I want to use the useSelector() hook but I'm getting the error mentioned above. Where can I use this hook to get access to my state data?
function RetrieveDataSources() {
var dataSources = useSelector(state => state.dataSourcesReducer);
console.log(dataSources);
}
class Data extends Component {
constructor(props) {
super(props);
this.state = {
errorMessage: false,
isLoading: true,
resultData: propsState && propsState.resultData,
};
RetrieveDataSources();
}
render() {
return( some return code );
}
}
export default Data;
Hooks can only be called in either a function component, or custom hooks.
You are calling it from a normal function instead hence the error.
Furthermore, it seems you want to call a hook from a class component - that's unfortunately not directly supported. If you have to use class components, consider using mapStateToProps & connect apis instead to get it from your redux store.
If you still prefer to use hooks from within class component, here is an example to use function component and React render props to share it back with the parent component. This is usually done by libraries though where people cannot dictate whether the caller is using function component or class component.
I'm new to React and still struggling in understanding in using redux with React.
For example, below is some code :
const mapStateToProps = (storeData) => ({
editing: storeData.isEditMode;
})
const mapDispatchToProps = {
saveCallback: xxx
}
const connectFunction = connect(mapStateToProps, mapDispatchToProps);
export const ProductDisplay = connectFunction(
class extends Component {
render() {
if (this.props.editing) {
...
} else {
...
}
}
}
)
and a component that uses ProductDisplay
export default class App extends Component {
render() {
return <ProductDisplay/>
}
}
Let's say storeData.isEditMode is changed by other component, so the wrapped component's props.editing is changed. As we know that the only way to trigger update process is to use setState() but how does react know that ProductDisplay component needs to be updated since there is no setState() method involved?
The connect function generates a wrapper component that subscribes to the store. When an action is dispatched, the wrapper component's callback is notified. It then runs your mapState function, and shallow-compares the result object from this time vs the result object from last time (so if you were to rewrite a redux store field with its same value, it would not trigger a re-render). If the results are different, then it passes the results to your "real" component" as props.
Dan Abramov wrote a great simplified version of connect at (connect.js) that illustrates the basic idea, although it doesn't show any of the optimization work.
update
React-Redux v6.0.0 made some major internal changes to how connected components receive their data from the store.
For more details: https://spin.atomicobject.com/2018/04/02/redux-rerendering/
I'm working in a codebase that has a bunch of redux already working for managing and persisting state, as well as dispatching actions. My goal with the new Context API is to get rid of the prop-drilling that I have to do to deliver all these pieces of state to various components but keep the existing code for managing state in redux.
Now I've removed the excessive prop drilling code and replaced them with context Providers and Consumers, hooking them up in my components in all the right places. I'm still dispatching actions to redux and getting API responses populating my redux store, and I want to somehow notify the contexts to update when specific parts of the redux store update.
How do I get updates from the redux store delivered into my different Providers?
Since you are using the new Context Api, you can easily connect the component that uses the Context Provider with redux store and update the context values like
const Context = React.createContext();
class App extends React.Component {
state = {
user: ''
}
static getDerivedStateFromProps(nextProps, prevState) {
if(nextProps.user !== prevState.user) {
return {user: nextProps.user}
}
return null;
}
render() {
return <Context.Provider value={this.state.user}>
<MyComponent />
</Context.Provider>
}
}
const mapStateToProps(state) {
return {
user: state.user
}
}
export default connect(mapStateToProps)(App);
I'm still new to react/redux, after getting something like this to function
User.js
class User extends React.Component {
componentWillMount() {
this.props.fetchUser(.....);
}
render() {
return (
<Profile />
)
}
export default connect(null, {fetchUser})(User);
Profile.js
class Profile extends React.Component {
render() {
const { user } = this.props
return (
<h1>{user.profile.name}</h1>
)
}
const mapStateToProps = state => ({
user: state.store.user
});
export default connect(mapStateToProps, {})(Profile)
actions.js
export const fetchUser = (.....) => dispatch => {
fetch()
.....
}
reducers.js
case FETCH_USER:
return {
...state,
user: action.payload.user
};
As I understand it, the User component calls an action (fetchUser) from connect on componentWillMount(). That action calls an api, gets the data and the reducer adds that to the store within the state. The Profile component can then use connect to map the data from fetchUser in the store and display that data.
After reading some tutorials including https://github.com/reactjs/redux/blob/master/docs/basics/UsageWithReact.md
It looks like things can be simplified a bit without using classes.
If I were to change the User and Profile components to a more functional way, how would I do it?
eg.
const User = () => {
return (
<Profile />
)
}
how do I dispatch the fetchUser action and how do I simulate it to be called with the flow of componentWillMount()?
or am I just over complicating things?
There is also a way to support lifecycle methods in functional components.
https://www.npmjs.com/package/react-pure-lifecycle
import React from 'react';
import lifecycle from 'react-pure-lifecycle';
// create your lifecycle methods
const componentDidMount = (props) => {
console.log('I mounted! Here are my props: ', props);
};
// make them properties on a standard object
const methods = {
componentDidMount
};
const FunctionalComponent = ({children}) => {
return (
<div>
{children}
</div>
);
};
// decorate the component
export default lifecycle(methods)(FunctionalComponent);
I think you should keep using statefull components with redux...
https://medium.com/#antonkorzunov/2-things-about-purecomponent-you-probable-should-know-b04844a90d4
Redux connect — is a PureComponent.
Yes — a very important thing, a HoC for a molecule is a pure one. And works even inside other pure components. And gets store from a current context.
