componentDidUpdate()中的setState()

Question

我正在编写一个脚本,根据下拉的高度和屏幕上输入的位置,将输入下移或高于输入.另外,我想根据其方向将修改器设置为下拉列表.但是setState在内部使用componentDidUpdate会创建一个无限循环(很明显)

我已经找到了getDOMNode直接使用和设置classname到dropdown 的解决方案,但我觉得使用React工具应该有更好的解决方案.有谁能够帮我？

这是工作代码的一部分getDOMNode(有点忽略定位逻辑以简化代码)

let SearchDropdown = React.createClass({
    componentDidUpdate(params) {
        let el = this.getDOMNode();
        el.classList.remove('dropDown-top');
        if(needToMoveOnTop(el)) {
            el.top = newTopValue;
            el.right = newRightValue;
            el.classList.add('dropDown-top');
        }
    },
    render() {
        let dataFeed = this.props.dataFeed;
        return (
            <DropDown >
                {dataFeed.map((data, i) => {
                    return (<DropDownRow key={response.symbol} data={data}/>);
                })}
            </DropDown>
        );
    }
});

这里是setstate的代码(创建一个无限循环)

let SearchDropdown = React.createClass({
    getInitialState() {
        return {
            top: false
        };
    },
    componentDidUpdate(params) {
        let el = this.getDOMNode();
        if (this.state.top) {
           this.setState({top: false});
        }
        if(needToMoveOnTop(el)) {
            el.top = newTopValue;
            el.right = newRightValue;
            if (!this.state.top) {
              this.setState({top: true});
           }
        }
    },
    render() {
        let dataFeed = this.props.dataFeed;
        let class = cx({'dropDown-top' : this.state.top});
        return (
            <DropDown className={class} >
                {dataFeed.map((data, i) => {
                    return (<DropDownRow key={response.symbol} data={data}/>);
                })}
            </DropDown>
        );
    }
});

Answer 1

你可以setState在里面使用componentDidUpdate.问题是,你创建一个无限循环,因为没有中断条件.

基于以下事实:一旦呈现组件,您需要浏览器提供的值,我认为您使用的方法componentDidUpdate是正确的,它只需要更好地处理触发的条件setState.

Answer 2

如果你setState在里面使用componentDidUpdate它更新组件,导致一个调用componentDidUpdate,随后setState再次调用导致无限循环.您应该有条件地呼叫setState并确保最终发生违反呼叫的情况,例如:

componentDidUpdate: function() {
    if (condition) {
        this.setState({..})
    } else {
        //do something else
    }
}

如果你只是通过向它发送道具来更新组件(它没有被setState更新,除了componentDidUpdate中的情况),你可以调用setStateinside componentWillReceiveProps而不是componentDidUpdate.

Answer 3

该componentDidUpdate签名void::componentDidUpdate(previousProps, previousState).有了这个,您将能够测试哪些道具/状态是脏的,并相应地调用setState.

例:

componentDidUpdate(previousProps, previousState) {
    if (previousProps.data !== this.props.data) {
        this.setState({/*....*/})
    }
}

Answer 4

这个例子将帮助你理解React Life Cycle Hooks。

您可以setState在getDerivedStateFromProps方法 ie 中static并在道具更改后触发方法componentDidUpdate。

在componentDidUpdate您将获得3 PARAM从返回getSnapshotBeforeUpdate。

您可以检查此代码和框链接

// Child component
class Child extends React.Component {
  // First thing called when component loaded
  constructor(props) {
    console.log("constructor");
    super(props);
    this.state = {
      value: this.props.value,
      color: "green"
    };
  }

  // static method
  // dont have access of 'this'
  // return object will update the state
  static getDerivedStateFromProps(props, state) {
    console.log("getDerivedStateFromProps");
    return {
      value: props.value,
      color: props.value % 2 === 0 ? "green" : "red"
    };
  }

  // skip render if return false
  shouldComponentUpdate(nextProps, nextState) {
    console.log("shouldComponentUpdate");
    // return nextState.color !== this.state.color;
    return true;
  }

  // In between before real DOM updates (pre-commit)
  // has access of 'this'
  // return object will be captured in componentDidUpdate
  getSnapshotBeforeUpdate(prevProps, prevState) {
    console.log("getSnapshotBeforeUpdate");
    return { oldValue: prevState.value };
  }

  // Calls after component updated
  // has access of previous state and props with snapshot
  // Can call methods here
  // setState inside this will cause infinite loop
  componentDidUpdate(prevProps, prevState, snapshot) {
    console.log("componentDidUpdate: ", prevProps, prevState, snapshot);
  }

  static getDerivedStateFromError(error) {
    console.log("getDerivedStateFromError");
    return { hasError: true };
  }

  componentDidCatch(error, info) {
    console.log("componentDidCatch: ", error, info);
  }

  // After component mount
  // Good place to start AJAX call and initial state
  componentDidMount() {
    console.log("componentDidMount");
    this.makeAjaxCall();
  }

  makeAjaxCall() {
    console.log("makeAjaxCall");
  }

  onClick() {
    console.log("state: ", this.state);
  }

  render() {
    return (
      <div style={{ border: "1px solid red", padding: "0px 10px 10px 10px" }}>
        <p style={{ color: this.state.color }}>Color: {this.state.color}</p>
        <button onClick={() => this.onClick()}>{this.props.value}</button>
      </div>
    );
  }
}

// Parent component
class Parent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { value: 1 };

    this.tick = () => {
      this.setState({
        date: new Date(),
        value: this.state.value + 1
      });
    };
  }

  componentDidMount() {
    setTimeout(this.tick, 2000);
  }

  render() {
    return (
      <div style={{ border: "1px solid blue", padding: "0px 10px 10px 10px" }}>
        <p>Parent</p>
        <Child value={this.state.value} />
      </div>
    );
  }
}

function App() {
  return (
    <React.Fragment>
      <Parent />
    </React.Fragment>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>