React)자식 컴포넌트가 부모컴포넌트로 state 보내는 방법 = Lifting State Up

(자식방향) ExpenseForm => NewExpense => App.js (부모방향)

ExpenseForm => NewExpense

원래는 자식에 있는 function을, 부모컴포넌트에서 만들어서 자식컴포넌트에 props로 주고, 자식에서 파생된 state(데이터)를 부모에서 내려준 function의 파라미터로 받게한다.

핵심은 자식 컴포넌트에 부모컴포넌트에서 만든 function을 프롭스로 내려주는것

//App.js

import React from "react";
import Expenses from "./components/Expenses/Expenses";
import NewExpense from "./components/NewExpense/NewExpense";

const App = () => {
  const expenses = [
    {
      id: "e1",
      title: "Toilet Paper",
      amount: 94.12,
      date: new Date(2020, 7, 14),
    },
    { id: "e2",
	title: "New TV",
	 amount: 799.49,
     	date: new Date(2021, 2, 12) },
    {
      id: "e3",
      title: "Car Insurance",
      amount: 294.67,
      date: new Date(2021, 2, 28),
    },
    {
      id: "e4",
      title: "New Desk (Wooden)",
      amount: 450,
      date: new Date(2021, 5, 12),
    },
  ];

  return (
    <div>
      <NewExpense/>
      <Expenses items={expenses}/>
    </div>
  );
};

export default App;

---

//NewExpense.js
import React from 'react';
import "./NewExpense.css";


import ExpenseForm from './ExpenseForm';

const saveExpenseDataHandler = ( enteredExpenseData )=> {
    const expenseData ={
        ...enteredExpenseData,
        id:Math.random().toString()
    };
    console.log(expenseData);
};

const NewExpense = () => {
    return (
        <div className="new-expense">
           <ExpenseForm onSaveExpenseData = { saveExpenseDataHandler } />
        </div>
    );
};

export default NewExpense;

---

//ExpenseForm.js

import React, { useState } from 'react';
import "./ExpenseForm.css"

const ExpenseForm = (props) => {
    const [enteredTitle,setEnteredTitle] = useState("");
    const [enteredAmount,setEnteredAmount] = useState("");
    const [enteredDate,setEnteredDate] = useState("");

    const titleChangeHandler = (event) => {
        setEnteredTitle(event.target.value);
    };
    const amountChangeHandler = (e)=> {
        setEnteredAmount(e.target.value);
    };
    const dateChangeHandler = (e)=> {
        setEnteredDate(e.target.value);
    };
    const submitHandler=(event)=>{
        event.preventDefault();

        const expenseData = {
            title: enteredTitle,
            amount: enteredAmount,
            date: new Date(enteredDate),
        }
        props.onSaveExpenseData();
        
        setEnteredTitle("");
        setEnteredAmount("");
        setEnteredDate("");
    };

    return (
       <form onSubmit={submitHandler}>
           <div className="new-expense__controls">
                <div className="new-expense__control">
                   <label>Title</label>
                   <input type="text" value={enteredTitle} onChange={titleChangeHandler} />
                </div>
                <div className="new-expense__control">
                    <label>Amount</label>
                    <input type="number" min="10" step="10" value={enteredAmount} onChange={amountChangeHandler}/>
                </div>
                <div className="new-expense__control">
                    <label>Date</label>
                    <input type="date" min="2019-01-01" max="2022-12-31" value={enteredDate} onChange={dateChangeHandler}/>
                </div>
           </div>
           <div className="new-expense__actions">
               <button type="submit">Add Expense</button>
           </div>
       </form>
    );
};

export default ExpenseForm;

NewExpense => App.js

1. App.js 컴포넌트에 function을 만들어준다

//App.js
import React from "react";
import Expenses from "./components/Expenses/Expenses";
import NewExpense from "./components/NewExpense/NewExpense";

const App = () => {
  const expenses = [
    {
      id: "e1",
      title: "Toilet Paper",
      amount: 94.12,
      date: new Date(2020, 7, 14),
    },
    { id: "e2",
     title: "New TV",
     amount: 799.49,
     date: new Date(2021, 2, 12) },
    {
      id: "e3",
      title: "Car Insurance",
      amount: 294.67,
      date: new Date(2021, 2, 28),
    },
    {
      id: "e4",
      title: "New Desk (Wooden)",
      amount: 450,
      date: new Date(2021, 5, 12),
    },
  ];

  const addExpenseHandler = (expense)=> {
    console.log('in app.js');
    console.log(expense);
  }

  return (
    <div>
      <NewExpense onAddExpense = { addExpenseHandler }/>
      <Expenses items={expenses}/>
    </div>
  );
};

export default App;

---

//NewExpense.js

import React from "react";
import "./NewExpense.css";
import ExpenseForm from "./ExpenseForm";

const NewExpense = (props) => {

  const saveExpenseDataHandler = (enteredExpenseData) => {
    const expenseData = {
      ...enteredExpenseData,
      id: Math.random().toString(),
    };
    자식 컴포넌트에서 생긴 데이터를 부모 컴포넌트에서 프롭스로 받은 function에 parameter로 넘겨준다.
    props.onAddExpense(expenseData);
  };

  return (
    <div className="new-expense">
      <ExpenseForm onSaveExpenseData={saveExpenseDataHandler} />
    </div>
  );
};

export default NewExpense;