我有一个或多或少基本的 UITableViewController
和一个 NSFetchedResultsController
。 UITableViewController
被推送到 navigationController 的
堆栈上。但是推送动画并不流畅,因为 NSFetchedResultsController
的获取是在主线程上执行的,因此会阻塞 UI。
我的问题是:如何在后台线程中执行 NSFetchedResultsController
的提取以保持动画流畅?
NSFetchedResultsController
和委托(delegate)方法如下所示:
- (NSFetchedResultsController *)fetchedResultsController
{
if (_fetchedResultsController != nil) {
return _fetchedResultsController;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:@"GPGrade" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
// Set the batch size to a suitable number.
[fetchRequest setFetchBatchSize:20];
//Set predicate
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"parent == %@", self.subject];
[fetchRequest setPredicate:predicate];
// Edit the sort key as appropriate.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
NSArray *sortDescriptors = @[sortDescriptor];
[fetchRequest setSortDescriptors:sortDescriptors];
// Edit the section name key path and cache name if appropriate.
// nil for section name key path means "no sections".
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"SubjectMaster"];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return _fetchedResultsController;
}
- (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 *tableView = self.tableView;
switch(type) {
case NSFetchedResultsChangeInsert:
[tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationTop];
break;
case NSFetchedResultsChangeDelete:
[tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationRight];
break;
case NSFetchedResultsChangeUpdate:
//[self configureCell:(GPSubjectOverviewListCell *)[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
break;
case NSFetchedResultsChangeMove:
[tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
[tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
break;
}
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
[self.tableView endUpdates];
}
最佳答案
长话短说;没有充分的理由在主队列上使用上下文。
can use NSFetchedResultsController to fetch data in background
当然。 NSFetchedResultsController
可以与私有(private)队列上下文一起使用。事实上,这样做是非常快乐和高效的。 There is a bug这可以防止 NSFetchedResultsController
在使用私有(private)队列时使用它的缓存,但是缓存并没有像在 iOS 3.0 中那样赢得你的青睐。将 cacheName
设置为 nil 就可以了。
1.
使用 NSPrivateQueueConcurrencyType
创建上下文。最好不是您用于 IO 的那个。
2.
使用该上下文和缓存名称 nil 创建获取的结果 Controller 。
3.
从 performBlock:
block 中执行初始提取:
[[[self fetchedResultsController] managedObjectContext] performBlock:^{
NSError *fetchError = nil;
if (![self fetchedResultsController] performFetch:&error]){
/// handle the error. Don't just log it.
} else {
// Update the view from the main queue.
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
[tableView reloadData];
}];
}
}];
4.
您的所有委托(delegate)回调现在都将从上下文的队列中发生。如果您使用它们来更新 View ,请像上面看到的那样通过分派(dispatch)到主队列来执行此操作。
5.
...
6.
利润!
您可以阅读更多相关信息 here .
关于ios - NSFetchedResultsController:在后台线程中获取,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/14803205/