ios - 单击 UITableview 行后 UIActivityIndi​​catorView 不显示？

Question

点击后指示器不显示，它首先加载下一页，然后显示几毫秒。我希望它从行单击开始一直保留在那里，直到下一个屏幕完全加载。

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{

UIActivityIndicatorView *activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
activityIndicator.frame = CGRectMake(0,0,50,50);
activityIndicator.tintColor = [UIColor blackColor];
activityIndicator.center = self.view.center;
[self.view addSubview:activityIndicator];
[activityIndicator startAnimating];

UIStoryboard *sb = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
UIViewController *vc = [sb instantiateViewControllerWithIdentifier:@"6"];
vc.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
[self presentViewController:vc animated:YES completion:NULL];
}

Answer 1

尝试更改代码，以便将 UIActivityIndi​​catorView 代码放在主线程上。

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    dispatch_async(dispatch_get_main_queue(), ^{
        UIActivityIndicatorView *activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
        activityIndicator.frame = CGRectMake(0,0,50,50);
        activityIndicator.tintColor = [UIColor blackColor];
        activityIndicator.center = self.view.center;
        [self.view addSubview:activityIndicator];
        [activityIndicator startAnimating];
    });


    UIStoryboard *sb = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    UIViewController *vc = [sb instantiateViewControllerWithIdentifier:@"6"];
    vc.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
    [self presentViewController:vc animated:YES completion:NULL];
}