Trigger child component to re-render in parent component

Question

I'm using react-native to make an app. when onReserve() is implemented, I want ModalView to be updated. But it's not updated, value of usermachine in Modalview is the same as the value before onReserve() is implemented.

let first value of usermachine is [] and the value is changed to [{"id":"1"}] after onReserve() . but usermachine displayed on Modalview is still [] and let the value of usermachine is changed to [{"id":"2"}] after onReserve() is implemented once again,usermachine displayed on Modalview is [{"id":"1"}] .

How to update the value of usermachine displayed on Modalview right after onReserve() ?

ReserveScreen.js

import React, {useEffect, useState, useRef} from 'react';
import {
  SafeAreaView,
  ScrollView,
  StyleSheet,
  View,
  Alert,
  Button,
  Text,
  Modal,
  KeyboardAvoidingView,
} from 'react-native';
import ModalView from '../components/ModalView.js';
import MachineView from '../components/MachineView.js';
import AsyncStorage from '@react-native-async-storage/async-storage';

const ReserveScreen = ({navigation, route, category}) => {
  const [machines, setMachines] = useState([]);
  const [change1, setChange1] = useState(0); 
  function handlechange() {
    setChange1(change1 + 1);
  }

  const [loading, setLoading] = useState(0);
  const [loading2, setLoading2] = useState(0);

  const getmachineinfo = () => {
    setLoading2(loading2 + 1);
    fetch(
      'https://so6wenvyg8.execute-api.ap-northeast-2.amazonaws.com/dev/machine',
      {
        method: 'GET',
        headers: {
          Accept: 'application/json',
          'Content-Type': 'application/json',
        },
      },
    )
      .then(response => response.json())
      .then(json => {
        let machinelist = [];
        for (let k = 0; k < json.machinearr.length; k++) {
          let id1 = -1;
          let name1 = '';
          let category1 = -1;
          let waitnum1 = -1;
          for (let i = 0; i < json.machinearr[k].length - 1; i++) {
            switch (i) {
              case 0:
                id1 = Number(json.machinearr[k][i]);
                break; //machineid
              case 1:
                name1 = json.machinearr[k][i];
                break; //machinename
              case 2:
                category1 = Number(json.machinearr[k][i]);
                break; //machinecategory
              case 3:
                continue; //machineimage
              case 4:
                waitnum1 = json.machinearr[k][i].length;
                break; //waitnumber
            }
          }
          let object = {
            name: name1,
            id: id1,
            waitnum: waitnum1,
            category: category1,
          };
          machinelist.push(object);
        }
        setMachines(machinelist);
        setTimeout(() => {
          setLoading(loading+1);
        }, 1000);
      })
      .catch(error => {
        console.error(error);
        return -1;
      });
  };
  useEffect(() => {
    console.log('useeffect');
    getmachineinfo();
  }, [change1]); 

  const [username, setUsername] = useState(''); 
  

  const getusername = async () => {
    try {
      const name = await AsyncStorage.getItem('@storage_username');
      setUsername(name);
      return;
    } catch (e) {
      console.log(e);
    }
  };
  getusername();
  
  const [userid,setUserid]=useState('');
  const getuserid= async()=>{
    const value = await AsyncStorage.getItem('@storage_userid');
    if (value !== null){
        setUserid(value);
    }
  }
  getuserid();
  
  const [myres, setMyres] = useState([]);
  const [loading3, setLoading3] = useState(0);
  const [loading4, setLoading4] = useState(0);
  const [usermachine, setUserMachine] = useState([]);

  const myReserve = () => {
          if (userid !== null) {
        const url =
          'https://so6wenvyg8.execute-api.ap-northeast-2.amazonaws.com/dev/reservation?userid=' +
          userid;
        fetch(url, {
          method: 'GET',
          headers: {
            Accept: 'application/json',
            'Content-Type': 'application/json',
          },
        })
          .then(response => response.json())
          .then(json => {
            Alert.alert(JSON.stringify(json));
            setMyres(json["reservation"]);
            setUserMachine(myres);
            setLoading4(loading4 + 1);
            handlechange();
            return myres;
          })
          .catch(error => {
            console.error(error);
          });
      }
    handlechange();
        
  };

  const [isreserved, setIsReserved] = useState(false);

  const onmyReserve = () => {
    setLoading3((loading3)=>{return loading3+1});
     myReserve();
    setTimeout(() => {
      if (myres.length > 0) {
        setIsReserved(true);
      } else {
        setIsReserved(false);
      }
         }, 2000);
  }; 

  const [visible, setVisible] = useState(false); 

  return (
    <SafeAreaView style={{flex: 1, backgroundColor: 'white'}}>
      <Modal transparent={true} visible={visible} animationType="slide">
        <View style={styles.modalContainer}>
          <View style={styles.modalContent}>
            {loading3!=loading4?(<View style={{flex: 7, justifyContent: 'center', alignItems: 'center'}}>
          <View style={{flex: 1}} />
          <Text>현재 예약가능한 기구가 없습니다.</Text>
          <View style={{flex: 5}} />
        </View>):(<ModalView
              isreserved={isreserved}
              usermachine={usermachine}
              handlerFunction={handlechange}
              change1={change1}></ModalView>)}
            
