Question

我在主线程上显示UIAlertView时遇到问题。尽管我在主线程上运行，但我不确定为什么会一直崩溃。下面的块在后台线程上，但我在main上有警报，如下所示：

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发表评论，一切都很好。但是对于警报，我不断收到EXC_BAD_ACCESS错误。有人可以解释一下原因吗？它是在正确的线程上，我不能让我的生活了解内存问题可能来自哪里！

Answer 1

在完成后台队列之前，可能是视图正在释放。所以，为了安全起见，你为什么不这样使用它呢;

...........
  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];
            }
        });
}).

Answer 2

这是您呈现提醒视图的方式：

UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"<#(NSString *)#>" message:@"<#(NSString *)#>" delegate:self cancelButtonTitle:@"<#(NSString *)#>" otherButtonTitles:nil];
    [alert show];
    [alert release];

Answer 3

为什么不使用目标C调用而不是使用dispatch_async：

[self performSelectorOnMainThread

您可能必须使用自己的方法将其打包。或者，使用以下方式调用它：

[self performSelector:@selector(myAlertMethod) withObject:nil afterDelay:0.25]

从第1天开始，这些方法就已经尝试过了。

主队列崩溃时UIAlertView。

3 个答案: