Redux reducers 初始化相同的状态键

Question

我在摆弄 'simplest-redux-example' on github，我添加了第二个递减 state.count 的减速器。如果我在 switch case 语句中有增量和减量缩减器，它工作正常。我想要执行的练习是将 reducer 拆分为尽可能多的模块化部分。此代码抛出一个错误，指出计数未定义。

import React from 'react';
import { createStore, combineReducers } from 'redux';
import { Provider, connect } from 'react-redux';

// React component
class Counter extends React.Component {
  render(){
    const { value, onIncreaseClick, onDecreaseClick } = this.props;
    return (
      <div>
        <span>{value}</span>
        <button onClick={onIncreaseClick}>Increase</button>
        <button onClick={onDecreaseClick}>Decrease</button>
      </div>
    );
  }
}

// Action:
const increaseAction = {type: 'increase'};
const decreaseAction = {type: 'decrease'};

// Reducer:
function counter(state, action) {
  let count = state.count;
  switch(action.type){
    case 'increase':
      return {count: count+1};
    default:
      return state;
  }
}
function decrementer(state, action) {
  let count = state.count;
  switch(action.type){
    case 'decrease':
      return {count: count -1};
    default:
      return state;
  }
}
const rootReducer = combineReducers({
  counter,
  decrementer
})

// Store:
let store = createStore(rootReducer, {count: 0});

// Map Redux state to component props
function mapStateToProps(state)  {
  console.log("mapStatetoProps heyyyy");
  return {
    value: state.count
  };
}

// Map Redux actions to component props
function mapDispatchToProps(dispatch) {
  console.log("mapDispatchtoProps heyyyy");
  return {
    onIncreaseClick: () => dispatch(increaseAction),
    onDecreaseClick: () => dispatch(decreaseAction)
  };
}

// Connected Component:
let App = connect(
  mapStateToProps,
  mapDispatchToProps
)(Counter);

React.render(
  <Provider store={store}>
    {() => <App />}
  </Provider>,
  document.getElementById('root')
);

Answer 1

传递给 combineReducers 的 reducer 获得状态对象的不同部分。

The resulting reducer calls every child reducer, and gather their results into a single state object. The shape of the state object matches the keys of the passed reducers.

（强调我的）

所以，内部状态对象看起来像

{
  counter: result of passing `state.counter` into counter reducer
  decrementer: result of passing `state.decrementer` into decrementer reducer
}

这类似于在 flux 应用程序中拥有单独的商店，其中每个商店都操作自己的 "piece" 全局应用程序状态。

由于您实际上希望这两个 reducer 在状态对象的相同部分上工作，因此您实际上想要更像 reduce-reducers 的东西，尽管这很容易自己实现——只需将状态依次传递给每个 reducer，用来自每个 reducer 的新状态减少初始状态。

其实就这么简单，实现就几行：

export default function reduceReducers(...reducers) {
  return (previous, current) =>
    reducers.reduce(
      (p, r) => r(p, current),
      previous
    );
}

你的rootReducer会是

const rootReducer = reduceReducers(counter, decrementer);

Answer 2

你太接近了！问题在于，当您使用 combineReducers 时，它实际上会拆分 "state"，这样您输入的 reducer 的状态就是 "state" 对象的属性。

因此，为了给它们提供默认参数，如下所示： let store = createStore(rootReducer, {counter: {count: 0}, decrementer: {count:0}});

Redux reducers 初始化相同的状态键

Redux reducers initializing same state key

javascript

reactjs

redux