為什麼我無法將 const 變數傳輸到不同的 React 文件

Question

所以我試著將 const 變數從一個檔案傳輸到另一個檔案。由於某種原因，我無法訪問它，並且它不允許我在文字檔案中顯示它。下面分別是 homepage.js 程式碼和 pay.js 檔案。我正在嘗試將 displayedAmount 變數從主頁文件傳輸到付費文件，然後將其顯示在文字元素中。但是，當我這樣做時，我收到此錯誤“錯誤：文字字串必須在組件內呈現。”

import { StyleSheet, Text, View, Image, Dimensions, TouchableOpacity, Alert, Animated } from 'react-native';
import { FontAwesome5 } from '@expo/vector-icons';
import React, { useState, useEffect, useRef } from 'react';
import { useNavigation } from '@react-navigation/native';
import pay from './pay';

const homepage = ({ route, navigation }) => {
  const [selectedAmount, setSelectedAmount] = useState("0");
  const [displayedAmount, setDisplayedAmount] = useState("0");
  const fadeAnim = new Animated.Value(0);  // initial opacity
  const screenWidth = Dimensions.get('window').width;
  const buttonWidth = screenWidth * 0.45;
  const spaceBetweenNumbers = 100;
  
  
  useEffect(() => {
    Animated.timing(
      fadeAnim,
      {
        toValue: 1,
        duration: 1000,
        useNativeDriver: true,
      }
    ).start();
    
    if (selectedAmount.includes('.')) {
        const [whole, decimal] = selectedAmount.split('.');
        setDisplayedAmount(`${isNaN(parseInt(whole)) ? "0" : parseInt(whole).toLocaleString()}.${decimal}`);
      } else {
        setDisplayedAmount(isNaN(parseInt(selectedAmount)) ? "0" : parseInt(selectedAmount).toLocaleString());
      }

    Animated.timing(
      fadeAnim,
      {
        toValue: 0,
        duration: 1000,
        useNativeDriver: true,
      }
    ).start();

  }, [selectedAmount]);

  const handleNumberPress = (number) => {
    if (selectedAmount.length < 5) {
      setSelectedAmount(prevState => prevState === "0" ? String(number) : prevState + number);
    }
  };

  const handleDecimalPress = () => {
    if (!selectedAmount.includes(".") && selectedAmount.length < 4) {
      setSelectedAmount(prevState => prevState + ".");
    }
  };

  const handleDeletePress = () => {
    setSelectedAmount(prevState => prevState.slice(0, -1) || "0");
  };
  const goTopay = () => {
    navigation.navigate('Pay', { displayedAmount }); // passing displayedAmount as a parameter
  };

import { StyleSheet, Text, TouchableOpacity, View } from 'react-native';
 import React from 'react';
 import { Feather } from '@expo/vector-icons';
 import { createStackNavigator } from '@react-navigation/stack';
 import homepage from './homepage';
 import displayedAmount from './homepage'
 
 
 const Pay = ({ route, navigation }) => {
     const { displayedAmount } = route.params;
     const goToHome = () => {
     navigation.navigate('Homepage'); // The corrected screen name should be 'Homepage' instead of 'homepage'
   };
 
   return (
     <View>
       <TouchableOpacity onPress={goToHome}>
         <Feather name="x" color="black" size={30} style={styles.cross} />
       </TouchableOpacity>
       <View
   style={{
     borderBottomColor: 'grey',
     borderBottomWidth: StyleSheet.hairlineWidth,
     marginTop: 95,
   }}
 />
 <Text style={styles.to}>To</Text>
 <View
   style={{
     borderBottomColor: 'grey',
     borderBottomWidth: StyleSheet.hairlineWidth,
     marginTop: 55,
   }}
 />
 <Text style={styles.for}>For</Text>
 <View
   style={{
     borderBottomColor: 'grey',
     borderBottomWidth: StyleSheet.hairlineWidth,
     marginTop: 55,
   }}
 />
 <Text>{displayedAmount}</Text> {/* Display the displayedAmount */}
     </View>
     
   );
 };
 
 export default Pay;
 
 const styles = StyleSheet.create({
   cross: {
     position: 'absolute',
     left: 15,
     top: 50,
   },
   to:{
     fontFamily: 'CashMarketMedium',
     fontSize: 16,
     position: 'absolute',
     left: 19,
     top: 110,
   },
   for:{
     fontFamily: 'CashMarketMedium',
     fontSize: 16,
     position: 'absolute',
     left: 19,
     top: 165,
   },
   line: {
     position: 'absolute',
     left: 15,
     top: 50 + 36 + 4, // To position the line below the 'x' icon, we add its size (36) and some margin (4)
     width: '100%',
     height: 1,
     backgroundColor: 'grey',
   },
 });

Answer 1

幾個選項：

1. 對於靜態值，匯出非巢狀const 中的值。通常將常數分開，這樣，如果兩個元件需要相同的常數，而其中一個元件需要另一個元件，則不會建立 require 迴圈。僅供參考，導出常數命名為導出 VS 預設導出。所以需要用大括號導入。

//constants file
export const value1 = '123456'

// component file
import { value1 } from '../constants'

2. 對於需要跨應用程式匯出的有狀態值，請查看 React.Context API 或全域狀態管理庫。
3. 對於子元件，您可以透過 props 將資料傳遞給元件。
4. 對於 React-navigation 畫面導航，您可以透過 params 物件將參數傳送到螢幕。