子视图呈现延迟

Question

在我的UITableViewController子类中，我想准备表格数据并在视图已经出现后重新加载表格（因此表格最初加载为空）。在我的应用程序委托中，我有方法来生成和删除活动屏幕。我的问题似乎是活动视图呈现被延迟到reloadData调用完成之后。我通过删除hideActivity行证明了这一点，并且确实我的活动视图与重新加载表同时出现。这里的viewDidAppear为我的视图控制器...

- (void)viewDidAppear:(BOOL)animated 
{ 
    [super viewDidAppear:animated]; 
    [(AppDelegate *)[[UIApplication sharedApplication] delegate] showActivity]; 
    [self prepare]; 
    [self.tableView reloadData]; 
    [(AppDelegate *)[[UIApplication sharedApplication] delegate] hideActivity]; 
} 

我假设这可能与没有重绘中期方法的意见去做，但在此之前不记得这种情况的发生。有任何想法吗？

...虽然我知道他们的工作，这是我的活动方法。也许我这样做的方式允许某种延迟的外观...

- (void)showActivity 
{ 
    self.activityView = [[UIView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, 480.0f)]; 
    self.activityView.backgroundColor = [[UIColor blackColor] colorWithAlphaComponent:0.75f]; 

    UIActivityIndicatorView *spinner = [[[UIActivityIndicatorView alloc] initWithFrame:CGRectMake((320.0f/2.0f) - (37.0f/2.0f), (480.0f/2.0f) - (37.0f/2.0f) - (20.0f/2.0f), 37.0f, 37.0f)] autorelease]; 
    spinner.activityIndicatorViewStyle = UIActivityIndicatorViewStyleWhiteLarge; 
    [spinner startAnimating]; 

    UILabel *label = [[[UILabel alloc] initWithFrame:CGRectMake(0.0f, spinner.frame.origin.y + spinner.frame.size.height + 10.0f, 320.0f, 30.0f)] autorelease]; 
    label.textAlignment = UITextAlignmentCenter; 
    label.text = @"Working"; 
    label.textColor = [UIColor whiteColor]; 
    label.backgroundColor = [UIColor clearColor]; 

    [self.activityView addSubview:label]; 
    [self.activityView addSubview:spinner]; 

    [self.window addSubview:self.activityView]; 
} 

- (void)hideActivity 
{ 
    [self.activityView removeFromSuperview]; 
    [self.activityView release]; 
} 

Answer 1

您的用户界面不会更新，直到您将控制权归还给runloop。您需要在后台线程中执行数据准备，或者在开始准备之前将控制返回到runloop以更新UI，如下所示：

- (void)viewDidAppear:(BOOL)animated { 
    [super viewDidAppear:animated]; 
    [(AppDelegate *)[[UIApplication sharedApplication] delegate] showActivity]; 
    [self performSelector:@selector(prepareData) withObject:nil afterDelay:0.0]; 
} 

- (void)prepareData { 
    [self prepare]; 
    [self.tableView reloadData]; 
    [(AppDelegate *)[[UIApplication sharedApplication] delegate] hideActivity]; 
}