Question

我在解决后台队列中的modalviewcontroller时遇到了问题。这是代码

- (void)cleanUpPictures
{
    dispatch_queue_t queue = dispatch_queue_create("ch.thurboapp.cleanup", NULL);
    dispatch_async(queue, ^{
        NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init];
        [context setPersistentStoreCoordinator:[self.managedObjectContext persistentStoreCoordinator]];
        //register for core data save notification
        [[NSNotificationCenter defaultCenter] addObserver:self 
                                                 selector:@selector(mergeChanges:)
                                                     name:NSManagedObjectContextDidSaveNotification
                                                   object:context];
        [self deleteAllObjects:@"Thumbnail" inContext:context];
        [self deleteAllObjects:@"MenuThumbnail" inContext:context];
        [self deleteAllObjects:@"PictureData" inContext:context];
        [context release];
        dispatch_async(dispatch_get_main_queue(), ^{
            [[NSUserDefaults standardUserDefaults] setObject:[NSDate date] forKey:LastCleaned];
            [[NSUserDefaults standardUserDefaults] synchronize];
            [self.parentViewController dismissModalViewControllerAnimated:YES];
        });
    });
    dispatch_release(queue);
}

[self.parentViewController dismissModalViewControllerAnimated:YES];

在主线程内调用，但没有效果。有人知道这个问题的解决方案吗？

非常感谢帮助。

Answer 1

我不太熟悉UI代码在块中的交互方式，但您是否尝试过更简单的performSelectorOnMainThread？

Answer 2

尝试使用调度组在第一个工作块完成时通知您：

- (void)cleanUpPictures
{
    dispatch_queue_t queue = dispatch_queue_create("ch.thurboapp.cleanup", NULL);
    // To know when we're done, we need to associate work in this queue
    // with a group
    dispatch_group_t group = dispatch_group_create();

dispatch_group_async(group, queue, ^{
    NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init];
    [context setPersistentStoreCoordinator:[self.managedObjectContext persistentStoreCoordinator]];
    //register for core data save notification
    [[NSNotificationCenter defaultCenter] addObserver:self 
                                             selector:@selector(mergeChanges:)
                                                 name:NSManagedObjectContextDidSaveNotification
                                               object:context];
    [self deleteAllObjects:@"Thumbnail" inContext:context];
    [self deleteAllObjects:@"MenuThumbnail" inContext:context];
    [self deleteAllObjects:@"PictureData" inContext:context];
    [context release];
});

// When the last block of work in this group finishes
// dispatch_group_notify fires
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        [[NSUserDefaults standardUserDefaults] setObject:[NSDate date] forKey:LastCleaned];
        [[NSUserDefaults standardUserDefaults] synchronize];
        [self.parentViewController dismissModalViewControllerAnimated:YES];
    });

dispatch_release(queue);
dispatch_release(group);
}

当排队在主队列上时，dismissModalViewController无法正常工作

2 个答案: