iphone - UIAlertView在主队列上崩溃。

我在主线程上显示UIAlertView时遇到问题。我不确定为什么，但是尽管我在主线程上运行，它仍然崩溃。以下块位于后台线程上，但主要警告如下：

void (^removeFromCalendar)(NSString *, NSString *, EKEventStore *) = ^(NSString *error, NSString *eventKey, EKEventStore *eventDB) {
    EKEvent *myEvent = [eventDB eventWithIdentifier:eventKey];
    NSError *err = noErr;

    if(myEvent != NULL && myEvent != (id)[NSNull null]) {
        [eventDB removeEvent:myEvent span:EKSpanThisEvent error:&err];
    } else {

        // Event was not found, nothing to do
        return;
    }

    [eventDB release];

    if (!err || err == noErr) {
        NSLog(@"Deleted event %@", myEvent.title);

        // Show alert on the main thread
        dispatch_async(dispatch_get_main_queue(), ^{
            // Showing the alert for unattending
            NSString *resultString = @"This event was removed from your calendar.";
            UIAlertView *alert = [[[UIAlertView alloc] initWithTitle:@"Info" message:resultString delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil] autorelease];
            [alert show];
        });

        return;
    }

    error = err.description;
};

如果我在显示警报的底部注释掉，一切都很好。但是对于警报，我一直收到EXC_BAD_ACCESS错误。有人可以解释为什么吗？它在正确的线程上，我终生无法理解内存问题的根源！

最佳答案

您可能会在完成背景队列之前完成视图的释放。因此，为了安全起见，为什么不这样使用它？

...........
  UIViewController __weak *myController = self;
 dispathch_async(backgroundQueue, ^{
   UIViewController __strong *myStrongController = myController;
 ...............
 dispatch_async(dispatch_get_main_queue(), ^{
            if(myStrongController){
            // Showing the alert for unattending
            NSString *resultString = @"This event was removed from your calendar.";
            UIAlertView *alert = [[[UIAlertView alloc] initWithTitle:@"Info" message:resultString delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil] autorelease];
            [alert show];
            }
        });
}).