loading效果

UIActivityIndicatorView *indicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];

    

    // Adjust the indicator so it is up a few pixels from the bottom of the alert    

    indicator.center = CGPointMake(alert.bounds.size.width/2,  alert.bounds.size.height-40.0);

    [indicator startAnimating];

    [alert insertSubview:indicator atIndex:1];

    [indicator release];