSAssert([cell isKindOfClass:[RDRMarketBooksCell class]], @"should be a market books cell");
id<RDRAPIProduct> product = [fetchedResultsController objectAtIndexPath:indexPath];
cell.titleLabel.text = product.name;
}
#pragma mark -
#pragma mark UITableViewDelegate
// Configuring Rows for the Table View
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
return 79.0;
}
- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
if (!tableViewIsUpdating) {
[(RDRMarketBooksCell *)cell refreshSecondaryValues];
}
}
// Managing Selections
- (NSIndexPath *)tableView:(UITableView *)tableView willSelectRowAtIndexPath:(NSIndexPath *)indexPath {
id<RDRAPIProduct> product = [fetchedResultsController objectAtIndexPath:indexPath];
BOOL shouldSelect = YES;
if (product) {
shouldSelect = (product.slug != nil);
}
return (shouldSelect ? indexPath : nil);
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
id<RDRAPIProduct> product = [fetchedResultsController objectAtIndexPath:indexPath];
if (RDRIsiPad()) {
[[RDRApplicationDelegate sharedDelegate] presentDetailsWithProduct:product];
}
[self.delegate viewController:self didPickProduct:product];
[tableView deselectRowAtIndexPath:indexPath animated:YES];
}
#pragma mark -
#pragma mark UITableViewDataSource
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
RDRMarketBooksCell *cell = [tableView dequeueReusableCellWithIdentifier:kRDRMarketBooksCellIdentifier];
NSAssert(cell, @"cell should not be nil");
[self configureCell:cell atIndexPath:indexPath];
return cell;
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return [[fetchedResultsController sections] count];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
id <NSFetchedResultsSectionInfo> sectionInfo = [[fetchedResultsController sections] objectAtIndex:section];
return [sectionInfo numberOfObjects];
}
#pragma mark -
#pragma mark NSFetchedResultsControllerDelegate
/*
Assume self has a property 'tableView' -- as is the case for an instance of a UITableViewController
subclass -- and a method configureCell:atIndexPath: which updates the contents of a given cell
with information from a managed object at the given index path in the fetched results controller.
*/
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
Trace(@"controller => %@", controller);
if (controller == fetchedResultsController) {
tableViewIsUpdating = YES;
[self.tableView beginUpdates];
}
}
- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type {
Trace(@"controller => %@", controller);
if (controller == fetchedResultsController) {
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 {
Trace(@"controller => %@", controller);
if (controller == fetchedResultsController) {
UITableView *tableView = self.tableView;
switch(type) {
case NSFetchedResultsChangeInsert:
[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeDelete:
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeUpdate:
[tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeMove:
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
withRowAnimation:UITableViewRowAnimationFade];
[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]
withRowAnimation:UITableViewRowAnimationFade];
break;
}
}
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
Trace(@"controller => %@", controller);
if (controller == fetchedResultsController) {
[self.tableView endUpdates];
tableViewIsUpdating = NO;
// double delayInSeconds = 0.1;
// dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
// dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
// [self fetchSecondaryValues];
// });
}
}
答案 0 :(得分：1)
解决。 NSFetchedResultsController使用RKManagedObjectStore的primaryManagedObjectContext。我把它切换到mainQueueManagedObjectContext，问题就解决了。
我更仔细地查看了RestKit，mainQueueManagedObjectContext是primaryManagedObjectContext的子代（然后发现文档中提到了这个事实）。我原本以为RestKit映射出现在primaryManagedObjectContext上，但现在我的猜测是它们出现在mainQueueManagedObjectContext上，并保存在低优先级线程上，保存到primaryManagedObjectContext，然后保存到持久性存储。我的NSFetchedResultsController以前附加到primaryManagedObjectContext，这将解释结果完全出现之前的长延迟。然而，在这种情况下使用mainQueueManagedObjectContext的需要并没有在文档中显而易见。但回想起来，文档确实提到mainQueueManagedObjectContext的目的是使数据可以通过primaryManagedObjectContext写入持久存储，而不会导致UI断断续续。
我创建NSFetchedResultsController的代码现在看起来像：
NSManagedObjectContext *context = [[RKManagedObjectStore defaultStore] mainQueueManagedObjectContext];
NSFetchRequest *fr = [NSFetchRequest fetchRequestWithEntityName:@"RDRProduct"];
fr.fetchBatchSize = 20;
fr.predicate = [NSPredicate predicateWithFormat:@"ANY categories.slug == %@", category.slug];
fr.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"sortingTitle" ascending:YES]];
[NSFetchedResultsController deleteCacheWithName:category.slug];
NSFetchedResultsController *fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fr
managedObjectContext:context
sectionNameKeyPath:@"sortingSection"
cacheName:category.slug];
我的tableview现在正常运行。