Friday, September 21, 2012

{position:fixed} in iOS 6

I stumbled upon this oddity when upgrading to iOS 6 while working on a mobile advertising project, and it took me a better part of the day to figure out what is going on: all of a sudden an element {position:fixed} stopped working in a correct manner (which is staying put, while the page is scrolling), and started "sticking" to the scrolling page, moving out of the viewport, and then just "jumping" back to the correct location after the scrolling was finished.If you scroll this page, you will see it—hint: that's the one labeled "broken"—assuming that you have a correct device/browser combination. Mine was iPhone4 and iOS 6.0 (6.0.1-6.1.3 behaves just the same). On the original page, where I first encountered the problem, all of my elements were created dynamically using JavaScript, but at the end of the day (literally) it become clear, that the glitch is in the iOS 6 CSS implementation.Here is what happens: if you have an element {position:fixed} which has one child element {position:absolute}, the correct behavior will break, if parent element has no physical dimensions. In my case, the width of the element was omitted, and the height was set to 0px, but it breaks all the same, if they are just not specified.

Fix

Give parent element physical dimensions. Almost anything will work, including specifying, of course, width/height (duh), border (even transparent one, but at least 1px wide), or adding a child element which is not positioned absolutely.

Another fix

Applying an outline to ANYTHING on the page, fixes the bug for all elements.

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