javascript - 我的 ReactJS 组件怎么可能在旧状态和新状态之间交替？

Question

我在 render() 函数中放置了一个 console.log。

我在函数内部使用 setState()。然后我的组件更新，但紧接着我可以检查状态是否恢复到旧状态。

编辑:现在我的问题是在扩展时正确显示状态，我认为其余的工作正常。

这是我的沙盒: https://codesandbox.io/s/77ymmnpr1

在我的代码中，我创建了三个可扩展的标签，然后我放置了一些 labelComponent 来覆盖它们。叠加层有一个按钮可以返回菜单。问题是，当我随后展开另一个 labelComponent 时，旧状态与显示新状态之间存在轻微的滞后。因此，我向您提供了 console.log。

在控制台中放置如下内容:

PATHNAME: newState
PATHNAME: oldState
PATHNAME: newState
PATHNAME: oldState

编辑:现在我的控制台在第二次渲染时返回:

stateOne

currentState

然后，在第三次渲染时:

stateOne

stateTwo

currentState

第四次渲染:

stateOne

stateTwo

stateThree

currentState

这是什么意思？我调用 this.setState() 只是为了将新状态放入其中，那么为什么它又回到旧状态呢？

这是我的 react.js 代码:

export default class Label extends Component {

  state={ 
    labelStock:[],

    sequence:undefined,
    labelToRemove:[],
    pathname:"",
    displayLabel:false,

    displayFreshFood:false,
    displayLocalFarm:false,
    displayBeerQuality:false
  }

  componentDidMount(){   
      this.setLabelArray()
  }

  shouldComponentUpdate(nextProps, nextState) {  
    let {pathname}= nextState   
    console.log("NEXTSTATE: ", pathname) 
    if(this.state.pathname !== nextState.pathname){ 
        if((
          pathname.includes("freshfood") ||
          pathname.includes("localfarm") ||
          pathname.includes("beerquality") ) && this.state.labelToRemove.length >0
          ){  
            this.setState({displayLabel:true})
          }
          else if(this.state.displayLabel !== nextState.displayLabel){ 
            this.setState({displayLabel:false})            
          }  

          return true
    }    
    else if(this.state.displayLabel !== nextState.displayLabel){ 
        return true 
    }

    return false
  }
  setLabelArray=()=>{ 
    let labelArray=[]

    labelStock.forEach(function (item) {
      labelArray.push(item.name);
    });

    this.setState({labelStock:labelArray})
  }

  renderLabel=()=>(
    labelStock.map((item, index) =>{

      return ( 
        <div 
          ref={item.name}
          key={index}
          style={{backgroundImage: `url(${item.image})`}}
          className={this.state.labelToRemove.includes(item.name) ? `${style.label_container} ${style.label_to_remove}` : style.label_container}
        >
          <div  
          style={{display: this.state.displayLabel ? 'none' : 'initial' }}
          onClick={() => this.expand(item.name)} 
          className={style.more_info_button}> 
              <img  src={moreInfoButton} alt=""/> 
          </div>
          <div id={style.label_item} > Here some text</div>
        </div>
      )
  })
)

  expand=(item)=>{ 

    console.log("IN EXPAND")
    let removeItem= this.state.labelStock.filter(word => word!== item);
    this.setState({
      labelToRemove:removeItem,
      displayLabel:true,
      pathname:""
    })
    let [removeOne, removeTwo]= removeItem 
    let removeOneStyle=this.refs[removeOne].style;
    let removeTwoStyle=this.refs[removeTwo].style;

    removeOneStyle.opacity="0";
    removeTwoStyle.opacity="0";
    removeOneStyle.top="-20%";
    removeTwoStyle.top="-20%";

    setTimeout(function(){ 
      removeOneStyle.width="0vw";
      removeTwoStyle.width="0vw";

    }, 750);

    removeOneStyle.visibility="hidden";
    removeTwoStyle.visibility="hidden";

    let itemStyle= this.refs[item].style
    let layoutStyle=this.refs.layout.style
    layoutStyle.padding="0";
    layoutStyle.gridColumnGap="0";


    this.refs[item].addEventListener('transitionend', (e)=> {
      // let label= item.toLowerCase()
      // this.setState({pathname:label})
      if(e.propertyName !=="width") return 
      setTimeout(() => {  
        let updatedPathname= "label/" + item.toLowerCase(); 
        let label= item.toLowerCase()
        if(e.propertyName ==="width") this.setState({pathname:label})
      }, 1000);
    }); item

    itemStyle.height= 100+"vh";
    itemStyle.width= 100+"vw";    
    itemStyle.zIndex="100";     
  } 


  menuBack=()=>{  
    this.setState({
      displayLabel:false,
      labelToRemove:""
    })

    let item = this.state.pathname

    let enterItem= this.state.labelStock.filter(word => word!== item);
    // this.setState({

