How to Programmatically Scroll Android WebView

Question

I'm trying to programmatically scroll a WebView to the location of a particular element in the DOM tree. But so far I haven't been able to get the WebView to respond to scroll requests. I've tried calling JavaScript that uses window.scrollTo(...), but the WebView doesn't respond. On the Java side, I've tried calling the WebView.flingScroll(...) method. WebView will respond to flingScroll, but what I need is a scrollTo(...) capability. Any ideas?

Answer 1

It turns out that the window.scrollTo() DOES work, you just can't add your own method named scrollTo(). For some reason my own scrollTo() method was being invoked when I called window.scrollTo().

So, in summary, to scroll a WebView to a particular DOM element, write a JavaScript function to do the scrolling:

function scrollToElement(id) {
    var elem = document.getElementById(id);
    var x = 0;
    var y = 0;

    while (elem != null) {
        x += elem.offsetLeft;
        y += elem.offsetTop;
        elem = elem.offsetParent;
    }
    window.scrollTo(x, y);
}

and then from your Android app (Java code), tell your WebView to load a URL:

webView.loadUrl("javascript:scrollToElement('" + elemId + "')");

There are some issues with this approach, such as the scroll will not be nicely animated, but the general mechanism works.

The DOM window object does report the current scroll position of the WebView correctly (see window.pageXOffset, window.pageYOffset or window.scrollX, window.scrollY). If you just want to know the current scroll position of the WebView, write some JavaScript to call your Java code and pass along the X/Y offsets.

Answer 2

I've found a better answer to this issue. It turns out that WebView does have scrollTo(), getScrollX() and getScrollY() methods as you'd expect. They're a bit hidden in the documentation because they're inherited from View (via AbsoluteLayout -> ViewGroup -> View). This is obviously a better way to manipulate the WebView's scroll position than the somewhat cumbersome JavaScript interface.

Answer 3

Hi Guys!

kindly explain the behavior of webView.flingScroll(vx, vy)?thanks.