            <Button
              title={'확인'}
              onPress={() => {
                setVisible('false');
              }}></Button>
          </View>
        </View>
      </Modal>
      <View style={styles.btn1view}>
        <Button
          title="나의 예약내역 조회/수정"
          color={'#26a96a'}
          onPress={() => {
            onmyReserve();
            setVisible(true);
          }}
        />
      </View>
      <View style={styles.seperator}></View>
      {loading != loading2 ? (
        <View style={{flex: 7, justifyContent: 'center', alignItems: 'center'}}>
          <View style={{flex: 1}} />
          <Text>현재 예약가능한 기구가 없습니다.</Text>
          <View style={{flex: 5}} />
        </View>
      ) : (
        <MachineView
          machine={machines}
          handlerFunction={handlechange}
          change1={change1}></MachineView>
      )}
      <View style={{height: '5%'}}></View>
    </SafeAreaView>
  );
};

const styles = StyleSheet.create({
  seperator: {
    height: 1,
    backgroundColor: 'black',
    marginVertical: 10,
  },
  btn1view: {
    flex: 0.6,
    backgroundColor: 'white',
    flexDirection: 'row-reverse',
    alignItems: 'center',
  },
  categoryView: {
    flex: 0.5,
    backgroundColor: 'white',
    flexDirection: 'row',
    justifyContent: 'space-around',
  },
  sortView: {flex: 0.5, flexDirection: 'row', marginLeft: 10},
  scrollView: {flex: 6, backgroundColor: 'white'},
  modalContainer: {
    flex: 1,
    padding: 20,
    justifyContent: 'center',
  },
  modalContent: {
    flex: 0.5,
    backgroundColor: 'white',
    alignItems: 'center',
    justifyContent: 'center',
    borderColor: 'black',
    borderWidth: 4,
    borderRadius: 20,
  },
});

export default ReserveScreen;

ModalView.js

import React from 'react';
import {View, Text, Button, StyleSheet} from 'react-native';
import MachineModal from './MachineModal.js';
import Icon from 'react-native-vector-icons/MaterialIcons';
const ModalView = ({isreserved, usermachine, change1, handlerFunction}) => {
  const change2 = change1;
  function handleChange() {
    handlerFunction();
    console.log('handlechange()');
  }
  
  {
      return (
        <View>
          <Text>나의 예약내역</Text>
          {usermachine.map(item => {
            return (
              <View key={item.id}>
                <MachineModal
                  name={item.name}
                  id={item.id}
                  waitnum={item.waitnum}
                  change2={change2}
                  handlerFunction={handleChange}></MachineModal>
              </View>
            );
          })}
        </View>
      );
    
  }
};

const styles = StyleSheet.create({});
export default ModalView;

MachineModal.js

import React, {useState} from 'react';
import {View, Text, Button, Alert, StyleSheet, Image} from 'react-native';
import AsyncStorage from '@react-native-async-storage/async-storage'; 


const MachineModal = ({name, id, waitnum, change2, handlerFunction}) => {
  const formatted = `기구명 : ${name}\n\n현재 대기인원 : ${waitnum}명`;
  const [userid, setUserid] = useState('');
  const getusername = async () => {
    try {
      const uid = await AsyncStorage.getItem('@storage_userid');
      setUserid(uid);
      return;
    } catch (e) {
      console.log(e);
    }
  };
  getusername();

  const change3 = change2;
  function handlechange1() {
    handlerFunction();
  }

  const machinereturn = (machineid, usid) => {
    try {
      fetch(
        'https://so6wenvyg8.execute-api.ap-northeast-2.amazonaws.com/dev/return',
        {
          method: 'POST',
          headers: {
            Accept: 'application/json',
            'Content-Type': 'application/json',
          },
          body: JSON.stringify({
            machineid: String(machineid),
            userid: String(usid),
          }),
        },
      )
        .then(response => response.json())
        .then(json => {
          console.log(json);
          try {
            tim = json['time'];
            handlechange1();
            Alert.alert('반납되었습니다.');
            return 1;
          } catch (e) {
            handlechange1();
            Alert.alert('반납에 실패했습니다.');
            return -1;
          }
        });
    } catch (e) {
      console.log('17');
      console.log(e);
    }
  };

  return (
    <View style={styles.machine}>
      <Image
        source={require('../images/default_image.png')}
        style={{width: 70, height: 70}}></Image>
      <Text>{formatted}</Text>
      <Button
        title="예약취소"
        onPress={() => machinereturn(id, userid)}></Button>
    </View>
  );
};

const styles = StyleSheet.create({
  machine: {
    flexDirection: 'row',
    justifyContent: 'space-around',
    paddingTop: 7,
    paddingBottom: 7,
    borderBottomColor: 'black',
    borderBottomWidth: 1,
    alignItems: 'center',
  },
});
export default MachineModal;

Answer 1

You aren't calling setUserMachine with the result of json . You're setting it to myres , which isn't updated to json["reservation"] yet. This is a pretty common misunderstanding of React. State updates don't happen until after your component function has ran.

Also, you should put stuff like getusername inside an effect. Otherwise functions like getusername will be called on every render.