Question

为什么我会收到“wait_fences：未能收到回复”这段代码？这是我使用通知回传给主线程的方式吗？

#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

这里有一个明显的问题。您正在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。然后处理程序解除必须在主线程上完成的警报视图。尝试将代码更改为：

- (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：输入太快，更改了答案以反映正确的UI对象。

Answer 2

以下是摆脱wait_fences错误的方法。更改解除alertView的行以使用动画，如下所示：

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

我认为wait_fences与具有警报视图的视图动画状态有关，但很难确定。我认为这应该消除错误消息。我的另一个答案没有直接摆脱错误，但我仍然推荐它。 UI操作应该在主线程上完成。

为什么我会为此代码获得“wait_fences：未能收到回复”？

2 个答案: