如何在 React Redux 应用程序中显示加载指示器，同时获取数据？

You can add change listeners to your stores, using either connect() from React Redux or the low-level store.subscribe() method. You should have the loading indicator in your store, which the store change handler can then check and update the component state. The component then renders the preloader if needed, based on the state.

alert and confirm shouldn't be a problem. They are blocking and alert doesn't even take any input from the user. With confirm, you can set state based on what the user has clicked if the user choice should affect component rendering. If not, you can store the choice as component member variable for later use.

I mean they are more like events than state!

I would not say so. I think loading indicators are a great case of UI that is easily described as a function of state: in this case, of a boolean variable. While this answer is correct, I would like to provide some code to go along with it.

In the async example in Redux repo, reducer updates a field called isFetching:

case REQUEST_POSTS:
return Object.assign({}, state, {
isFetching: true,
didInvalidate: false
})
case RECEIVE_POSTS:
return Object.assign({}, state, {
isFetching: false,
didInvalidate: false,
items: action.posts,
lastUpdated: action.receivedAt

The component uses connect() from React Redux to subscribe to the store’s state and returns ABC1 as part of the mapStateToProps() return value so it is available in the connected component’s props:

function mapStateToProps(state) {
const { selectedReddit, postsByReddit } = state
const {
isFetching,
lastUpdated,
items: posts
} = postsByReddit[selectedReddit] || {
isFetching: true,
items: []
}


return {
selectedReddit,
posts,
isFetching,
lastUpdated
}
}

Finally, the component uses ABC0 prop in the render() function to render a “Loading...” label (which could conceivably be a spinner instead):

{isEmpty
? (isFetching ? <h2>Loading...</h2> : <h2>Empty.</h2>)
: <div style=\{\{ opacity: isFetching ? 0.5 : 1 }}>
<Posts posts={posts} />
</div>
}

Even a worse case, what should I do when I have to use the native confirm dialog or alert dialog in redux/react apps? Where should they be put, actions or reducers?

Any side effects (and showing a dialog is most certainly a side effect) do not belong in reducers. Think of reducers as passive “builders of state”. They don’t really “do” things.

If you wish to show an alert, either do this from a component before dispatching an action, or do this from an action creator. By the time an action is dispatched, it is too late to perform side effects in response to it.

For every rule, there is an exception. Sometimes your side effect logic is so complicated you actually want to couple them either to specific action types or to specific reducers. In this case check out advanced projects like Redux Saga and Redux Loop. Only do this when you are comfortable with vanilla Redux and have a real problem of scattered side effects you’d like to make more manageable.

I'd like to add something. The real world example uses a field isFetching in the store to represent when a collection of items is being fetched. Any collection is generalized to a pagination reducer that can be connected to your components to track the state and show if a collection is loading.

It happened to me that I wanted to fetch details for an specific entity that doesn't fit in the pagination pattern. I wanted to have a state representing if the details are being fetched from the server but also I didn't want to have a reducer just for that.

To solve this I added another generic reducer called fetching. It works in a similar fashion to the pagination reducer and it's responsibility is just to watch a set of actions and generate new state with pairs [entity, isFetching]. That allows to connect the reducer to any component and to know if the app is currently fetching data not just for a collection but for an specific entity.

Great answer Dan Abramov! Just want to add that I was doing more or less exactly that in one of my apps (keeping isFetching as a boolean) and ended up having to make it an integer (which ends up reading as the number of outstanding requests) to support multiple simultaneous requests.

with boolean:

request 1 starts -> spinner on -> request 2 starts -> request 1 ends -> spinner off -> request 2 ends

with integer:

request 1 starts -> spinner on -> request 2 starts -> request 1 ends -> request 2 ends -> spinner off

case REQUEST_POSTS:
return Object.assign({}, state, {
isFetching: state.isFetching + 1,
didInvalidate: false
})
case RECEIVE_POSTS:
return Object.assign({}, state, {
isFetching: state.isFetching - 1,
didInvalidate: false,
items: action.posts,
lastUpdated: action.receivedAt

We have three types of notifications in our app, all of which are designed as aspects:

1. Loading indicator (modal or non-modal based on prop)
2. Error Popup (modal)
3. Notification snackbar (non-modal, self closing)

All three of these are at the top level of our app (Main), and wired through Redux as shown in the below code snippet. These props control display of their corresponding aspects.

I designed a proxy that handles all our API calls, thus all isFetching and (api) errors are mediated with actionCreators I import in the proxy. (As an aside, I also use webpack to inject a mock of the backing service for dev so we can work without server dependencies.)

Any other place in the app that needs to provide any type of notification simply imports the appropriate action. Snackbar & Error have params for messages to be displayed.

@connect(
// map state to props
state => ({
isFetching      :state.main.get('isFetching'),   // ProgressIndicator
notification    :state.main.get('notification'), // Snackbar
error           :state.main.get('error')         // ErrorPopup
}),
// mapDispatchToProps
(dispatch) => { return {
actions: bindActionCreators(actionCreators, dispatch)
}}

) export default class Main extends React.Component{

I didn't happen upon this question until now, but since no answer is accepted I'll throw in my hat. I wrote a tool for this very job: react-loader-factory. It's got slightly more going on than Abramov's solution, but is more modular and convenient, since I didn't want to have to think after I wrote it.

There are four big pieces:

• Factory pattern: This allows you to quickly call the same function to set up which states mean "Loading" for your component, and which actions to dispatch. (This assumes that the component is responsible for starting the actions it waits on.) const loaderWrapper = loaderFactory(actionsList, monitoredStates);
• Wrapper: The component the Factory produces is a "higher order component" (like what connect() returns in Redux), so that you can just bolt it onto your existing stuff. const LoadingChild = loaderWrapper(ChildComponent);
• Action/Reducer interaction: The wrapper checks to see if a reducer it's plugged into contains keywords that tell it not to pass through to the component that needs data. The actions dispatched by the wrapper are expected to produce the associated keywords (the way redux-api-middleware dispatches ACTION_SUCCESS and ACTION_REQUEST, for example). (You could dispatch actions elsewhere and just monitor from the wrapper if you wanted, of course.)
• Throbber: The component you want to appear while the data your component depends on isn't ready. I added a little div in there so you can test it out without having to rig it up.

The module itself is independent of redux-api-middleware, but that's what I use it with, so here's some sample code from the README:

A component with a Loader wrapping it:

import React from 'react';
import { myAsyncAction } from '../actions';
import loaderFactory from 'react-loader-factory';
import ChildComponent from './ChildComponent';


const actionsList = [myAsyncAction()];
const monitoredStates = ['ASYNC_REQUEST'];
const loaderWrapper = loaderFactory(actionsList, monitoredStates);


const LoadingChild = loaderWrapper(ChildComponent);


const containingComponent = props => {
// Do whatever you need to do with your usual containing component


const childProps = { someProps: 'props' };


return <LoadingChild { ...childProps } />;
}

A reducer for the Loader to monitor (although you can wire it differently if you want):

export function activeRequests(state = [], action) {
const newState = state.slice();


// regex that tests for an API action string ending with _REQUEST
const reqReg = new RegExp(/^[A-Z]+\_REQUEST$/g);
// regex that tests for a API action string ending with _SUCCESS
const sucReg = new RegExp(/^[A-Z]+\_SUCCESS$/g);


// if a _REQUEST comes in, add it to the activeRequests list
if (reqReg.test(action.type)) {
newState.push(action.type);
}


// if a _SUCCESS comes in, delete its corresponding _REQUEST
if (sucReg.test(action.type)) {
const reqType = action.type.split('_')[0].concat('_REQUEST');
const deleteInd = state.indexOf(reqType);


if (deleteInd !== -1) {
newState.splice(deleteInd, 1);
}
}


return newState;
}

I expect in the near future I'll add things like timeout and error to the module, but the pattern's not going to be very different.

The short answer to your question is:

1. Tie rendering to rendering code--use a wrapper around the component you need to render with the data like the one I showed above.
2. Add a reducer that makes the status of requests around the app you might care about easily digestible, so you don't have to think too hard about what is happening.
3. Events and state aren't really different.
4. The rest of your intuitions seem correct to me.

Am I the only one thinking that loading indicators don't belong in a Redux store? I mean, I don't think it's part of an application's state per se..

Now, I work with Angular2, and what I do is that I have a "Loading" service which exposes different loading indicators via RxJS BehaviourSubjects.. I guess the mechanism is the same, I just don't store the information in Redux.

Users of the LoadingService just subscribe to those events they want to listen to..

My Redux action creators call the LoadingService whenever things need to change. UX components subscribe to the exposed observables...

I'm saving the urls such as::

isFetching: {
/api/posts/1: true,
api/posts/3: false,
api/search?q=322: true,
}

And then I have a memorised selector (via reselect).

const getIsFetching = createSelector(
state => state.isFetching,
items => items => Object.keys(items).filter(item => items[item] === true).length > 0 ? true : false
);

To make the url unique in case of POST, I pass some variable as query.

And where I want to show an indicator, I simply use the getFetchCount variable