PROVISIO DevBlog

Smooth animations on Android

SiteKiosk for Android offers secured browsing preventing any misuse that could mess up your tablet configuration. But it's not only browsing that you can secure with SiteKiosk, also self service applications like for example menus, info terminals or customer surveys can be (and should be ;) run with SiteKiosk. An additonal advantage: you can use the powerful SiteKiosk Object Model to have even more control as normally possible with HTML pages. As I mentioned in an earlier post you can have access to local files via the sk:// protocol for example. We are adding more and more useful functionality to the Object Model in the future, so watch out for new versions. You can also post a comment here stating what you'd like to have us added to the SK Object Model.

Speaking of self service applications we realized early in our development process that android tablets are capable of many things, but still not comparable to desktop computers. Especially the browser component is a difficult story, since on one hand it supports many HTML5 features already (which is fantastic), but on the other hand still has some problems concerning completeness and performance of these new features. So you have to be a bit careful if you program web applications targeting android devices.

One example would be animations. Ever since JavaScript was introduced to the browser world, it has been used to program animations for web pages. Still it is widely used for that purpose on many pages and doing it quite well at least on desktop computers. Concerning Android, doing animations (like transitions) in JavaScript is not the best thing to do (even for desktop computer, but goes unnoticed most of the time). Say you want to create a sliding animation of a particular div containg some content that need to be exchanged when the user pressed a "next" button. You could use JavaScript's setInterval() and periodically update the div's left parameter. Unfortunately this results in poor results since the animation can be jerky on many Android tablets. A better way to do it is using CSS transforms and transitions. These will be hardware-accelerated even on Android tablets and therefore a lot smoother than JavaScript animations. 

An example would be:

<div style="-webkit-transform: translate(-600px, 0px); width=600px">Your content.</div>

This moves the div 600 pixel to the left relative to its normal position. Nice, but still no animation, right? Here you go:

<div style="-webkit-transition-duration: 500ms; -webkit-transform: translate(-600px, 0px); width=600px">Your content.</div>

Adding the "-webkit-transform-duration" will result in transition animations every time you change the "-webkit-transform" value. Obviously the transition will take 500 ms in this case. So Adding these two style properties results in a sliding animation moving the div from right to left by 600 pixels. There are a bunch of other transforms you can use for transitions like rotation, scaling and skewing. You could also use transitions for normal CSS style properties like "margin-left", but these might not be hardware-accelerated, so be aware.

Manipulation these style properties in JavaScript is not a big deal, but can be a bit cumbersome. My adivce is to use the free Move.js which makes adding these transitions dynamically very easy.