UIActivityIndicatorView

 -(id)initWithActivityIndicatorStyle:(UIActivityIndicatorViewStyle)style;

 - (void)startAnimating;

- (void)stopAnimating;

- (BOOL)isAnimating; 

 1 // 初始化指示器
 2 UIActivityIndicatorView *indicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
 3 
 4 // 设置指示器位置
 5 indicator.center = CGPointMake(self.view.frame.size.width * 0.5, self.view.frame.size.height * 0.5);
 6 
 7 // 开启动画，必须调用，否则无法显示
 8 [indicator startAnimating];
 9 
10 [self.view addSubview:indicator];