5.1 Fetch

1.apply redux-thunk middleware

import { applyMiddleware, createStore, compose } from 'redux';
import thunk from 'redux-thunk';
import createLogger from 'redux-logger';
import reducers from '../reducers';

var middlewares = compose(applyMiddleware(thunk), autoRehydrate());

export default function configureStore() {
  const store = createStore(reducers, undefined, middlewares);
  return store;
}

2.start & end action types

//todo action types
export const START_FETCH_ALL_TODOS = 'START_FETCH_ALL_TODOS';
export const FETCH_ALL_TODOS = 'FETCH_ALL_TODOS';

3.fetch flow

import * as types from '../constants/ActionTypes';
import * as APIs from '../constants/ServerAPIs';


function shouldFetchAllTodos(state) {
  const data = state.todos;
  if (data && data.isFetchingAllTodos) {
    return false
  }
  return true;
}

export function fetchAllTodos() {
  return async (dispatch, getState) =>{
    //verify
    if(!shouldFetchAllTodos(getState())){
      return Promise.resolve();
    }

    //dispatch fetch start action
    dispatch({type: types.START_FETCH_ALL_TODOS});

    //fetching
    const response = await fetch(APIs.allTodos);
    //response
    const data = await response.json();

    //dispatch fetch end action
    return dispatch({
      type: types.FETCH_ALL_TODOS,
      data
    });
  }
}

4.reducer

export default function todos(state = initialState, action) {
  switch (action.type) {
    case types.START_FETCH_ALL_TODOS:
      return Object.assign({}, state, {isFetchingAllTodos: true});

    case types.FETCH_ALL_TODOS:
      return Object.assign({}, state, {
        isFetchingAllTodos: false,
        data: action.data.data.reduce(function (pre, cur) {
          //remove duplicates
          !pre.find( key=> key.id===cur.id) && pre.push(cur);
          return pre;
        }, [...state.data])
      });
    ...
    ...
    default:
      return state
  }
}

5.dispatch & render

...
  componentDidMount(){
    //fetch data from server
    this.props.actions.fetchAllTodos();
  }
...
...
  renderLoading = () => {
    if (this.props.todos.isFetchingAllTodos) {
      return (
        <View style={styles.loading}>
          <Text style={styles.loadingText}>Loading...</Text>
        </View>
      )
    }
    return null;
  }
...