Question

I have a UIWebView which I’m using to display a variety of content, sometimes HTML and sometimes PDF/Powerpoint/etc (which is all seemingly handled by the same underlying control).

What I want to do is harness the underlying UIScrollView (a subview of the UIWebView) to capture the exact perspective of the scroll view and recreate the scroll position in another UIWebView, thus keeping them both in sync.

The problem that I’m having is that the zoomScale property of the UIScrollView is always 1.0 while displaying HTML content (though when displaying PDF content, zoomScale is correct).

I managed to find that the only place where I can get any inkling of the zoom scale of an HTML page is in the scrollViewDidEndZooming:withView:atScale: delegate method. I’ve found that the atScale: argument seems to provide a relative zoom scale, to what the zoom scale was before the zooming operation began. So for example when zooming in, that argument is >1, and when zooming out it is <1, and it seems to be a relative value between the two zoom scales rather than an absolute zoom scale).

What I’ve further found is that fundamentally, HTML and PDF content is handled by two different underlying views: there’s UIWebBrowserView which handles HTML content, and UIWebPDFView to handle displaying of PDFs.

So in other words, when using a UIWebPDFView, the zoomScale property of the UIScrollView is completely reliable (e.g. 1.0 for zoomed-out, 2.4 for zoomed-in, for example). On the other hand, UIWebBrowserView is much more fiddly, and when asking the UIScrollView for its zoomScale, always returns 1.0, but when receiving the delegate callback, receives a scale value that is a relative value.

So my questions are:-

1. Is this a bug? (This behaviour is seen on both iOS 4 and 5 from what I’ve seen).

2. How can I get both the zoomScale (or some other property/properties) for both HTML and PDF content, and get it in such a way that the state can be duplicated and kept in sync with another UIWebView.

I’m not beholden to using zoomScale, so I’m open to other suggestions for how the scroll state of a UIWebView can be captured and reproduced on another UIWebView.

Answer 1

When loading HTML, and UIWebBrowserView is being used, you can use

zoomScale = 1.0 / webView.scrollView.minimumZoomScale

Of course this is assuming that you can reliably ensure that the minimum zoom of your HTML page is 1.0, since some pages can alter the minimum zoom using the “viewport” meta tag.