您如何从另一个动作中的动作获得结果？答案

【问题标题】：How do you get the result from action in another action?您如何从另一个动作中的动作获得结果？
【发布时间】：2023-03-21 03:24:01
【问题描述】：

我是 dvajs 的新手。我正在使用 React 17,x, Typescript 4.2.3, antd 4.15.0, umi 3.4.7

问题。 如果我导航到 /s/ 页面，代码应该从 API 获取一些类别并向服务器发出另一个请求，此时在某些页面上显示它们。但是在调用搜索效果的那一刻，类别是空的，所以我尝试再次调用 getCategories 动作。但是类别仍然是空的。您如何从另一个动作中的动作获得结果？也许有某种调度链？

代码如下

import { fetchCategories, makeSearch } from '@/services/search';
import { CategoriesModelStateSelector, Subscription } from '@@/plugin-dva/connect';
import { Reducer, Effect } from 'umi';
export type SearchModelState = {
  searchResults: Provider[]
  categories: Category[]
}
export type SearchModelType = {
  namespace: string;
  state: SearchModelState;
  effects: {
    getCategories: Effect;
    search: Effect;
  };
  reducers: {
    setCategories: Reducer
    setSearchResults: Reducer
  };
  subscriptions: {
    setup: Subscription
  }
};
export type SearchModelStateSelector = {
  search: SearchModelState
};
const SearchModel: SearchModelType = {
  namespace: 'search',
  state: {
categories: [],
searchResults: [],
},      
effects: {
    * getCategories({ payload }, { call, put, select }) {
      const response = yield call(fetchCategories);
  if (response) {
    yield put({
      type: 'setCategories',
      payload: response,
    });
  }
},
* search({ payload }, { call, put, select }) {
  let categories = yield select(({ categories: state }: CategoriesModelStateSelector) => state.categories);
  // HERE categories are empty
  console.log(categories);
  yield put({
    type: 'getCategories',
    payload: {},
  });

  let catss = yield select(({ categories: state }: CategoriesModelStateSelector) => state.categories);
  console.log(catss);
  // HERE categories are still empty

  const response = yield call(makeSearch, payload);
  yield put({
    type: 'setSearchResults',
    payload: response,
  });
},
},


    reducers: {
        setCategories(state, { payload }) {
          return {
            ...state,
            categories: response,
      };
    },
    setSearchResults(state, { payload }) {
      return {
        ...state,
        searchResults: response,
      };
    },
  },
  subscriptions: {
    setup({ dispatch, history }) {
      // @ts-ignore
      return history.listen(({ pathname, query }) => {
        dispatch({ type: 'getCategories', payload: {} });

        if (pathname === '/s' || pathname === '/s/') {
          dispatch({ type: 'search', payload: query });
        }
      });
    },
  },
};

export default SearchModel;

【问题讨论】：

标签： redux-saga umijs dvajs

【解决方案1】：

建议的解决方案：

yield put({
    type: 'getCategories',
    payload: {},
  });

// something like this will wait until CATEGORIES_WERE_FETCHED was dispatched on 
// the store, before continuing to next line: 'take' is what you are looking for
yield take("CATEGORIES_WERE_FETCHED")

let catss = yield select(

Redux-Saga 采取：创建一个 Effect 描述，指示中间件等待 Store 上的指定操作。生成器被挂起，直到调度匹配模式的操作。

https://redux-saga.js.org/docs/api/

我又看了你的代码：

yield put({
      type: 'setCategories',
      payload: response,
    });

您正在使用 'setCategories' 操作，因此您可以使用 take('setCategories') - 如果您想“等待”直到某个操作被分派，就像上面的方式一样。

【讨论】：