how to make a simple character counter in my React Native with Expo

Hey guys,

I had build a simple character counter with React Native under the Expo Frame . However ,I had met a issue ,seems I can’t get the length of the input text … I have attached my code ,could you please help me to take a lool ?

Thank you so much!!

import React,{ useState } from 'react';
import { Text, View } from 'react-native';
import { StyleSheet } from 'react-native'
import AppTextInput from '../components/AppTextInput';
import AppFormFlied from './../components/AppFormFlied';
import AppButton from './../components/AppButton';

function CommentsHome(props) {
    const [value,setValue] = useState("");
    return (
        <View style={styles.container}>
        <AppTextInput icon='feather'
         placeholder="Left something.." 
         <Text>Character Left :{value.length === null ? 0 : value.length}/100</Text>
        <AppButton title="Submit"/>

const styles = StyleSheet.create({
    container  : {
        width  : "100%",
        justifyContent : "center",
        alignItems : 'center',
        flexDirection : 'column',
export default CommentsHome;