// webview被指示加载内容时调用，返回YES才会进行加载
  - (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType;
  // webview已经开始加载一个请求后调用
  - (void)webViewDidStartLoad:(UIWebView *)webView;
  // webview结束加载请求之后调用
  - (void)webViewDidFinishLoad:(UIWebView *)webView;
  // 请求加载中发生错误时调用
  - (void)webView:(UIWebView *)webView didFailLoadWithError:(nullable NSError *)error;

 // 方法一
  NSHTTPURLResponse *response = nil;
  [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
  NSLog(@"statusCode:%ld", response.statusCode);
   // 方法二
  NSURLSessionDataTask * dataTask = [[NSURLSession sharedSession] dataTaskWithRequest:webView.request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
    NSHTTPURLResponse *tmpresponse = (NSHTTPURLResponse*)response;
    NSLog(@"statusCode:%ld", tmpresponse.statusCode);
  }];
  [dataTask resume];