从componentdidmount访问calculatestate内部的状态

Question

我不熟悉助焊剂并起反应，我想知道如何从componentdidmount（）？

如何访问componentdidmount（）中的事件状态？我想循环浏览事件，然后针对每个事件运行查询，这反过来又更新了另一个商店。

static getStores() {
  return [SomeStore];
}
static calculateState(prevState, props) {
  const somestore = SomeStore.getState();

  return {
    events: SomeStore.getState(),
  };
}

componentdidmount(){

  //this.state.events;
  //need to do some query based on the events
  //this query will update another store.
}

Answer 1

您需要使用生命周期方法来了解componentDidMount概述的here方法>

要初始化localstate，您应该使用构造函数方法（也可以使用static方法，但是jsfiddle会引发错误。

要显示初始状态，可以在componentDidMount中使用this.state登录。

const someStore = ["event"];

class TodoApp extends React.Component {
  constructor(props) {
    super(props);
    this.state = { events: someStore };
  }

  // if you want to change state based on props
  shouldComponentUpdate(nextProps, nextState) {
    // change state if you want here
    if (this.state.events.length !== nextState.events.length) {
      console.log(this.state, nextState)
      return true // update
    }

    return false
  }

  // get initial state
  componentDidMount() {
    console.log(this.state.events);
  }

  render() {
    return (
      <div>
        <span>example</span>
        <button onClick = {() => {
          this.setState(state => {
            return {
              events: [...state.events, "new event"]
            }
          })
        }}>Add Event</button>
        
        <div>
          events: { JSON.stringify(this.state.events) }
        </div>
      </div>
    )
  }
}

ReactDOM.render(<TodoApp />, document.querySelector("#app"));
body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#app {
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  transition: all 0.2s;
}
<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>
<div id="app"></div>