componentDidUpdate 不使用 Redux 更新状态

Question

这个应用程序的目标是让我们使用React-Redux 和React Navigation 在列表项目屏幕中的Flatlist 中添加一个项目。基本上，我在 Create Item 屏幕中输入名称和类别，然后使用 React Navigation 以数组的形式将其发送到 List Item 屏幕，一旦进入 List Item 屏幕，我就使用 componentDidMount 来调度操作和更新类组件中的状态，问题是什么都没有显示，即使使用 console.log 它只会让我返回 Redux Reducers 屏幕中存在的空数组。

创建项目屏幕

export class item extends Component {
  constructor(props) {
    super(props);
    this.state = {
      name: '',
      category: '',
        };
  }



  submitItem = (name, category) => {
    this.props.navigation.navigate("ListItem", {
      itemList: {
    name: name,
    category: category,
   }});

  };


  

  render() {
    const { name, category } = this.state;
    return (
      <Container>
        <Header>
          <Left>
            <Button onPress={() =>
              this.submitItem(
                this.state.name,
                this.state.category,
              )
            }>
                <Text>Sumbit</Text>
            </Button>

项目列表屏幕

class ListItem extends Component {
  constructor(props) {
    super(props);
    this.state = {
      itemList:[],
    };
  }

  componentDidMount (props, state) {
    if (this.props.route.params?.itemList) {
      () => this.props.dispatch({type:'ADD_ITEM'});
    }
    return null;
  }

REDUX 减速器

const initialState = {
  currentUser: null,
  itemList: [],
};

export const user = (state = initialState, action) => {
  switch (action.type){
      case USER_STATE_CHANGE:
        return {
          ...state,
          currentUser: action.currentUser,
        };
      case 'ADD_ITEM': 
      return{
        itemList: state.itemList,
      }
      default:
        return state
  }
  
};

Answer 1

我认为，当您调度一个动作时，您并没有将 action.payload 添加到 state.itemList。我的意思是什么

const initialState = {
  currentUser: null,
  itemList: [],
};

export const user = (state = initialState, action) => {
  switch (action.type){
      case USER_STATE_CHANGE:
        return {
          ...state,
          currentUser: action.currentUser,
        };
      case 'ADD_ITEM': 
      return{
        ...state,
        itemList: addItemToList(state.itemList,action.payload), //a util function to add items to the list. 
// And action.payload is the value ,which passed when you are dispatching the action 'ADD_ITEM'
      }
      default:
        return state
  }
  
};

当您发送操作时，它应该是

componentDidMount (props, state) {
    if (this.props.route.params?.itemList) {
      () => this.props.dispatch({type:'ADD_ITEM',payload:this.props.route.params.itemList}); 
// passing the itemList to as the payload of the action.

    }
    return null;
  }

我想这个修改应该足够了。更多关于 React-Redux here