    // })
    let [enterOne, enterTwo]= enterItem
    // console.log("removeOne, removeTwo: ", removeOne, removeTwo)
    let enterOneStyle=this.refs[enterOne].style;
    let enterTwoStyle=this.refs[enterTwo].style;

    enterOneStyle.opacity="1";
    enterTwoStyle.opacity="1";

    enterOneStyle.top="0%";
    enterTwoStyle.top="0%";

    setTimeout(function(){ 
      enterOneStyle.width="25vw";
      enterTwoStyle.width="25vw";

    }, 750);

    enterOneStyle.visibility="visible";
    enterTwoStyle.visibility="visible";

    let itemStyle= this.refs[item].style
    let layoutStyle=this.refs.layout.style
    layoutStyle.padding="0 1vw";
    layoutStyle.gridColumnGap="1.5vw";

    itemStyle.height= "50vh";
    itemStyle.width= "25vw";    
    itemStyle.zIndex="10";  
    this.setState({pathname:""})
  }

  render() { 
    var hiddenStyle={ visiblity:"hidden"};
    var displayStyle={display:"inline-block"};
    var displayFreshFood = this.state.pathname.includes("freshfood") && this.state.displayLabel
    var displayBeerQuality = this.state.pathname.includes("beerquality") && this.state.displayLabel
    var displayLocalFarm= this.state.pathname.includes("localfarm") && this.state.displayLabel

    console.log("PATHNAME: "+ this.state.pathname) 
          return (
            <div
              className={style.page}
            >             

              <div
                ref="freshfood"
                className={style.label_content}
                style={{display: this.state.pathname.includes("freshfood") && this.state.displayLabel ? 'block' : 'none' }}
              >              
                <FreshFood/>
              </div>

              <div
                ref="localfarm"
                className={style.label_content}
                style={{display: this.state.pathname.includes("localfarm") && this.state.displayLabel ? 'block' : 'none' }}
              >  
                <LocalFarm/>
              </div>

              <div
                ref="beerquality"
                className={style.label_content}
                style={{display: this.state.pathname.includes("beerquality") && this.state.displayLabel ? 'block' : 'none' }}
              >  
                <BeerQuality
                  style= {this.state.displayBeerQuality? 
                  displayStyle: hiddenStyle}
                />
               </div>

              <div
                        className={style.label_background}
                                style={{opacity: this.state.displayLabel ? 0.5: 1 }}

              >
                <div
                  id={style.presentation_video}
                > 
                <video 
                  autoPlay="autolay" 
                  muted
                  loop        
                  controls
                >
                    <source src={goldLightVideo} type="video/mp4"/>
                    <source src={goldLightVideo} type="video/ogg"/>
                    error: video module fails to display
                </video>        
                </div>
                <div 
                  ref="layout"
                  className={style.label_layout}
                >
                    {this.renderLabel()}
                </div>
              </div>      
            <BackButton
              className={style.back_button}
              visible={this.state.displayLabel}
              onClick={this.menuBack}
            >
              <img id={style.back_button_icon} src={backButtonIcon} alt=""/>
            </BackButton>
      </div> 
      )


  }
}

任何提示都会很棒，谢谢

Answer 1

您正在为 transitionend 事件添加一个事件监听器，它会在超时后设置状态。但是，您永远不会删除该监听器，因此每次您在 DOM 中操作元素转换时都会调用它，这基本上是在每个单击事件上发生的。您可以通过在 transitionend 事件监听器完成它的工作后(即在它设置状态之后)删除它来解决这个问题。以下代码应放在您的扩展函数中，替换您的 this.refs[item].addEventListener(...) 逻辑:

this.addTransitionListener = listener.bind(this);
function listener(e) {
  // let label= item.toLowerCase()
  // this.setState({pathname:label})
  if (e.propertyName !== "width") return
  setTimeout(() => {
    if (e.propertyName === "width") {
      let updatedPathname = "label/" + item.toLowerCase();
      let label = item.toLowerCase()
      this.setState({
        pathname: label,
        displayLabel: true
      }, () => {
        console.log('removing listener')
        this.refs[item].removeEventListener('transitionend', this.addTransitionListener)
      })
    }
  }, 1000);
}
this.refs[item].addEventListener('transitionend', this.addTransitionListener);

可以在此处找到带有更改的代码分支:https://codesandbox.io/s/34klvpyw9p