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Add gestures

Gestures are a great way to provide an intuitive user experience in an app. The React Native Gesture Handler library provides built-in native components that can handle gestures. It uses the platform's native touch handling system to recognize pan, tap, rotation, and other gestures.
In this chapter, we are going to add two different gestures using the React Native Gesture Handler library:
  • Double tap to scale the size of the emoji sticker.
  • Pan to move the emoji sticker around the screen so that the user can place the sticker anywhere on the image.

Step 1: Install and configure libraries

The React Native Gesture Handler library provides a way to interact with the native platform's gesture response system. To animate between gesture states, we will use the Reanimated library.
To install them, stop the development server by pressing Ctrl + c and run the following command in the terminal:
Terminal
→ npx expo install react-native-gesture-handler react-native-reanimated
Next, also install @babel/plugin-proposal-export-namespace-from, which is required to configure the Reanimated library:
Terminal
→ npm install -D @babel/plugin-proposal-export-namespace-from
Then, add Reanimated's Babel plugin to babel.config.js:
babel.config.js
module.exports = function (api) {
  api.cache(true);
  return {
    presets: ['babel-preset-expo'],
    plugins: [
      "@babel/plugin-proposal-export-namespace-from",
      "react-native-reanimated/plugin",
    ],
  };
};
Now, start the development server again:
Terminal
→ npx expo start -c
Info-icon
Tip: We are using -c option here because we modified the babel.config.js file.
To get gesture interactions to work in the app, we'll render <GestureHandlerRootView> from react-native-gesture-handler to wrap the top-level component of our app (also known as the "root component").
To accomplish this, replace the root level <View> component in the App.js with <GestureHandlerRootView>.
App.js
import { GestureHandlerRootView } from "react-native-gesture-handler";

export default function App() {
  return (     
    <GestureHandlerRootView style={styles.container}>      
    /* ...rest of the code remains */
    </GestureHandlerRootView>
  )  
}

Step 2: Create animated components

Open the EmojiSticker.js file in the components directory. Inside it, import Animated from the react-native-reanimated library to create animated components.
EmojiSticker.js
import Animated from 'react-native-reanimated';
To make a double tap gesture work, we will apply animations to the <Image> component by passing it as an argument to the Animated.createAnimatedComponent() method.
EmojiSticker.js
// after import statements, add the following line

const AnimatedImage = Animated.createAnimatedComponent(Image);
The createAnimatedComponent() can wrap any component. It looks at the style prop of the component, determines which value is animated, and then applies updates to create an animation.
Replace the <Image> component with <AnimatedImage>.
EmojiSticker.js
export default function EmojiSticker({ imageSize, stickerSource }) {
  return (
    <View style={{ top: -350 }}>
      <AnimatedImage
        source={stickerSource}
        resizeMode="contain"
        style={{ width: imageSize, height: imageSize }}
      />
    </View>
  );
}

Step 3: Add a tap gesture

React Native Gesture Handler allows us to add behavior when it detects touch input, like a double tap event.
In the EmojiSticker.js file, import TapGestureHandler from react-native-gesture-handler and the hooks below from react-native-reanimated. These hooks will animate the style on the <AnimatedImage> component for the sticker when the tap gesture is recognized.
EmojiSticker.js
import { TapGestureHandler } from 'react-native-gesture-handler';
import Animated, {
  useAnimatedStyle,
  useSharedValue,
  useAnimatedGestureHandler,
  withSpring,
} from 'react-native-reanimated';
Inside the <EmojiSticker> component, create a reference called scaleImage using the useSharedValue() hook. It will take the value of imageSize as its initial value.
EmojiSticker.js
const scaleImage = useSharedValue(imageSize);
Creating a shared value using the useSharedValue() hook has many advantages. It helps to mutate a piece of data and allows running animations based on the current value. A shared value can be accessed and modified using the .value property. It will scale the initial value of scaleImage so that when a user double-taps the sticker, it scales to twice its original size. To do this, we will create a function and call it onDoubleTap(), and this function will use the useAnimatedGestureHandler() hook to animate the transition while scaling the sticker image.
Create the following function in the <EmojiSticker> component:
EmojiSticker.js
const onDoubleTap = useAnimatedGestureHandler({
  onActive: () => {
    if (scaleImage.value) {
      scaleImage.value = scaleImage.value * 2;
    }
  },
});
To animate the transition, let's use a spring-based animation. This will make it feel alive because it's based on the real-world physics of a spring. We will use the withSpring() hook provided by react-native-reanimated.
The useAnimatedStyle() hook from react-native-reanimated is used to create a style object that will be applied to the sticker image. It will update styles using the shared values when the animation happens. In this case, we are scaling the size of the image, which is done by manipulating the width and height properties. The initial values of these properties are set to imageSize. Create an imageStyle variable and add it to the EmojiSticker component:
EmojiSticker.js
const imageStyle = useAnimatedStyle(() => {
  return {
    width: withSpring(scaleImage.value),
    height: withSpring(scaleImage.value),
  };
});
Next, wrap the <AnimatedImage> component that displays the sticker on the screen with the <TapGestureHandler> component.
Handling tap gesture
export default function EmojiSticker({ imageSize, stickerSource }) {
  // ...rest of the code remains same
  return (
    <View style={{ top: -350 }}>
      <TapGestureHandler onGestureEvent={onDoubleTap} numberOfTaps={2}>
        <AnimatedImage
          source={stickerSource}
          resizeMode="contain"
          style={[imageStyle, { width: imageSize, height: imageSize }]}
        />
      </TapGestureHandler>
    </View>
  );
}
In the above snippet, the onGestureEvent prop takes the value of the onDoubleTap() function and triggers it when a user taps the sticker image. The numberOfTaps prop determines how many taps are required.
Let's take a look at our app on iOS, Android and the web:
Info-icon
For a complete reference on the tap gesture API, refer to the React Native Gesture Handler documentation.

