React native - "Rendered more hooks than during the previous render?"

Question

I only encountered this issue once I incorporated the useEffect() hook as suggested by React native - "this.setState is not a function" trying to animate background color?

With the following, I get

Rendered more hooks than during the previous render

export default props => {
      let [fontsLoaded] = useFonts({
        'Inter-SemiBoldItalic': 'https://rsms.me/inter/font-files/Inter-SemiBoldItalic.otf?v=3.12',
            'SequelSans-RomanDisp' : require('./assets/fonts/SequelSans-RomanDisp.ttf'),
            'SequelSans-BoldDisp' : require('./assets/fonts/SequelSans-BoldDisp.ttf'),
            'SequelSans-BlackDisp' : require('./assets/fonts/SequelSans-BlackDisp.ttf'),
      });
      if (!fontsLoaded) {
        return <AppLoading />;
      } else {
    
    //Set states
      const [backgroundColor, setBackgroundColor] = useState(new Animated.Value(0));

      useEffect(() => {
        setBackgroundColor(new Animated.Value(0));
      }, []);    // this will be only called on initial mounting of component,
      // so you can change this as your requirement maybe move this in a function which will be called,
      // you can't directly call setState/useState in render otherwise it will go in a infinite loop.
      useEffect(() => {
        Animated.timing(this.state.backgroundColor, {
          toValue: 100,
          duration: 5000
        }).start();
      }, [backgroundColor]);

      var color = this.state.colorValue.interpolate({
        inputRange: [0, 300],
        outputRange: ['rgba(255, 0, 0, 1)', 'rgba(0, 255, 0, 1)']
      });

    const styles = StyleSheet.create({
      container: { flex: 1,
      alignItems: 'center',
      justifyContent: 'center',
      backgroundColor: color
    },
      textWrapper: {
        height: hp('70%'), // 70% of height device screen
        width: wp('80%'),   // 80% of width device screen
        backgroundColor: '#fff',
        justifyContent: 'center',
        alignItems: 'center',
      },
      myText: {
        fontSize: hp('2%'), // End result looks like the provided UI mockup
        fontFamily: 'SequelSans-BoldDisp'
      }
    });

      return (
        <Animated.View style={styles.container}>
          <View style={styles.textWrapper}>
            <Text style={styles.myText}>Login</Text>
          </View>
        </Animated.View>
      );
  }
};

Im just trying to animate fade the background color of a view. I tried deleting the first useEffect in case it was causing some redundancy, but that did nothing. Im new to ReactNative - what is wrong here?

EDIT:

export default props => {
  let [fontsLoaded] = useFonts({
    'Inter-SemiBoldItalic': 'https://rsms.me/inter/font-files/Inter-SemiBoldItalic.otf?v=3.12',
        'SequelSans-RomanDisp' : require('./assets/fonts/SequelSans-RomanDisp.ttf'),
        'SequelSans-BoldDisp' : require('./assets/fonts/SequelSans-BoldDisp.ttf'),
        'SequelSans-BlackDisp' : require('./assets/fonts/SequelSans-BlackDisp.ttf'),
  });

  //Set states
    const [backgroundColor, setBackgroundColor] = useState(new Animated.Value(0));

    useEffect(() => {
      setBackgroundColor(new Animated.Value(0));
    }, []);    // this will be only called on initial mounting of component,
    // so you can change this as your requirement maybe move this in a function which will be called,
    // you can't directly call setState/useState in render otherwise it will go in a infinite loop.
    useEffect(() => {
      Animated.timing(useState(backgroundColor), {
        toValue: 100,
        duration: 7000
      }).start();
    }, [backgroundColor]);

    // var color = this.state.colorValue.interpolate({
    //   inputRange: [0, 300],
    //   outputRange: ['rgba(255, 0, 0, 1)', 'rgba(0, 255, 0, 1)']
    // });

//------------------------------------------------------------------->
  if (!fontsLoaded) {
    return <AppLoading />;
  } else {

    const styles = StyleSheet.create({
      container: { flex: 1,
      alignItems: 'center',
      justifyContent: 'center',
      backgroundColor: backgroundColor

New errors:

invalid prop 'color' supplied to 'Stylesheet'

Animated useNativeDriver was not specified

Answer 1

On your first render (I'm guessing) only the useFonts hook will be called as you return <AppLoading /> since !fontsLoaded . The rest of your hooks are in the else block, meaning you won't have the same number of hooks on every render.

Check out https://reactjs.org/docs/hooks-rules.html for more explanation, especially https://reactjs.org/docs/hooks-rules.html#only-call-hooks-at-the-top-level

Answer 2

The useNativeDriver error exists because you didn't specify it:

Your code:

useEffect(() => {
  Animated.timing(useState(backgroundColor), {
    toValue: 100,
    duration: 7000
}).start();

Fix:

useEffect(() => {
  Animated.timing(useState(backgroundColor), {
    toValue: 100,
    duration: 7000,
    useNativeDrive: true
}).start();

Hope this helps!