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React Native: Animated

ReactEurope 2015, Paris - Spencer Ahrens - Facebook

Fluid Interactions

People expect smooth, delightful experiences
Complex interactions are hard
Common patterns can be optimized

Declarative Interactions

Wire up inputs (events) to outputs (props) + transforms (springs, easing, etc.)
Arbitrary code can define/update this config
Config can be serialized -> native/main thread
No refs or lifecycle to worry about

var { Animated } = require('react-native');

New library soon to be released for React Native
100% JS implementation -> X-Platform
Per-platform native optimizations planned
This talk -> usage examples, not implementation

Gratuitous Animation Demo App

Layout uses flexWrap: 'wrap'
longPress -> drag to reorder
Tap to open example sets

Gratuitous Animation Codez

Step 1: 2D tracking pan gesture
Step 2: Simple pop-out spring on select
Step 3: Animate grid reordering with LayoutAnimation
Step 4: Opening animation

Animation Example Set

Animated.Value this.props.open passed in from parent
interpolate works with string "shapes," e.g. 'rgb(0, 0, 255)', '45deg'
Examples easily composed as separate components
Dismissing tracks interpolated gesture
Custom release logic

Tilting Photo

Pan -> translateX * 2, rotate, opacity (via tracking)
Gesture release triggers separate animations
addListener for async, arbitrary logic on animation progress
interpolate easily creates parallax and other effects

Bobbles

Static positions defined
Listens to events to maybe change selection
Springs previous selection back
New selection tracks selector
getTranslateTransform adds convenience

Chained

Classic "Chat Heads" animation
Each sticker tracks the one before it with a soft spring
decay maintains gesture velocity, followed by spring to home
stopAnimation provides the last value for setOffset

Scrolling

Animated.event can track all sorts of stuff
Multi-part ranges and extrapolation options
Transforms decompose into ordered components

React Native: Animated

Landing soon in master (days)
GitHub: @vjeux, @sahrens
Questions?