iPhone dev: Increase scroll speed in UIWebView?

Question

I have an app in which I render local HTML files in a UIWebView. The files, however, are sometimes large, and getting to where you want takes a long time with the default scroll speed. Is there any way to boost up the vertical scroll speed of a UIWebView?

Answer 1

In iOS 5 we can access the scrollView property of the UIWebView.

If you are targeting iOS 5+, you can simply call:

webView.scrollView.decelerationRate = UIScrollViewDecelerationRateNormal;

Answer 2

Find a subview of UIWebView which is a UIScrollView, then set decelerationRate to UIScrollViewDecelerationRateNormal. This makes the UIWebView as fast as an ordinary UIScrollView.

In iOS 4/5, we can simply use the last subview of UIWebView.

UIScrollView *scroll = [webView.subviews lastObject];
if ([scroll isKindOfClass:[UIScrollView class]]) {
    scroll.decelerationRate = UIScrollViewDecelerationRateNormal;
}

The default decelerationRate of UIWebView's UIScrollView is 0.989324, while UIScrollViewDecelerationRateFast is 0.99, and UIScrollViewDecelerationRateNormal is 0.998.

This method doesn't use any private API.

Answer 3

Search for a subview of UIWebView that responds to -setScrollDecelerationFactor: (it's UIScroller - a private class that's the only subview of UIScrollView). You'll find that it takes the same deceleration factors defined for the public UIScrollView class:

- (void)webViewDidFinishLoad:(UIWebView *)aView {
    id decelerator = [aView viewWithSelector:@selector(setScrollDecelerationFactor:)];
    [decelerator setScrollDecelerationFactor:UIScrollViewDecelerationRateNormal];
}

Note that the method I'm using viewWithSelector: is a method I defined in a category of UIView. Presumably, if UIWebView changes in future, my search will return nil and this method will become a no-op.