- (void)viewDidLoad
{
    [super viewDidLoad];
    
    //创建UIActivityIndicatorView并设置样式:WhiteLarge为37 * 37,Gray和White为20 * 20
    _activityIndicatorView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
    //设置对象的位置，大小是固定不变的
    _activityIndicatorView.frame = CGRectMake(160, 230, 0, 0);
    //设置活动指示器的颜色
    _activityIndicatorView.color = [UIColor grayColor];
    
    //hidesWhenStopped默认为YES，会隐藏活动指示器。要改为NO
    //_activityIndicatorView.hidesWhenStopped = NO;
    
    //添加到当前视图
    [self.view addSubview:_activityIndicatorView];
 
    //开始动画
    [_activityIndicatorView startAnimating];
    
    //5秒之后停止动画
    [NSTimer scheduledTimerWithTimeInterval:5.0 target:self selector:@selector(stop) userInfo:nil repeats:NO];
}

- (void)stop{
    [_activityIndicatorView  stopAnimating];
}