UIActivityIndicatorView的用法

 _activityView = [[UIActivityIndicatorView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];

 _activityView.center = self.view.center;

 _activityView.activityIndicatorViewStyle = UIActivityIndicatorViewStyleWhiteLarge;

 _activityView.hidesWhenStopped = YES;

 _activityView.color = [UIColor greenColor];

 [self.view addSubview:_activityView];

在需要开始的地方调用：

 [_activityView startAnimating];

在需要结束的地方调用：

[_activityView stopAnimating];