ios - 应用卡在 dispatch_async 中

Question

这是我的代码:

        LoadViewController *loadingViewController = [[LoadViewController alloc] initWithNibName:@"LoadViewController" bundle:nil];
[self.view addSubview:loadingViewController.view];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) , ^{
    [Util deleteAllObjects:@"Unit"];
    for (NSDictionary *eachUnit in serviceData) {
        //insert in DB
        AppDelegate* appDelegate = [AppDelegate sharedAppDelegate];
        NSManagedObjectContext *context = appDelegate.managedObjectContext;
        Unit *unit = [NSEntityDescription insertNewObjectForEntityForName:@"Unit" inManagedObjectContext:context];

        unit.id_unidade = [eachUnit objectForKey:@"id"];
        unit.title = [eachUnit objectForKey:@"title"];
        unit.image = [eachUnit objectForKey:@"image"];
        unit.address = [eachUnit objectForKey:@"address"];
        unit.desc = [eachUnit objectForKey:@"desc"];
        unit.coord = [eachUnit objectForKey:@"coord"];

        NSError *error;

        if (![context save:&error]) {
            NSLog(@"Ops,fail: %@", [error localizedDescription]);
        }
    }
    NSLog(@"before");
    [self fillUnits];
    NSLog(@"after");

    dispatch_async(dispatch_get_main_queue(), ^(void) {
        NSLog(@"reload");
        [self.tableView reloadData];
        [loadingViewController.view removeFromSuperview];
        NSLog(@"after reload");

    });
});

它显示到 NSLog(@"after")，但永远不会显示到 NSLog(@"reload")。有什么线索吗？？

Answer 1

在完成处理程序中，您需要确保发送到托管对象或托管对象上下文的所有方法都使用 performBlock: 在各自的执行上下文上执行或 performBlockAndWait::

    NSManagedObjectContext *context = appDelegate.managedObjectContext;
    [context performBlockAndWait:^{
        Unit *unit = [NSEntityDescription insertNewObjectForEntityForName:@"Unit"  inManagedObjectContext:context];

        unit.id_unidade = [eachUnit objectForKey:@"id"];
        unit.title = [eachUnit objectForKey:@"title"];
        unit.image = [eachUnit objectForKey:@"image"];
        unit.address = [eachUnit objectForKey:@"address"];
        unit.desc = [eachUnit objectForKey:@"desc"];
        unit.coord = [eachUnit objectForKey:@"coord"];

        NSError *error;
        if (![context save:&error]) {
            NSLog(@"Ops,fail: %@", [error localizedDescription]);
        }
    }];

如果您的托管对象将在主线程中访问，则执行上下文必须等于主线程。

您可以在 Apple 文档中阅读更多信息:NSManagedObjectContext Reference ，尤其是“并发”一章。