Android WebView can't goBack from a page with iframes (Shallow Thoughts)

Akkana's Musings on Open Source Computing, Science, and Nature.

Sat, 21 Apr 2012

Android WebView can't goBack from a page with iframes

I've been fighting a bug in Android's WebView class for ages: on some pages, clicking FeedViewer's back arrow (which calls WebView::goBack()) doesn't go back to the previous page. Instead, it jumps to some random position in the current page. If you repeat it, eventually, after five or so tries (depending on the page), eventually goBack() will finally work and you'll be back at the previous page.

It was especially frustrating in that it didn't happen everywhere -- only in pages from certain sites. I saw it all the time in pages from the Los Angeles Times and from Make Magazine, but only rarely on other sites.

But I finally tracked it down: it's because those pages include the HTML <iframe> tag. Apparently, if a WebView is on a page (at least if it's a local page) that contains N iframes, the first N calls to goBack will jump somewhere in the document -- probably the location of the associated iframe, though I haven't verified that -- and only on the N+1st call will the WebView actually go back to the previous page.

The oddest thing is, this doesn't seem to be reported anywhere. Android's bug tracker finds nothing for webview iframe goback, and web searching hasn't found a hint of it, even though I see this in Android versions from 1.6 through 2.3.5. How is it possible that other people haven't noticed this? I wonder if it only happens on local file:// URLs, and not many people use those.

In any case, I'm very happy to have found the answer at last. It was easy enough to modify FeedMe to omit iframes (and who wants iframes in simplified HTML anyway?), and it's great to have a Back button that works on any page.

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[ 19:56 Apr 21, 2012    More programming | permalink to this entry | comments ]
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