iPhone 弹出对话框 让用户等待

- (void) performDismiss
{
    [baseAlert dismissWithClickedButtonIndex:0 animated:NO];
}

- (void) action: (UIBarButtonItem *) item
{
    baseAlert = [[[UIAlertView alloc] initWithTitle:@"Please Wait" message:nil delegate:self cancelButtonTitle:nil otherButtonTitles: nil] autorelease];
    [baseAlert show];

    // Create and add the activity indicator
    UIActivityIndicatorView *aiv = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
    aiv.center = CGPointMake(baseAlert.bounds.size.width / 2.0f, baseAlert.bounds.size.height - 40.0f);
    [aiv startAnimating];
    [baseAlert addSubview:aiv];
    [aiv release];

    // Auto dismiss after 3 seconds
    [self performSelector:@selector(performDismiss) withObject:nil afterDelay:3.0f];
}

首先，显示一个无按钮的alertView，然后添加一个UIActivityIndicatorView作为alertView的子视图

最后，通过alertView的dismissWithClickedButtonIndex:animated:取消显示alertView。

代码和显示效果都非常优雅