Step 4: Add a pan gesture

A pan gesture allows recognizing a dragging gesture and tracking its movement. We will use this gesture handler to drag the sticker across the image.
In the EmojiSticker.js, import PanGestureHandler from the react-native-gesture-handler library.
EmojiSticker.js
import { PanGestureHandler, TapGestureHandler} from "react-native-gesture-handler";
Create an <AnimatedView> component using the Animated.createAnimatedComponent() method. Then use it to wrap the <TapGestureHandler> component by replacing the <View> component.
EmojiSticker.js
// ...rest of the code remains same
const AnimatedView = Animated.createAnimatedComponent(View);

export default function EmojiSticker({ imageSize, stickerSource }) {
  // ...rest of the code remains same

  return (
    <AnimatedView style={{ top: -350 }}>
      <TapGestureHandler onGestureEvent={onDoubleTap} numberOfTaps={2}>
        {/* ...rest of the code remains same */}
      </TapGestureHandler>
    </AnimatedView>    
  );
}
Now, create two new shared values: translateX and translateY.
EmojiSticker.js
export default function EmojiSticker({ imageSize, stickerSource }) {
  const translateX = useSharedValue(0);
  const translateY = useSharedValue(0);

  // ...rest of the code remains same
}
These translation values will move the sticker around the screen. Since the sticker moves along both axes, we need to track the X and Y values separately.
In the useSharedValue() hooks, we have set both translation variables to have an initial position of 0. This means that the position the sticker is initially placed is considered the starting point. This value sets the initial position of the sticker when the gesture starts.
In the previous step, we triggered the onActive() callback for the tap gesture inside the useAnimatedGestureHandler() function. Similarly, for the pan gesture, we have to specify two callbacks:
  • onStart(): when the gesture starts or is at its initial position
  • onActive(): when the gesture is active and is moving
Create an onDrag() method to handle the pan gesture.
EmojiSticker.js
const onDrag = useAnimatedGestureHandler({
  onStart: (event, context) => {
    context.translateX = translateX.value;
    context.translateY = translateY.value;
  },
  onActive: (event, context) => {
    translateX.value = event.translationX + context.translateX;
    translateY.value = event.translationY + context.translateY;
  },
});
Both the onStart and onActive methods accept event and context as parameters. In the onStart method, we'll use context to store the initial values of translateX and translateY. In the onActive callback, we'll use the event to get the current position of the pan gesture and context to get the previously stored values of translateX and translateY.
Next, use the useAnimatedStyle() hook to return an array of transforms.For the <AnimatedView> component, we need to set the transform property to the translateX and translateY values. This will change the sticker's position when the gesture is active.
EmojiSticker.js
const containerStyle = useAnimatedStyle(() => {
  return {
    transform: [
      {
        translateX: translateX.value,
      },
      {
        translateY: translateY.value,
      },
    ],
  };
});
Then add the containerStyle from the above snippet on the <AnimatedView> component to apply the transform styles. Also, update the <EmojiSticker> component so that the <PanGestureHandler> component becomes the top-level component.
Handle pan gesture
export default function EmojiSticker({ imageSize, stickerSource }) {
  // rest of the code

  return (
    <PanGestureHandler onGestureEvent={onDrag}>
      <AnimatedView style={[containerStyle, { top: -350 }]}>
        <TapGestureHandler onGestureEvent={onDoubleTap} numberOfTaps={2}>
          <AnimatedImage
            source={stickerSource}
            resizeMode="contain"
            style={[imageStyle, { width: imageSize, height: imageSize }]}
          />
        </TapGestureHandler>
      </AnimatedView>
    </PanGestureHandler>
  );
}
Let's take a look at our app on iOS, Android and the web:

Up next

We successfully implemented pan and tap gestures.
In the next chapter, we'll learn how to take a screenshot of the image and the sticker, and save it on the device's library.
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