为什么我得到这个代码的“wait_fences：未能收到回复”？

Question

为什么我得到这个代码的“wait_fences：无法接收回复”？这是我使用通知返回主线程的方式吗？

#import "ViewController.h" 

@implementation ViewController 

@synthesize alert; 


#pragma mark - Background Thread Test Methods 

- (void) ConfigTasksForBackground:(id)sender{ 
    NSLog(@"ConfigTasksForBackground - Starting"); 
    [NSThread sleepForTimeInterval:6]; 
    [[NSNotificationCenter defaultCenter] postNotificationName:@"ModelChanged" object:self]; 
    NSLog(@"ConfigTasksForBackground - Ending"); 
} 

#pragma mark - Callbacks 

- (void) ModelChangedHandler:(NSNotification *) notification { 
    if ([[notification name] isEqualToString:@"ModelChanged"]) { 
     NSLog(@"ModelChangedHandler"); 
     [self.alert dismissWithClickedButtonIndex:0 animated:false]; 
    } 
} 

#pragma mark - View lifecycle 

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    [[NSNotificationCenter defaultCenter] addObserver:self 
              selector:@selector(ModelChangedHandler:) 
               name:@"ModelChanged" 
               object:nil]; 
} 

- (void)viewDidAppear:(BOOL)animated 
{ 
    [super viewDidAppear:animated]; 

    self.alert = [[[UIAlertView alloc] initWithTitle:@"Title" 
                message:@"viewDidAppear" 
                delegate:nil 
              cancelButtonTitle:nil 
              otherButtonTitles:nil] autorelease]; 
    [alert show]; 
    [self performSelectorInBackground:@selector(ConfigTasksForBackground:) withObject:nil]; 
} 



@end 

输出是：

2011-11-07 15:15:42.730 test_background[6876:13603] ConfigTasksForBackground - Starting 
2011-11-07 15:15:48.734 test_background[6876:13603] ModelChangedHandler 
2011-11-07 15:15:49.236 test_background[6876:13603] ConfigTasksForBackground - Ending 
wait_fences: failed to receive reply: 10004003 

Answer 1

下面是如何摆脱wait_fences错误。更改，您驳回alertView如下使用动画线：

[self.alert dismissWithClickedButtonIndex:0 animated:YES]; 

我觉得wait_fences事做，可欣赏动画状态与警惕的观点，但很难知道。我认为这应该消除错误味精虽然。我的其他答案不直接摆脱错误，但我仍然建议。 UI操作应该在主线程上完成。

Answer 2

这里有一个明显的问题。你从后台线程发布通知（这很好），这意味着在后台线程上调用通知处理程序ModelChangedHandler。处理程序然后解除必须在主线程上完成的警报视图。尝试将您的代码更改为：

- (void) ModelChangedHandler:(NSNotification *) notification { 
    if (![NSThread isMainThread]) { 
     [self performSelectorOnMainThread:@selector(ModelChangedHandler:) withObject:notification waitUntilDone:NO]; 
    } 

    else if ([[notification name] isEqualToString:@"ModelChanged"]) { 
     NSLog(@"ModelChangedHandler"); 
     [self.alert dismissWithClickedButtonIndex:0 animated:false]; 
    } 
} 

编辑：键入得太快，更改了答案以反映正确的UI对象。