0

在下面的示例中,当我更新某个字段时,我的状态对象中的另一个字段消失/未设置,并且我收到有关输入变得不受控制的警告。下面的例子:

const {useState} = React;

const App = () => {
  const [user, setUser] = useState({ 
    firstName: 'Mary',
    lastName: 'Poppins',
  });
  
  return (
    <div>
      First Name: <input value={user.firstName} onChange={e => { 
        setUser({firstName: e.target.value});
      }} />
      <br />
      Last Name: <input value={user.lastName} onChange={e => { 
        setUser({lastName: e.target.value});
      }} />
      <br />
      {JSON.stringify(user, null, 2)}
    </div>
  );
};

ReactDOM.render(<App />, document.querySelector('#app'));
<script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script>
<div id="app"></div>

4

1 回答 1

3

正如 React 文档所述:

但是,与this.setState类不同,更新状态变量总是替换它而不是合并它。

因此 usingsetUser不会对对象进行浅合并,而是将状态替换为整个对象,这会导致其他字段消失。您可以在执行时使用Object.assign或 spread( ...) 运算符将对象合并在一起setUser

const {useState} = React;

const App = () => {
  const [user, setUser] = useState({ 
    firstName: 'Mary',
    lastName: 'Poppins',
  });
  
  return (
    <div>
      First Name: <input value={user.firstName} onChange={e => { 
        setUser(Object.assign({}, user, {firstName: e.target.value}));
      }} />
      <br />
      Last Name: <input value={user.lastName} onChange={e => { 
        setUser(Object.assign({}, user, {lastName: e.target.value}));
      }} />
      <br />
      {JSON.stringify(user, null, 2)}
    </div>
  );
};

ReactDOM.render(<App />, document.querySelector('#app'));
<script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script>
<div id="app"></div>

或者,创建一个名为的自定义钩子useMergeState,以帮助您像往常一样自动进行合并setState

于 2018-11-25T20:53:14.240 回答