Question

我有一个列表，用户可以向其中添加项目。然后，用户可以“喜欢”列表中的任何项目，并且在该项目上显示喜欢的次数。但是，当我在某个项目上单击“喜欢”时，整个列表将消失。组件的状态具有所有正确的，更新的数据，因此我认为问题可能与组件渲染太早有关。状态更新后，如何确保组件（Category.jsx）重新正确显示？

App.js（父组件）

class App extends Component {
  state = {
    wentWell: [],
    wellValue: '',
  }

  updateWellValue = e => this.setState({ wellValue: e.target.value });

  wellSubmit = e => {
    e.preventDefault();
    this.setState({
      wentWell: [...this.state.wentWell, {value: this.state.wellValue, likes: 0, dislikes: 0}],
      wellValue: ''
    })
  }

wellUpvote = upvoteIndex => {
    const wentWell = Object.assign({}, this.state.wentWell);
    wentWell[upvoteIndex].likes += 1;
    return this.setState({ wentWell });
  }  


  render() {
    return (
      <>
        <Title />
        <div className="container">
          <Category 
            name="Went Well" 
            items={this.state.wentWell}
            inputValue={this.state.wellValue}
            updateInput={this.updateWellValue}
            submit={this.wellSubmit}
            upvote={this.wellUpvote}
          />

</>
    );
  }
}

Category.jsx（子组件）

class Category extends Component {
  state = {
    items: this.props.items
  }

  static getDerivedStateFromProps(nextProps, prevState) {
    if(nextProps.items !== prevState.items){
      return ({ items: nextProps.items }) // <- this is setState equivalent
    }
  }

render() {
    return (
      <div className="category">
        <h2>{this.props.name}</h2>

        {/* ------ FORM (INPUT AND SUBMIT BUTTON) ------ */}
        <form onSubmit={e => this.props.submit(e)}>
          <input 
            placeholder="Enter note here"
            value={this.props.inputValue} 
            onChange={e => this.props.updateInput(e)}
          />
          <button type="submit" className={this.props.colorId}>Submit</button>
        </form> 

        {/* ------ MAPPED OUT ITEMS ------ */}
        {this.state.items.length > 0 ? 
          this.state.items.map((item, index) => {
            return (<Item 
              key={`item-${index}`} 
              index={index}
              upvote={this.props.upvote}
              item={item}
            />);
          }) : <h3>(Nothing here)</h3>
        }
      </div>
    )
  }
}

export default Category;

Answer 1

好像您正在尝试在数组上使用Object.assign。

const wentWell = Object.assign({}, this.state.wentWell);

尝试做

const tempWentWell = [...this.state.wentWell]

状态更改后重新渲染将返回空白

1 个答案: