reactjs - 父状态更改后，React 子组件未更新

Question

我正在尝试制作一个漂亮的 ApiWrapper 组件来填充各种子组件中的数据。从我读过的所有内容来看，这应该有效:https://jsfiddle.net/vinniejames/m1mesp6z/1/

class ApiWrapper extends React.Component {

  constructor(props) {
    super(props);

    this.state = {
      response: {
        "title": 'nothing fetched yet'
      }
    };
  }

  componentDidMount() {
    this._makeApiCall(this.props.endpoint);
  }

  _makeApiCall(endpoint) {
    fetch(endpoint).then(function(response) {
      this.setState({
        response: response
      });
    }.bind(this))
  }

  render() {
    return <Child data = {
      this.state.response
    }
    />;
  }
}

class Child extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      data: props.data
    };
  }

  render() {
    console.log(this.state.data, 'new data');
    return ( < span > {
      this.state.data.title
    } < /span>);
  };
}

var element = < ApiWrapper endpoint = "https://jsonplaceholder.typicode.com/posts/1" / > ;

ReactDOM.render(
  element,
  document.getElementById('container')
);

但由于某种原因，当父状态发生变化时，子组件似乎没有更新。

我在这里遗漏了什么吗？

Answer 1

您的代码有两个问题。

您的子组件的初始状态是通过 props 设置的。

this.state = {
  data: props.data
};

引用此SO Answer :

Passing the intial state to a component as a prop is an anti-pattern because the getInitialState (in our case the constuctor) method is only called the first time the component renders. Never more. Meaning that, if you re-render that component passing a different value as a prop, the component will not react accordingly, because the component will keep the state from the first time it was rendered. It's very error prone.

因此，如果无法避免这种情况，理想的解决方案是使用方法 componentWillReceiveProps监听新的 props。

将以下代码添加到您的子组件中将解决子组件重新渲染的问题。

componentWillReceiveProps(nextProps) {
  this.setState({ data: nextProps.data });  
}

第二个问题与fetch有关。

_makeApiCall(endpoint) {
  fetch(endpoint)
    .then((response) => response.json())   // ----> you missed this part
    .then((response) => this.setState({ response }));
}

这是一个工作 fiddle :https://jsfiddle.net/o8b04mLy/