Same is working, for example, for styled-component — you can wrap it with PureComponent, but it will still react to Theme changes.
Solution is simple — bypass logic, use old school events bus, subcribe, wait and emit events.
Styled-componets:
componentWillMount() {
// subscribe to the event emitter. This
// is necessary due to pure components blocking
// context updates, this circumvents
// that by updating when an event is emitted.
const subscribe = this.context[CHANNEL];
this.unsubscribe = subscribe(nextTheme => { <----- MAGIC
React-redux:
trySubscribe() {
if (shouldSubscribe && !this.unsubscribe) {
this.unsubscribe =
this.store.subscribe(this.handleChange); <----- MAGIC
}
}
componentDidMount() {
this.trySubscribe();
}
Thus, even if parent Pure Component will block any update enables you to catch a change, store update, context variable change, or everything else.
So — something inside pure components is very soiled and absolutely impure. It is driven by side effects!
But this bypass straight logic flow, and works just differently from the rest of application.
So — just be careful. And don’t forget about magic.
Aaaand….
And this is a reason, why any redux store update will cause redraw in each connected component, and why you should use reselect just next to connect HoC —
to stop unnecessary change propagation.
But you should read this from another point of view:
redux-connect is a source of a change propagation.
redux connect is the end of a change propagation. It is still PureComponent.
And this leads to quite handy thing — you can control change propagation with redux-connect only. Just create a boundaries for a change. Lets talk about this in another article.
Conclusion
Pure components keep your application fast. Sometimes — more predictable, but often — less predictable, as long they change the way application works.
Stateless components are not pure, and may run slower than PureComponents by any kind.
But… if you very wish to create a fast application with good user experience — you have to use Pure Component.
No choice. But, now — you know hidden truth, and knew some magic…
React recommends that ajax request be made in componentDidMount(), rather than in componentWillMount(). For more info on this, read this post.
Since you want to make ajax requests in componentDidMount(), you need a class. There are two ways of writing component definitions: functional component and the class component. Functional components are more concise, but you don't get component lifecycle methods like componentDidMount(). Think of it as just a render function that takes props as inputs and outputs DOMs (in JSX). To override those lifecycle methods, you need to define them as a class.
If you want to use Redux, and want to make ajax requests in a Redux action, you should import the action creator function (fetchUser(..) in your case) that makes the ajax request, and dispatch(fetchUser(..)) in componentDidMount(). connect(..)ed components get dispatch(..) function passed to it by Redux store.
If you want to see how it's done in other redux apps, see the official example apps in the redux.js repo, paying attention to actions and containers: https://github.com/reactjs/redux/tree/master/examples
In Your case you can continue with statefull components no wrong in that
,If you need to go with functional way
There is a work arround
https://github.com/mobxjs/mobx/issues/162
Suggestion
Calling the api in componentDidMount will make sense than
componentWillMount , Because you can show the user something is
fetching.
I think,User component is designed nicely.It will act as a container for Profile to provide the Data.
Instead of making Profile component class oriented,it should be Stateless.
Lets User component pass the required data for Profile component.
You don't need to connect Profile component using redux-connect.Just render it as a Child component of User.
Profile
const Profile = (props) => {
const {user, likeProfile} = props;
//likeProfile()//call like this using dom event or programmatically.
return (
<h1>{user.profile.name}</h1>
)
}
You need to make some changes in User component.
Get the state for Profile component via mapStateToProps.
class User extends React.Component {
componentWillMount() {
this.props.fetchUser(.....);
}
render() {
const {user, likeProfile} = this.props;
return (
<Profile user= {user} likeProfile={likeProfile} /> //passed the user data to Profile component vua User
)
}
Map the user state for Profile in User connect.
const mapStateToProps = (state)=>{
return{
user : state.somereducerkey.user //this will be accessible in Profile via props { user}
}
}
export default connect(mapStateToProps, {fetchUser, likeProfile})(User);
On my React + Redux client app, I need to get the active user info (fetch from myapp.com/users/me) and keep it somewhere so that I can access it from multiple components.
I guess window.activeUser = data would not be the best practice. But I could not find any resource about the best practice of doing that. What would be the best way to do what I want?
you can keep it in a separate reducer, and then import multiple parts of your state with connect() in your components.
Say if you have 2 reducers called users.js and tags.js which are combined with combineReducers when setting up your store. You would simply pull different parts by passing a function to your connect() call. So using es6 + decorators:
const mapStateToProps = state => {
return {users: state.users, tags: state.tags}
}
#connect(mapStateToProps)
export default class MyComponent extends React.Component {
and then down in your render function:
return (
<div>
<p>{this.props.users.activeUsernameOrWhatever}</p>
<p>{this.props.tags.activeTags.join('|')}</p>
</div>
);
So your different reducer states become objects on this.props.
You can use React's context, HOC or global variables to make your data available to multiple components, via context
Something like...
class ParentDataComponent extends React.Component {
// make data accessible for children
getChildContext() {
return {
data: "your-fetchet-data"
};
}
render() {
return < Child />
}
}
class Child extends React.Component {
render() {
// access data from Parent's context
return (<div> {this.context.data} </div>);
}
}
create an action creator and call it on componentWillMount of the appropriate component so it runs right before your component mounts, and in the action creator fetch the data you need and pass it to a reducer. in that reducer you can keep the data you want throughout your application. so whenever you needed the data you can retrieve it from redux state. this tutorial from official redux website covers everything you need to know. mention me if you had any questions.