iphone - iOS - 线程不会回到主线程

Question

我的线程有问题。当线程繁忙时，我在 2 个屏幕之间进行了几次 segue 之后。线程不会执行每一行..，当它必须返回主线程时，断点就会消失。有人可以帮我吗？

我在 View 卸载时释放线程。

谢谢，

- (void)fetchFeedDataIntoDocument
{
    NSString * labelString = [NSString stringWithFormat:@"Feed Fetcher %@", self.pageTitle];
    const char *label = [labelString UTF8String];

    self.fetchF = dispatch_queue_create(label, NULL);
    dispatch_async(self.fetchF, ^{

        NSArray *feeds = [FeedFetcher getDataForJson:self.pageTitle downloadBy:@"up"];

        NSDictionary *lastfeed;

        AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];

        NSManagedObjectContext *context = [appDelegate getManagedObjectContext];

        if ([feeds count] > 0)
        {
            lastfeed = [feeds objectAtIndex:0];

            [FeedFetcher setLastUpdateIdToCatgorie:self.pageTitle WithId:[lastfeed objectForKey:@"id"] AndPulishDate:[lastfeed objectForKey:@"publish_up"]];
        }

        for (NSDictionary *feedInfo in feeds) {
            [Feed FeedWithInfo:feedInfo InManageObject:context];
        }

        NSError *error = nil;

        [context save:&error];

        if (error){
            NSLog(@"Error save : %@", error);}

        dispatch_async(dispatch_get_main_queue(), ^{
            [self setupFetchedResultsController];
            [self.tableView reloadData];
            [self downloadImagesForFeeds:feeds];
        });

    });

Answer 1

您正在从创建它的不同线程访问 managedObjectContext。这是核心数据线程规则 #1。

您正在从应用委托(delegate)处获取 MOC。如果它是正常的 Xcode 生成的 MOC，那么它是使用线程限制并发创建的。您甚至不能用它调用 performBlock。您只能从主线程访问该 MOC。时期。其他任何事情充其量都是在玩火。

如果您想在一个单独的线程中完成所有工作，您还需要一个单独的 MOC。像这样(只是输入 - 没有编译)...

NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
moc.parentContext = appDelegate.managedObjectContext;
[moc performBlock:^{
    // Go get your remote data and whatever you want to do

    // Calling save on this MOC will push the data up into the "main" MOC
    // (though it is now in the main MOC it has not been saved to the store).
    [moc save:&error];
}];

这会转化为这样的东西......

- (void)fetchFeedDataIntoDocument
{
    NSString * labelString = [NSString stringWithFormat:@"Feed Fetcher %@", self.pageTitle];
    const char *label = [labelString UTF8String];

    AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *mainContext = [appDelegate getManagedObjectContext];
    NSManagedObjectContext *context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    context.parentContext = mainContext;
    [context performBlock:^{    
        NSArray *feeds = [FeedFetcher getDataForJson:self.pageTitle downloadBy:@"up"];

        NSDictionary *lastfeed;


        if ([feeds count] > 0)
        {
            lastfeed = [feeds objectAtIndex:0];

            [FeedFetcher setLastUpdateIdToCatgorie:self.pageTitle WithId:[lastfeed objectForKey:@"id"] AndPulishDate:[lastfeed objectForKey:@"publish_up"]];
        }

        for (NSDictionary *feedInfo in feeds) {
            [Feed FeedWithInfo:feedInfo InManageObject:context];
        }

        NSError *error = nil;

        [context save:&error];

        if (error){
            NSLog(@"Error save : %@", error);}
DO you really want to continue on error?
        dispatch_async(dispatch_get_main_queue(), ^{
            // Data has been pushed into main context from the background
            // but it still needs to be saved to store...
            // Do not forget to perform error handling...
            NSError *error = nil;
            [mainContext save:&error];
            [self setupFetchedResultsController];
            [self.tableView reloadData];
            [self downloadImagesForFeeds:feeds];
        });

    });

编辑

Xcode 生成的用于创建 MOC 的代码使用 init，它使用 NSConfinementConcurrencyType。您可以将它替换为 MainConcurrency，不会有任何问题，但会获得一些好处。

在您的应用委托(delegate)文件中，替换...

    __managedObjectContext = [[NSManagedObjectContext alloc] init];

有了这个...

    __managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];

现在，您的主 MOC 可以是“父类”，您也可以对其调用 performBlock。