在UIWebView中转换触摸点以保存内容

当您按住一个恰好是图像的可见元素时，我一直在尝试从UIWebView保存图像。我正在努力寻找如何将UILongPressGestureRecognizer的接触点转换为Javascript所需的点，以获得正确的位置。我认为这和webView的scrollView的内容插入有关，但我不太确定。

如果有任何帮助，我将不胜感激。

代码：

- (void)longPress:(UILongPressGestureRecognizer *)sender
{
    if (sender.state == UIGestureRecognizerStateBegan)
    {
        CGPoint pt = [sender locationInView:self.webView];
        CGPoint offset;
        offset.x = [[self.webView stringByEvaluatingJavaScriptFromString:@"window.pageXOffset"]integerValue];
        offset.y = [[self.webView stringByEvaluatingJavaScriptFromString:@"window.pageYOffset"]integerValue];
        CGSize windowSize;
        windowSize.width = [[self.webView stringByEvaluatingJavaScriptFromString:@"window.innerWidth"]integerValue];
        windowSize.height = [[self.webView stringByEvaluatingJavaScriptFromString:@"window.innerHeight"]integerValue];
        CGFloat f = windowSize.width / self.webView.frame.size.width;
        pt.x = (pt.x * f);
        pt.y = (pt.y - self.webView.scrollView.contentInset.top) * f;
        NSString *js = [NSString stringWithFormat:@"document.elementFromPoint(%f, %f).tagName", pt.x, pt.y];
        NSString *tagName = [self.webView stringByEvaluatingJavaScriptFromString:js];
        if (tagName && [tagName caseInsensitiveCompare:@"IMG"] == NSOrderedSame)
        {
            NSString *imgURL = [NSString stringWithFormat:@"document.elementFromPoint(%f, %f).src", pt.x, pt.y];
            NSString *urlToDownload = [self.webView stringByEvaluatingJavaScriptFromString:imgURL];
            NSArray *validImageTypes = @[@".jpg",@".jpeg",@".gif",@".tif",@".tiff",@".ico",@".bmp",@".bmpf",@".cur",@".xbm",@".png"];
            for (NSString *sub in validImageTypes)
            {
                if (urlToDownload.length >= sub.length)
                {
                    NSString *extension = [urlToDownload substringFromIndex:MAX(urlToDownload.length - sub.length, 0)];
                    if ([extension caseInsensitiveCompare:sub] == NSOrderedSame)
                    {
                        // Image found, proceed to download (code omitted)
                        break;
                    }
                }
            }
        }
    }
}