react-native/docs/Animations.md

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Fluid, meaningful animations are essential to the mobile user experience. Animation APIs for React Native are currently under heavy development, the recommendations in this article are intended to be up to date with the current best-practices.

requestAnimationFrame

requestAnimationFrame is a polyfill from the browser that you might be familiar with. It accepts a function as its only argument and calls that function before the next repaint. It is an essential building block for animations that underlies all of the JavaScript-based animation APIs.

JavaScript-based Animation APIs

These APIs do all of the calculations in JavaScript, then send over updated properties to the native side on each frame.

react-tween-state

react-tween-state is a minimal library that does exactly what its name suggests: it tweens a value in a component's state, starting at a from value and ending at a to value. This means that it generates the values in between those two values, and it sets the state on every requestAnimationFrame with the intermediary value.

Tweening definition from Wikipedia

"... tweening is the process of generating intermediate frames between two images to give the appearance that the first image evolves smoothly into the second image. [Tweens] are the drawings between the key frames which help to create the illusion of motion."

The most obvious way to animate from one value to another is linearly: you subtract the end value from the start value and divide the result by the number of frames over which the animation occurs, and then add that value to the current value on each frame until the end value is reached. Linear easing often looks awkward and unnatural, so react-tween-state provides a selection of popular easing functions that can be applied to make your animations more pleasing.

This library does not ship with React Native - in order to use it on your project, you will need to install it with npm i react-tween-state --save from your project directory.

var tweenState = require('react-tween-state');

var App = React.createClass({
  mixins: [tweenState.Mixin],

  getInitialState() {
    return { opacity: 1 }
  },

  _animateOpacity() {
    this.tweenState('opacity', {
      easing: tweenState.easingTypes.easeOutQuint,
      duration: 1000,
      endValue: this.state.opacity === 0.2 ? 1 : 0.2,
    });
  },

  render() {
    return (
      <View style={{flex: 1, justifyContent: 'center', alignItems: 'center'}}>
        <TouchableWithoutFeedback onPress={this._animateOpacity}>
          <View ref={component => this._box = component}
                style={{width: 200, height: 200, backgroundColor: 'red',
                        opacity: this.getTweeningValue('opacity')}} />
        </TouchableWithoutFeedback>
      </View>
    )
  },
});

Run this example

Here we animated the opacity, but as you might guess, we can animate any numeric value. Read more about react-tween-state in its README.

Rebound

Rebound.js is a JavaScript port of Rebound for Android. It is similar in concept to react-tween-state: you have an initial value and set an end value, then Rebound generates intermediate values that you can use for your animation. Rebound is modeled after spring physics; we don't provide a duration when animating with springs, it is calculated for us depending on the spring tension, friction, current value and end value. Rebound is used internally by React Native on Navigator and WarningBox.

Notice that Rebound animations can be interrupted - if you release in the middle of a press, it will animate back from the current state to the original value.

var rebound = require('rebound');

var App = React.createClass({
  // First we initialize the spring and add a listener, which calls
  // setState whenever it updates
  componentWillMount() {
    // Initialize the spring that will drive animations
    this.springSystem = new rebound.SpringSystem();
    this._scrollSpring = this.springSystem.createSpring();
    var springConfig = this._scrollSpring.getSpringConfig();
    springConfig.tension = 230;
    springConfig.friction = 10;

    this._scrollSpring.addListener({
      onSpringUpdate: () => {
        this.setState({scale: this._scrollSpring.getCurrentValue()});
      },
    });

    // Initialize the spring value at 1
    this._scrollSpring.setCurrentValue(1);
  },

  _onPressIn() {
    this._scrollSpring.setEndValue(0.5);
  },

  _onPressOut() {
    this._scrollSpring.setEndValue(1);
  },

  render: function() {
    var imageStyle = {
      width: 250,
      height: 200,
      transform: [{scaleX: this.state.scale}, {scaleY: this.state.scale}],
    };

    var imageUri = "https://facebook.github.io/react-native/img/ReboundExample.png";

    return (
      <View style={styles.container}>
        <TouchableWithoutFeedback onPressIn={this._onPressIn}
                                  onPressOut={this._onPressOut}>
          <Image source={{uri: imageUri}} style={imageStyle} />
        </TouchableWithoutFeedback>
      </View>
    );
  }
});

Run this example

You can also clamp the spring values so that they don't overshoot and oscillate around the end value. In the above example, we would add this._scrollSpring.setOvershootClampingEnabled(true) to change this. See the below gif for an example of where in your interface you might use this.

Screenshot from react-native-scrollable-tab-view. You can run a simlar example here.

A sidenote about setNativeProps

As mentioned in the Direction Manipulation section, setNativeProps allows us to modify properties of native-backed components (components that are actually backed by native views, unlike composite components) directly, without having to setState and re-render the component hierarchy.

We could use this in the Rebound example to update the scale - this might be helpful if the component that we are updating is deeply nested and hasn't been optimized with shouldComponentUpdate.

