Category: JavaScript

Sometimes, we want to get the current value of Animated.Value with React Native.

In this article, we’ll look at how to get the current value of Animated.Value with React Native.

How to get the current value of Animated.Value with React Native?

To get the current value of Animated.Value with React Native, we call addListener on the animated value object.

For instance, we write:

import * as React from 'react';
import { View, Animated, Text, Easing } from 'react-native';
import Constants from 'expo-constants';
import { Card } from 'react-native-paper';

const spinValue = new Animated.Value(0);

export default function App() {
  React.useEffect(() => {
    spinValue.addListener(({ value }) => console.log(value));
    Animated.timing(spinValue, {
      toValue: 1,
      duration: 3000,
      easing: Easing.linear,
      useNativeDriver: true,
    }).start();
  }, []);

  const spin = spinValue.interpolate({
    inputRange: [0, 1],
    outputRange: ['0deg', '360deg'],
  });

  return (
    <Animated.Image
      style={{ transform: [{ rotate: spin }], width: 200, height: 300 }}
      source={{ uri: 'https://picsum.photos/200/300' }}
    />
  );
}

to call spinValue.addListener with a callback to get the current value of the animated value from the value property.

We create an animated value with Animated.Value and call Animated.timing to create the animation.

Then we call start to start the animation.

As a result, we should see the value logged as the animation is being run.

Conclusion

To get the current value of Animated.Value with React Native, we call addListener on the animated value object.

Sometimes, we want to animate the rotation of an Image with React Native.

In this article, we’ll look at how to animate the rotation of an Image with React Native.

How to animate the rotation of an Image with React Native?

To animate the rotation of an Image with React Native, we can use the animated value’s interpolate method.

For instance, we write:

import * as React from 'react';
import { View, Animated, Text, Easing } from 'react-native';
import Constants from 'expo-constants';
import { Card } from 'react-native-paper';

const spinValue = new Animated.Value(0);

export default function App() {
  React.useEffect(() => {
    Animated.timing(spinValue, {
      toValue: 1,
      duration: 3000,
      easing: Easing.linear,
      useNativeDriver: true,
    }).start();
  }, []);

  const spin = spinValue.interpolate({
    inputRange: [0, 1],
    outputRange: ['0deg', '360deg'],
  });

  return (
    <Animated.Image
      style={{ transform: [{ rotate: spin }], width: 200, height: 300 }}
      source={{ uri: 'https://picsum.photos/200/300' }}
    />
  );
}

to add the Animated.Image component to add an image that can animate.

Then we define the spinValue animated value with Animated.Value.

Next, we call Animated.timing with spinValue and some options for the animation.

toValue is the value of the inputValue to animate to.

duration is the duration of the animation in milliseconds.

easing is the easing.

Next, we call spinValue.interpolate to interpolate the animation values.

We call start to start the animation in the useEffect callback.

Conclusion

To animate the rotation of an Image with React Native, we can use the animated value’s interpolate method.

Sometimes, we want to animate backgroundColor in React Native.

In this article, we’ll look at how to animate backgroundColor in React Native.

How to animate backgroundColor in React Native?

To animate backgroundColor in React Native, we can use the animated value’s interpolate method.

For instance, we write:

import * as React from 'react';
import { View, Animated, Text } from 'react-native';
import Constants from 'expo-constants';
import { Card } from 'react-native-paper';

const c = new Animated.Value(0);

export default function App() {
  React.useEffect(() => {
    Animated.timing(c, {
      toValue: 300,
      duration: 3000,
    }).start();
  }, []);

  const color = c.interpolate({
    inputRange: [0, 200, 300],
    outputRange: ['orange', 'lightgreen', 'yellow'],
  });

  return (
    <Animated.View style={{ backgroundColor: color }}>
      <Text>hello world</Text>
    </Animated.View>
  );
}

to create a new animated value with Animated.Value.

Then we call Animated.timing to create the animation.

We specify the toValue to animate to the value of the inputRange we specify.

And we specify the duration of the animation in milliseconds.

Finally, we specify the color values to animate in the outputRange and set the color as the value of the backgroundColor.

As a result, we should see the color change for 3 seconds when the page loads.

Conclusion

To animate backgroundColor in React Native, we can use the animated value’s interpolate method.

Sometimes, we want to add a ListView grid in React Native

In this article, we’ll look at how to add a ListView grid in React Native.

How to add a ListView grid in React Native?

To add a ListView grid in React Native, we should use a FlatList instead with some flexbox styles.

For instance, we write:

import * as React from 'react';
import { View, FlatList, Text, StyleSheet, Dimensions } from 'react-native';
import Constants from 'expo-constants';
import { Card } from 'react-native-paper';

const numColumns = 3;
const size = Dimensions.get('window').width / numColumns;

const styles = StyleSheet.create({
  itemContainer: {
    width: size,
    height: size,
  },
  item: {
    flex: 1,
    margin: 3,
    backgroundColor: 'lightblue',
  },
});

const data = Array(200)
  .fill()
  .map((_, i) => ({ id: i, value: i }));

export default function App() {
  return (
    <FlatList
      data={data}
      renderItem={({ item }) => (
        <View style={styles.itemContainer}>
          <Text style={styles.item}>{item.value}</Text>
        </View>
      )}
      keyExtractor={(item) => item.id}
      numColumns={numColumns}
    />
  );
}

to add the itemContainer style property that sets the width and height of the container.

Then we render a FlatList with the data array set as the value of the data prop.

Then we set the renderItem prop to a function to render items in the FlatList.

We set numColumns to set the number of columns.

keyExtractor is set to a function that returns the unique key for each item.

Conclusion

To add a ListView grid in React Native, we should use a FlatList instead with some flexbox styles.

Sometimes, we want to scroll to top of the ScrollView with React Native.

In this article, we’ll look at how to scroll to top of the ScrollView with React Native.

How to scroll to top of the ScrollView with React Native?

To scroll to top of the ScrollView with React Native, we assign a ref to the ScrollView and call scrollTo on the ref’s value.

For instance, we write:

import * as React from 'react';
import { ScrollView, View, Text, Button } from 'react-native';
import Constants from 'expo-constants';
import { Card } from 'react-native-paper';

export default function App() {
  const ref = React.useRef();

  return (
    <View
      style={{
        flexGrow: 1,
      }}>
      <Button
        title="scroll to top"
        onPress={() => {
          ref.current.scrollTo(0);
        }}
      />
      <ScrollView ref={ref} style={{ height: 200 }}>
        {Array(200)
          .fill()
          .map((_, i) => {
            return <Text>{i}</Text>;
          })}
      </ScrollView>
    </View>
  );
}

to create a ref with useRef and set that as the value of the ref prop of the ScrollView.

Then we add a Button that calls ref.current.scrollTo with 0 to scroll the ScrollView to the top when it’s pressed.

Conclusion

To scroll to top of the ScrollView with React Native, we assign a ref to the ScrollView and call scrollTo on the ref’s value.