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当我的应用程序正在加载某些屏幕时，我有代码显示带有活动轮的“正在加载...”视图。如果加载时间特别长（例如，超过 4 秒），那么我想显示一条附加消息，上面写着“抱歉，这需要很长时间，请耐心等待！” 我这样做的方法是在 4 秒延迟上使用 NSTimer，它调用一个方法来创建一个等待视图，然后将这个新视图覆盖在加载视图上，这样单词不会重叠。如果页面加载时间少于 4 秒，则加载视图被隐藏，等待视图永远不会被触发，用户继续他或她的快乐方式。

当我测试需要超过 4 秒的屏幕加载时，我似乎无法显示额外的视图。这是我的代码：

// this method is triggered elsewhere in my code
// right before the code to start loading a screen
- (void)showActivityViewer
{     
    tooLong = YES;
    waitTimer = [NSTimer scheduledTimerWithTimeInterval:4.0
                                                   target:self
                                                 selector:@selector(createWaitAlert)
                                                 userInfo:nil
                                                  repeats:NO];
    [[NSRunLoop currentRunLoop] addTimer: waitTimer forMode: NSDefaultRunLoopMode];

    loadingView = [LoadingView createLoadingView:self.view.bounds.size.width     :self.view.bounds.size.height];    
    [self.view addSubview: loadingView];

    // this next line animates the activity wheel which is a subview of loadingView
    [[[loadingView subviews] objectAtIndex:0] startAnimating]; 
}

- (void)createWaitAlert
{
    [waitTimer invalidate];
    if (tooLong) 
    {
        UIView *waitView = [LoadingView createWaitView:self.view.bounds.size.width :self.view.bounds.size.height];
        [self.view addSubview:waitView];
    }
}

// this method gets triggered elsewhere in my code
// when the screen has finished loading and is ready to display
- (void)hideActivityViewer
{
    tooLong = NO;
    [[[loadingView subviews] objectAtIndex:0] stopAnimating];
    [loadingView removeFromSuperview];
    loadingView = nil;
}
4

1 回答 1

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你确定你是从主线程执行的吗？尝试这个：

- (void)showActivityViewer
{     
    tooLong = YES;

    dispatch_async(dispatch_queue_create(@"myQueue", NULL), ^{
        [NSThread sleepForTimeInterval:4];
        [self createWaitAlert];
    });

    loadingView = [LoadingView createLoadingView:self.view.bounds.size.width     :self.view.bounds.size.height];    
    [self.view addSubview: loadingView];

    // this next line animates the activity wheel which is a subview of loadingView
    [[[loadingView subviews] objectAtIndex:0] startAnimating]; 
}

- (void)createWaitAlert
{
    dispatch_async(dispatch_get_main_queue(), ^{
        if (tooLong) 
        {
            UIView *waitView = [LoadingView createWaitView:self.view.bounds.size.width :self.view.bounds.size.height];
            [self.view addSubview:waitView];
        }
    });
}
于 2012-09-21T12:12:10.003 回答