// Outside of our React component
var precomputeStyle = require('precomputeStyle');

// Back inside of the App component, replace the scrollSpring listener
// in componentWillMount with this:
this._scrollSpring.addListener({
  onSpringUpdate: () => {
    if (!this._photo) { return }
    var v = this._scrollSpring.getCurrentValue();
    var newProps = precomputeStyle({transform: [{scaleX: v}, {scaleY: v}]});
    this._photo.setNativeProps(newProps);
  },
});

// Lastly, we update the render function to no longer pass in the
// transform via style (avoid clashes when re-rendering) and to set the
// photo ref
render: function() {
  return (
    <View style={styles.container}>
      <TouchableWithoutFeedback onPressIn={this._onPressIn} onPressOut={this._onPressOut}>
        <Image ref={component => this._photo = component}
               source={{uri: "https://facebook.github.io/react-native/img/ReboundExample.png"}}
               style={{width: 250, height: 200}} />
      </TouchableWithoutFeedback>
    </View>
  );
}

Run this example

It would not make sense to use setNativeProps with react-tween-state because the updated tween values are set on the state automatically by the library - Rebound on the other hand gives us an updated value for each frame with the onSpringUpdate function.

If you find your animations with dropping frames (performing below 60 frames per second), look into using setNativeProps or shouldComponentUpdate to optimize them. You may also want to defer any computationally intensive work until after animations are complete, using the InteractionManager. You can monitor the frame rate by using the In-App Developer Menu "FPS Monitor" tool.

Navigator Scene Transitions

As mentioned in the Navigator Comparison, Navigator is implemented in JavaScript and NavigatorIOS is a wrapper around native functionality provided by UINavigationController, so these scene transitions apply only to Navigator. In order to re-create the various animations provided by UINavigationController and also make them customizable, React Native exposes a NavigatorSceneConfigs API.

var SCREEN_WIDTH = require('Dimensions').get('window').width;
var BaseConfig = Navigator.SceneConfigs.FloatFromRight;

var CustomLeftToRightGesture = Object.assign({}, BaseConfig.gestures.pop, {
  // Make it snap back really quickly after canceling pop
  snapVelocity: 8,

  // Make it so we can drag anywhere on the screen
  edgeHitWidth: SCREEN_WIDTH,
});

var CustomSceneConfig = Object.assign({}, BaseConfig, {
  // A very tighly wound spring will make this transition fast
  springTension: 100,
  springFriction: 1,

  // Use our custom gesture defined above
  gestures: {
    pop: CustomLeftToRightGesture,
  }
});

Run this example

For further information about customizing scene transitions, read the source.

Native-based Animation APIs

LayoutAnimation

LayoutAnimation allows you to globally configure create and update animations that will be used for all views in the next render cycle.

var App = React.createClass({
  componentWillMount() {
    // Animate creation
    LayoutAnimation.configureNext(LayoutAnimation.Presets.spring);
  },

  getInitialState() {
    return { w: 100, h: 100 }
  },

  _onPress() {
    // Animate the update
    LayoutAnimation.configureNext(LayoutAnimation.Presets.spring);
    this.setState({w: this.state.w + 15, h: this.state.h + 15})
  },

  render: function() {
    return (
      <View style={styles.container}>
        <View style={[styles.box, {width: this.state.w, height: this.state.h}]} />
        <TouchableOpacity onPress={this._onPress}>
          <View style={styles.button}>
            <Text style={styles.buttonText}>Press me!</Text>
          </View>
        </TouchableOpacity>
      </View>
    );
  }
});

Run this example

This example uses a preset value, you can customize the animations as you need, see LayoutAnimation.js for more information.

AnimationExperimental (Deprecated)

As the name would suggest, this was only ever an experimental API and it is not recommended to use this on your apps. It has some rough edges and is not under active development. It is built on top of CoreAnimation explicit animations.

If you choose to use it anyways, here is what you need to know:

• You will need to include RCTAnimationExperimental.xcodeproj and add libRCTAnimationExperimental.a to Build Phases.
• Suited only for static "fire and forget" animations - not continuous gestures.
• Hit detection will not work as expected because animations occur on the presentation layer.

var AnimationExperimental = require('AnimationExperimental');

var App = React.createClass({
  componentDidMount() {
    AnimationExperimental.startAnimation(
      {
        node: this._box,
        duration: 1000,
        easing: 'easeInOutBack',
        property: 'scaleXY',
        toValue: { x: 1, y: 1 },
      },
    );
  },

  render() {
    return (
      <View style={{flex: 1, justifyContent: 'center', alignItems: 'center'}}>
        <View ref={component => this._box = component}
              style={{width: 200, height: 200, backgroundColor: 'red'}} />
      </View>
    )
  },
});

Now to demonstrate a known issue, and one of the reasons why it is recommended not to use AnimationExperimental currently, let's try to animate opacity from 1 to 0.5:

AnimationExperimental.startAnimation(
  {
    node: this._box,
    duration: 1000,
    easing: 'easeInOutBack',
    property: 'opacity',
    fromValue: 1,
    toValue: 0.5,
  },
);

Pop (Unsupported, not recommended)

Facebook Pop "supports spring and decay dynamic animations, making it useful for building realistic, physics-based interactions."

This is not officially supported or recommended because the direction is to move towards JavaScript-driven animations, but if you must use it, you can find the code to integrate with React Native here. Please do not open questions specific to Pop on the React Native issues, StackOverflow is a better place to answer those questions as it is not considered to be part of the core.