reactjs - mapStateToProps 不提供状态数据

Question

我有这个错误:

TypeError: Cannot read property 'map' of undefined

并且不知道如何this.props.movi​​es未定义，而我将initialState声明为[]，然后它必须直接去渲染？

所以有文件:

Reducer.js

import * as types from "./ActionTypes.js";

const initialState = { movies: [] };

export const reducer = (state = initialState, action) => {
  console.log(state.movies);
  switch (action.type) {
    case types.GET_MOVIES:
      return {
        ...state,
        movies: action.value
      };
    default:
      return state;
  }
};

电影.js

import React, { Component } from "react";
import { connect } from "react-redux";
import MovieItem from "./MovieItem";

const mapStateToProps = state => ({
  movies: state.movies
});

class Movies extends Component {
  render() {
    let movieItems = this.props.movies.map(movie => {
      return <MovieItem movie={movie} />;
    });
    return <div className="Movies">{movieItems}</div>;
  }
}

export default connect(mapStateToProps, null)(Movies);

即使我添加像这样的 if 语句

if (this.props.movies){
...
}else return 1;

它从不重新渲染

Answer 1

应该是:

const mapStateToProps = state => ({
    movies: state.reducer.movies
});

因为你的初始状态是一个对象:

initialState = { movies: [] };

并且您正在使用combineReducers，如下所示:

const rootReducer = combineReducers({ reducer: reducer }); 

现在，该 reducer 的所有 initialState 都可以通过 state.reducer.propertyName 访问。

注意:不要使用reducer，最好使用一些直观的名称，例如moviesReducer。稍后，如果您添加更多 reducer ，那么它将有助于识别数据。