ios - 显示微调器并在同一 block 中将其删除

Question

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];

微调器没有显示。可能是因为当时屏幕没有更新。我怎样才能解决这个问题？

Answer 1

使用 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];
    });
});