React Native - unable to pass state variable into style

Question

My code fetches a json file, calculates a value and I want to pass this value into the style of TouchableOpacity. Below is my attempt:

const [height, setHeight] = useState(0)
const [isLoading, setLoader] = useState(true)

const fetching = async () => {
    ...//code that fetches the value
    setHeight(value)
    setLoader(false)
} 

if (isLoading) {
    return (
        <Text> Loading...</Text>
    )
}

return (
    <View>
        <TouchableOpacity
              style={{height: height, width:30, backgroundColor: "red" }} />
         ... //other parts of the return statement 
    </View>

)

the complete code:

<View style={{height: height}}>
     <TouchableOpacity
          style={{width:30, borderWidth:5, marginTop:20, backgroundColor:"blue", height:height}}>
     </TouchableOpacity>
</View>

Any help would be appreciated.

Answer 1

I think your useState is fine. However either the parent View doesn't have any space or the TouchableOpacity has nothing to display.

You can try to do:

return (
    <View>
        <TouchableOpacity
              style={{height, width:30, borderWidth: 5 }} />
         ... //other parts of the return statement 
    </View>
)

If you see no border, then it's a problem with the parent View

You can then try:

return (
    <View style={{flex: 1}}>
        <TouchableOpacity
              style={{height, width:30, borderWidth: 5 }} />
         ... //other parts of the return statement 
    </View>
)

You could also try adding a Text component with some text to the TouchableOpacity.

This code:

import React, { useEffect, useState } from 'react';
import {Text, View, TouchableOpacity} from 'react-native';

export default function App() {
  const [height, setHeight] = useState(0)
  const [isLoading, setLoader] = useState(true)

  useEffect(() => {
    const timerTask = setInterval(() => {
      setHeight(Math.random() * 200)
      setLoader(false);
    }, 5000);
    return () => clearInterval(timerTask);
  }, [])

  if (isLoading) {
    return (
      <Text> Loading...</Text>
    )
  }

  return (
    <View style={{flex: 1, alignItems: 'center', justifyContent: 'center' }}>
      <TouchableOpacity
        style={{width: 30, borderWidth: 5, marginTop: 20, backgroundColor: "blue", height}}>
      </TouchableOpacity>
    </View>
  )
}

Produces a blue touchable opacity that changes height every 5 seconds. Also when I touch it, it turns a lighter shade.