如何使用 redux 为反应 js 设置加载 state

Question

i'm using redux and i want to show an loading state for my app whenever my app is catching data from api and whenever i have an data of null in my reducers
i've tried this but i got no loading text

    if (this.props.isSignedIn === true) {
      return <div
        style={{ textAlign: "right" }}>
        <Link to='/streams/new' className='ui button primary'>
          create new stream
      </Link>
      </div>
    }
    if (this.props.isSignedIn === false) {
      return <div style={{ fontSize: '30px' }}>Not a user? sign in now, it's free </div>
    }
    if (this.props.isSignedIn ===null) {
      <div>loading...</div>
    }
  }  

here is connect and mapstatetoprops function

const mapStateToProps = state => {
  return {
    streams: Object.values(state.streams),
    userId: state.auth.userId,
    isSignedIn: state.auth.isSignedIn
  };
};

export default connect(
  mapStateToProps,
  { fetchStreams }
)(StreamList);

and here is reducer

import { SIGN_IN, SIGN_OUT } from '../actions/types';

const INTIAL_STATE = {
  isSignedIn: null,
  userId: null
};

export default (state = INTIAL_STATE, action) => {
  switch (action.type) {
    case SIGN_IN:
      return { ...state, isSignedIn: true, userId: action.payload };
    case SIGN_OUT:
      return { ...state, isSignedIn: false, userId: null };
    default:
      return state;
  }
};

here is actions

export const signIn = userId => {
  return {
    type: SIGN_IN,
    payload: userId
  };
};

export const signOut = () => {
  return {
    type: SIGN_OUT
  };
};

NOTE:

in cases true and false works fine except for null

Answer 1

Usually it is done with setting 'loading' property on store and adding an additional action such as 'SIGN_INIT'

So your reducer will look like this:

const INTIAL_STATE = {
  isSignedIn: null,
  loading: false,
  userId: null
};


export default (state = INTIAL_STATE, action) => {
  switch (action.type) {
    case SIGN_INIT:
      return { ...state, loading: true };
    case SIGN_IN:
      return { ...state, isSignedIn: true, loading: false, userId: action.payload };
    case SIGN_OUT:
      return { ...state, isSignedIn: false, loading: false, userId: null };
    default:
      return state;
  }
};

So when you try to sign in or out, first you dispatch SIGN_INIT which sets 'loading' to true. Whenever request is finished SIGN_IN\SIGN_OUT actions will have your 'loading' prop updated in store and component will be notified that loading is finished.