实现代码

self.activityIndicatorView=[[UIActivityIndicatorView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];
    self.activityIndicatorView.center=self.view.center;
//设置样式
    [self.activityIndicatorView setActivityIndicatorViewStyle:UIActivityIndicatorViewStyleGray];
    [self.activityIndicatorView setActivityIndicatorViewStyle:UIActivityIndicatorViewStyleWhiteLarge];
    [self.activityIndicatorView setBackgroundColor:[UIColor lightGrayColor]];
    [self.view addSubview:self.activityIndicatorView];
//开始动画
    [self.activityIndicatorView startAnimating];

关于style的设置，有三种白色和灰色，这两种的尺寸都是20*20，白色大图是37*37:

typedef NS_ENUM(NSInteger, UIActivityIndicatorViewStyle) {
    UIActivityIndicatorViewStyleWhiteLarge,
    UIActivityIndicatorViewStyleWhite,
    UIActivityIndicatorViewStyleGray,
};

关闭动画

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5* NSEC_PER_SEC)), dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),^{
        [self.activityIndicatorView stopAnimating];
    });