Question

当我尝试运行此代码时，我收到EXEC_BAD_ACCESS错误，并且用户未允许访问日历。 requestAccessToEntityType是否在单独的线程上运行，如果是这样的话，我如何访问主线程以显示UIAlertView？

EKEventStore *store = [[EKEventStore alloc] init];
if ([store respondsToSelector:@selector(requestAccessToEntityType:completion:)])
{
    [store requestAccessToEntityType:EKEntityTypeEvent completion:^(BOOL granted, NSError *error)
     {
         if ( granted )
         {
             [self readEvents];
         }
         else
         {
             UIAlertView *alert = [[UIAlertView alloc] 
                                      initWithTitle:@"Denied Access To Calendar" 
                                      message:@"Access was denied to the calendar, please go into settings and allow this app access to the calendar!" 
                                      delegate:nil 
                                      cancelButtonTitle:@"Ok" 
                                      otherButtonTitles:nil, 
                                      nil];
             [alert show];
         }
     }];
}

Answer 1

根据docs for requestAccessToEntityType

当用户点击授予或拒绝访问时，完成处理程序将在任意队列上调用。

所以，是的，它可能在与UI不同的线程上。您只能从主GUI线程中发出警报。

查看performSelectorOnMainThread。更多信息请访问：Perform UI Changes on main thread using dispatch_async or performSelectorOnMainThread?

Answer 2

您的应用程序崩溃的原因是因为您尝试处理GUI元素，即后台线程中的UIAlertView，您需要在主线程上运行它或尝试使用调度队列

使用Dispatch Queues

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);

    dispatch_async(queue, ^{

     //show your UIAlertView here... or any GUI stuff

    });

或者你可以像这样在主线程上显示GUI元素

[alertView performSelectorOnMainThread:@selector(show) withObject:nil waitUntilDone:YES];

您可以在此link

上了解有关在线程上使用GUI元素的更多详细信息

BAD ACCESS使用requestAccessToEntityType时出错

2 个答案: