Question

我正在尝试创建状态副本，更新该副本并将其分配回该状态，但会引发错误。

这是我的代码：

class App extends Component {
  constructor(){
    super()
    this.State = {
      user: {
        username: '',
        password: ''
      }
    }
  }
  updateuser = (attr, event) => {
    console.log(attr + '==' + event.target.value);
    let updateduser = Object.assign({}, this.state.user) // errored line
    updateduser[attr] = event.target.value

    this.setState({
      user: updateduser
    })
  }

控制台错误：

App.js:17 Uncaught TypeError: Cannot read property 'user' of null
    at App._this.updateuser (App.js:17)
    at HTMLUnknownElement.callCallback (react-dom.development.js:147)
    at Object.invokeGuardedCallbackDev (react-dom.development.js:196)
    at invokeGuardedCallback (react-dom.development.js:250)
    at invokeGuardedCallbackAndCatchFirstError (react-dom.development.js:265)

Answer 1

这只是一个错字，请将 this.State 更改为 this.state ，

class App extends Component {
  constructor(){
    super()
    this.state = { //fix
      user: {
        username: '',
        password: ''
      }
    }
  }

  updateuser = (attr, event) => {
    console.log(attr + '==' + event.target.value);
    let updateduser = Object.assign({}, this.state.user) // errored line
    updateduser[attr] = event.target.value

    this.setState({
      user: updateduser
    })
  }

Answer 2

只需将this.State更新为this.state

怎么修。 TypeError：无法读取null的属性“ user”

2 个答案: