Select 值在使用 setSate React 时第一次触发 onChange 事件时没有改变

Question

I have a set of select menus and I am trying to change a value when I select an option using onChange={updateValue} event. When I first select an option, the value is not being updated in the select menu. It only changes the second time I try to choose an option. Not sure what I am doing wrong.

Edit: I did some more research ( OnChange event using React JS for drop down ) and I believe I need the value of the select to be updated as well, using setState. I cant figure out how to do it without having a variable for each value and set the state again.

let selectMenus = [
  {
    id: 'id1',
    name: 'name1',
    label: 'label1',
    value: '0',
    options: [
      {
        text: 'All ages',
        value: '0',
      },
      {
        text: '35 - 37 yrs',
        value: '1',
      },
    ],
    buttonLabel: 'Refresh',
  },
  {
    id: 'id2',
    name: 'name2',
    label: 'label2',
    value: '1',
    options: [
      {
        text: 'All ages',
        value: '0',
      },
      {
        text: '45 - 50 yrs',
        value: '1',
      },
    ],
    buttonLabel: 'Refresh',
  },
];

const [url, setUrl] = useState('http://localhost:5000/selectDropdowns1');

const updateValue = () => {
  setUrl('http://localhost:5000/selectDropdowns2');
};

<form>
  {selectMenus.map((select) => (
    <div key={select.id} className='select-container'>
      <label htmlFor={select.id}>{select.label}</label>
      <select id={select.id} name={select.name} value={select.value} onChange={updateValue}>
        {select.options.map((option) => (
          <option value={option.value} key={uuid()}>
            {option.text}
          </option>
        ))}
      </select>
      <button>{select.buttonLabel}</button>
    </div>
  ))}
</form>;

Answer 1

The problem is that when you provide onChange prop to select component it become a controlled component .

For more information: React Docs - Forms #controlled components

When you dealing with controlled components you must provide a value to it and when onChange triggerd it should update that value to work properly. Since you did not provide the full code, I imagine you have an array of select menus and options attached to it.

So in this case every select component should have own onChange method and own value to work properly. To achive this we should create another component for only Select Options. Like this;

function SelectComponent({ optionList, onSelected }) {
  const [value, setValue] = useState();

  const updateValue = ({ target }) => {
    setValue(target.value);
    if (onSelected) onSelected(target.value);
  };

  return (
    <>
      <label htmlFor={optionList.id}>{optionList.label}</label>
      <select
        id={optionList.id}
        name={optionList.name}
        value={value}
        onChange={updateValue}
      >
        {optionList.options.map((option) => (
          <option value={option.value} key={uuid()}>
            {option.text}
          </option>
        ))}
      </select>
      <button>{optionList.buttonLabel}</button>
    </>
  );
}

This component accepts to props; optionList and onSelected

optionList is the list of options to render

onSelected is a method that we call when user select and option

On main component, we should change the select section with our select component with props optionList and onSelected

  return (
    <div>
      {selectMenus.map((select) => (
        <div key={select.id} className="select-container">
          <SelectComponent optionList={select} onSelected={updateValue} />
        </div>
      ))}
    </div>
  );

So overall code is like this:

import { useState } from "react";
import { v4 as uuid } from "uuid";

export default function App() {
  const [url, setUrl] = useState();

  const updateValue = (value) => {
    setUrl(value);
  };

  const selectMenus = [
    {
      id: 1,
      label: "Menu 1",
      name: "menu1",
      buttonLabel: "Menu 1",
      options: [
        {
          text: "option 1",
          value: "option1"
        },
        {
          text: "option 2",
          value: "option2"
        },
        {
          text: "option 3",
          value: "option3"
        }
      ]
    },
    {
      id: 2,
      label: "Menu 2",
      name: "menu2",
      buttonLabel: "Menu 2",
      options: [
        {
          text: "option 1",
          value: "option1"
        },
        {
          text: "option 2",
          value: "option2"
        },
        {
          text: "option 3",
          value: "option3"
        }
      ]
    },
    {
      id: 3,
      label: "Menu 3",
      name: "menu3",
      buttonLabel: "Menu 3",
      options: [
        {
          text: "option 1",
          value: "option1"
        },
        {
          text: "option 2",
          value: "option2"
        },
        {
          text: "option 3",
          value: "option3"
        }
      ]
    }
  ];

  return (
    <div className="App">
      <h1>URL Value: {url}</h1>
      {selectMenus.map((select) => (
        <div key={select.id} className="select-container">
          <SelectComponent optionList={select} onSelected={updateValue} />
        </div>
      ))}
    </div>
  );
}

function SelectComponent({ optionList, onSelected }) {
  const [value, setValue] = useState();

  const updateValue = ({ target }) => {
    setValue(target.value);
    if (onSelected) onSelected(target.value);
  };

  return (
    <>
      <label htmlFor={optionList.id}>{optionList.label}</label>
      <select
        id={optionList.id}
        name={optionList.name}
        value={value}
        onChange={updateValue}
      >
        {optionList.options.map((option) => (
          <option value={option.value} key={uuid()}>
            {option.text}
          </option>
        ))}
      </select>
      <button>{optionList.buttonLabel}</button>
    </>
  );
}

Working example is overhere codesandbox