iPhone SDK - UIWebView has a grey box over it

Question

Sometimes, my UIWebView will have a grey box over part or all of the content. I can\'t make heads or tails of why it\'s happening. It happens regularly for certain content.

Answer 1

I've used stringByEvaluatingJavaScriptFromString plus moving UIWebView origin. Design overview: I had a set of controls(UIImage in this example) above(I mean frame.origin.y) UIWebView. So, layout was:

UIView
  UIScrollView
    UIImageView
    UIWebView

Since UIWebView doesn't support scrolling in such hierarchy I've rearrange it like:

UIView
  UIScrollView
    UIImageView
  UIWebView

My view controller is delegate for UIWebViewDelegate and UIScrollViewDelegate. Then,

- (void)viewDidLoad
{
  // set delegates
  self.scrollView.delegate = self;
  self.webView.delegate = self;

  // store original UIWebView position in ivar
  webViewPosY = self.webView.frame.origin.y;

  // load html into UIWebView
  [self.webView loadHTMLString:someHTML baseURL:nil];
}

- (void)webViewDidFinishLoad:(UIWebView *)webView
{
  // get UIWebView size and store in ivar
  webSize = [self.webView sizeThatFits:CGSizeMake(1.0,1.0)];

  // set proper content height for UIScrollView
  CGSize contentSize = self.scrollView.contentSize;
  contentSize.height = webViewPosY + webSize.height;
  self.scrollView.contentSize = contentSize; 

  // set UIWebView's frame height same as UIScrollView has
  CGRect wf = self.webView.frame;
  wf.size.height = self.scrollView.frame.size.height;
  self.webView.frame = wf;
}

// scrolling logic:
// 1.  if origin of UIWebView > 0 then move UIWebView itself
// 2.  if origin of UIWebView == 0 then scroll with javascript
// 3.  if origin is 0 and whole html is scrolled then move UIWebView again(this happens to support scroll "bouncing", or if you have some views below UIWebView
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
  CGFloat scrollPosY = self.scrollView.contentOffset.y;

  // (1) and (2) ifs
  // how much to move UIWebView
  CGFloat scrollOriginY = (scrollPosY >= webViewPosY) ? webViewPosY : scrollPosY;
  // how much to scroll via JS
  CGFloat scrollJSY = scrollPosY - scrollOriginY;

  // (3) if
  if ( scrollPosY > (webSize.height - scrollViewSize.height + webViewPosY ) )
    scrollOriginY += scrollPosY - (webSize.height - scrollViewSize.height + webViewPosY);

  // scroll with JS
  [self.webView stringByEvaluatingJavaScriptFromString:[NSString stringWithFormat:@"document.body.scrollTop = %f;", scrollJSY]];

  // move UIWebView itself
  CGRect wf = self.webView.frame;
  wf.origin.y = webViewPosY - scrollOriginY;
  self.webView.frame = wf;
}

This works just fine for me.