需要有关活动指示器的帮助

Question

我无法让我的活动指示器工作。

这就是我所得到的-

-(void)viewWillAppear:(BOOL)animated{
[super viewWillAppear:YES];
//Create an instance of activity indicator view
UIActivityIndicatorView * activityIndicator = [[UIActivityIndicatorView alloc] initWithFrame:CGRectMake(0, 0, 20, 20)];
//set the initial property
[activityIndicator stopAnimating];
[activityIndicator hidesWhenStopped];
//Create an instance of Bar button item with custome view which is of activity indicator
UIBarButtonItem * barButton = [[UIBarButtonItem alloc] initWithCustomView:activityIndicator];
//Set the bar button the navigation bar
[self navigationItem].rightBarButtonItem = barButton;
//Memory clean up
[activityIndicator release];
[barButton release];
}

代码中应该启动然后结束的部分--

...
    else if ([theSelection isEqualToString: @"Update statistics"])
    {
        [self startTheAnimation];
        [updateStatistics  updateThe2010Statistics];
        [self stopTheAnimation];
    }
...


-(void)startTheAnimation {
    [(UIActivityIndicatorView *)[self navigationItem].rightBarButtonItem.customView startAnimating];
}

-(void)stopTheAnimation {
    [(UIActivityIndicatorView *)[self navigationItem].rightBarButtonItem.customView stopAnimating];
}

Answer 1

至少更改：

   [activityIndicator hidesWhenStopped];

到：

   activityIndicator.hidesWhenStopped = YES;

或删除该行，因为 YES 是默认值。

Answer 2

您很可能会阻塞系统的事件线程：您是否正在执行从某个 IBAction 回调或系统触发的任何其他方法调用 [updateStatistics updateThe2010Statistics]; 的方法（像 -viewDidLoad、-viewWillAppear 或类似的）？

在这种情况下，您的长时间运行的任务将阻塞事件线程，从而无法更新您的活动指示器。尝试执行以下操作：

...
else if ([theSelection isEqualToString: @"Update statistics"])
{
  [self startTheAnimation];
  [self performSelectorInBackground:@selector(doUpdateStatistics) withObject:nil];
}
...

- (void) doUpdateStatistics {
  [updateStatistics  updateThe2010Statistics];
  [self performSelectorOnMainThread:@selector(stopTheAnimation) withObject:nil waitUntilDone:NO];
}

这将在第二个线程上执行统计更新，以便事件线程可以正确更新活动指示器。在更新统计信息结束时，我们再次在主线程（即事件线程）上调用停止动画来停止您的活动指示器。