显示微调器并将其在同一块中删除

在一个可能需要几秒钟的方法中，我有：

UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc]initWithFrame:CGRectMake(135,140,50,50)];
spinner.color = [UIColor blueColor];
[spinner startAnimating];
[_mapViewController.view addSubview:spinner];

// lots of code

[spinner removeFromSuperview];

旋转器没有出现。可能是因为当时屏幕没有更新。 我该如何解决这个问题？

Use GCD:

UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc]initWithFrame:CGRectMake(135,140,50,50)];
spinner.color = [UIColor blueColor];
[spinner startAnimating];
[_mapViewController.view addSubview:spinner];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // lots of code run in the background

    dispatch_async(dispatch_get_main_queue(), ^{
        // stop and remove the spinner on the main thread when done
        [spinner removeFromSuperview];
    });
});