Question

How would one get the contentOffset or similar information about a UIScrollView while the user is still scrolling? For example if I wanted to place an image as a header right above the content of a UIWebView, without the image being part of the WebView’s scrollView, but have it update while the user scrolls, not just jumping to the position after they let go. How could I go about doing this?

Answer 1

In iOS 5, the UIWebView has a scrollView property which is the UIScrollView responsible for handling the scrolling. Prior to iOS 5 you can search the UIWebView‘s subviews property for the subview using [subview isKindOfClass:[UIScrollView class]].

Once you have the UIScrollView, you can then set its delegate property. In the delegate you can then respond to the scrollViewDidScroll: message when the user scrolls, and update the position/contents of your header view.

Added: 29/2/2012 – In order to preserve the UIWebView‘s functionality, you will need to forward your intercepted UIScrollViewDelegate methods to the UIWebView too. To do this, you can call the UIWebView at the end of all mandatory methods within the protocol and implement something like forwardInvocation: or forwardingTargetForSelector for the optional protocol methods. This will preserve your original UIWebView behavior and allow you to enhance it with your own logic.