iOS:JS获取WKWebView高度,无法获取WKWebVie

- (void)webView:(WKWebView*)webView didFinishNavigation:(null_unspecifiedWKNavigation*)navigation {

    [webViewevaluateJavaScript:@"Math.max(document.body.scrollHeight, document.body.offsetHeight, document.documentElement.clientHeight, document.documentElement.scrollHeight, document.documentElement.offsetHeight)"

              completionHandler:^(id_Nullableresult,NSError*_Nullableerror) {

                  if(!error) {

                      NSNumber*height = result;

                      // do with the height

                  }

              }];

}