状态栏上的转轮实现

在看切克闹项目，有个加载网页的：

#pragma mark --

#pragma mark UIWebViewDelegate

- (void)webViewDidStartLoad:(UIWebView *)webView

{

    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;

}

- (void)webViewDidFinishLoad:(UIWebView *)webView

{

    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

}

- (void)webView:(UIWebView *)webView didFailLoadWithError:(NSError *)error

{

    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

}