Your First Animation

In this section, we'll guide you through the basic concepts of Reanimated. If you're new to Reanimated, you're in the right hands! We're going to start by building a simple animation which will help you develop a basic understanding of the library. Then, in the following sections, we're going to build on top of this knowledge and further expand your skills. Let's go!

Using an Animated component

Let's start by having something that we could see on the screen. First, to create an animatable component you need to import an Animated object:

import Animated from "react-native-reanimated";

This Animated object wraps React Native built-ins such as View, ScrollView or FlatList.

You use these components as any other JSX components:

import Animated from "react-native-reanimated";

export default function App() {
  return (
    <Animated.View
      style={{
        width: 100,
        height: 100,
        backgroundColor: "violet",
      }}
    />
  );
}

info

You can create your own custom Animated components with createAnimatedComponent.

Defining a shared value

A shared value is a driving factor of all your animations. You can think of it as a React state which is automagically kept in sync between the “JavaScript” and the “native” side of your app (hence the name). You create shared values using a useSharedValue hook:

import { useSharedValue } from 'react-native-reanimated';

As with any other React hook, you need to define it in your component's body. In a shared value, you can store any JS value like number, string or boolean but also data structures such as array and object.

For now, let's use 100 as the default value of the useSharedValue hook and pass the returned value as an inline style of the Animated.View:

import Animated, { useSharedValue } from "react-native-reanimated";

export default function App() {
  const width = useSharedValue(100);

  return (
    <Animated.View
      style={{
        width,
        height: 100,
        backgroundColor: "violet",
      }}
    />
  );
}

Using a shared value

Let's create a very simple animation that will animate a width of an element. We'll make it expand by 50px on each button press. We can do this by modifying a shared value connected to the width property of an Animated.View component. I know it might sound complicated, but it's actually quite simple.

Values stored in shared values are accessed and modified by their .value property.

There's no setter or anything - you simply mutate the .value property like there's no tomorrow.

Let's define a handlePress function inside of which we'll modify the shared value:

import { Button, View } from "react-native";
import Animated, { useSharedValue } from "react-native-reanimated";

export default function App() {
  const width = useSharedValue(100);

  const handlePress = () => {
    width.value = width.value + 50;
  };

  return (
    <View style={{ flex: 1, alignItems: "center" }}>
      <Animated.View
        style={{
          width,
          height: 100,
          backgroundColor: "violet",
        }}
      />
      <Button onPress={handlePress} title="Click me" />
    </View>
  );
}

Please hold on a second before you shorten width.value = width.value + 50 to width.value += 50. We're preparing this code for the final step which will finally bring our animation to life!

caution

It's a common mistake to modify a shared value directly like this: sv = sv + 100;. Always remember to access the shared value by using the .value property instead. Here, the correct usage would be sv.value = sv.value + 100;.

Using an animation function

Finally, import withSpring function and wrap around width.value + 50 in the handlePress function so that the value which withSpring returns modifies the shared value. This will create a bouncy spring animation that transitions the width of the element from its current value (here width.value) to the new one (here width.value + 50).

import { Button, View } from "react-native";
import Animated, { useSharedValue, withSpring } from "react-native-reanimated";

export default function App() {
  const width = useSharedValue(100);

  const handlePress = () => {
    width.value = withSpring(width.value + 50);
  };

  return (
    <View style={{ flex: 1, alignItems: "center" }}>
      <Animated.View
        style={{
          width,
          height: 100,
          backgroundColor: "violet",
        }}
      />
      <Button onPress={handlePress} title="Click me" />
    </View>
  );
}

And voilà, we've made our first animation using Reanimated! You can see how it works in its full glory in a preview below:

Summary

In this section, we gained a firm grasp on the Reanimated fundamentals. We learned about Animated components, shared values and how to use them to create a simple animation. To sum up:

• Animated components are used to define animatable elements.
• Shared values are a driving factor of all animations and we define them using a useSharedValue hook.
• Shared values are always accessed and modified by their .value property (eg. sv.value = 100;).
• To create smooth animations modify shared values using animation functions like withTiming