I am working on React app where the state is managed by redux. I am using actions.js file to fetch JSON data and store it directly in the store. The initial Store has just one key (data) in its obj with null as its value.
I use componentDidMount() Lifecycle to call the function which updates the store's data key with the JSON data I receive. However, whenever I load my app it gives an error because it finds the data value as null.
I get it. componentDidMount() executes after the app is loaded and the error doesn't let it execute. I tried using componentWillMount() but it also gives the same error. ( Which I use in JSX )
When I try to chanage the data's value from null to an empty obj it works for some level but after I use it's nested objects and arrays. I get error.
I wanna know what is the way around it. What should I set the vaue of inital State or should you use anyother lifecycle.
If your primary App component can't function properly unless the state has been loaded then I suggest moving the initialization logic up a level such that you only render your current component after the redux state has already been populated.
class version
class LoaderComponent extends React.Component {
componentDidMount() {
if ( ! this.props.isLoaded ) {
this.props.loadState();
}
}
render() {
if ( this.props.isLoaded ) {
return <YourCurrentComponent />;
} else {
return <Loading/>
}
}
}
export default connect(
state => ({
isLoaded: state.data === null,
}),
{loadState}
)(LoaderComponent);
Try something like this. The mapStateToProps subscribes to the store to see when the state is loaded and provides that info as an isLoaded prop. The loadState in mapDispatchToProps is whatever action creator your current componentDidMount is calling.
hooks version
export const LoaderComponent = () => {
const dispatch = useDispatch();
const isLoaded = useSelector(state => state.data === null);
useEffect(() => {
if (!isLoaded) {
dispatch(loadState());
}
}, [dispatch, isLoaded]);
if (isLoaded) {
return <YourCurrentComponent />;
} else {
return <Loading />
}
}
And of course you would remove the fetching actions from the componentDidMount of the current component.
Related
I am trying to understand someone else their code but have difficulty understand the interaction between Redux and React.
On a React page, I invoke a Redux action called getSubscriptionPlan. Inside that Redux action, I see it is able to load the correct data (point 1 below). This uses a reducer, in which I can again confirm the correct data is there (point 2 below).
Then the logic returns to the React page (point 3 below). I now would expect to be able to find somewhere in the Redux store the previously mentioned data. However, I can't find that data listed anywhere... not in this.state (where I would expect it), nor in this.props. Did the reducer perhaps not update the store state...?
What am I doing wrong and how can I get the data to point 3 below?
React page:
import { connect } from "react-redux";
import { getSubscriptionPlan } from "../../../appRedux/actions/planAction";
async componentDidMount() {
let { planId } = this.state;
await this.props.getSubscriptionPlan(planId);
// 3. I can't find the data anywhere here: not inside this.state and not inside this.props.
this.setState({plan: this.state.plan});
}
componentDidUpdate(prevProps, prevState) {
if (prevProps.payment.paymentData !== this.props.payment.paymentData) {
this.setState({
checkout: this.props.payment.paymentData,
plan: this.props.payment.paymentData.plan,
});
}
}
const mapStateToProps = (state) => {
return {
plan: state.plan,
};
};
const mapDispatchToProps = (dispatch) => {
return bindActionCreators(
{ getSubscriptionPlan }, dispatch
);
};
export default withRouter(
connect(mapStateToProps, mapDispatchToProps)(Checkout)
);
Redux action:
export const getSubscriptionPlan = (id) => {
let token = getAuthToken();
return (dispatch) => {
axios
.get(`${url}/getSubscriptionPlan/${id}`, {
headers: { Authorization: `${token}` },
})
.then((res) => {
if (res.status === 200) {
// 1. From console.log(res.data) I know res.data correctly now contains the data
return dispatch({
type: GET_PLAN_SUCCESS,
payload: res.data,
});
})
};
};
Reducer:
export default function planReducer(state = initial_state, action) {
switch (action.type) {
case GET_PLAN_SUCCESS:
// 2. I know action.payload, at this point contains the correct data.
return { ...state, plan: action.payload };
default:
return state;
}
}
You are getting tripped up on how Redux works.
Redux does not use react component state. It manages state separately, and passes that state to components as props. When you call getSubscriptionPlan, you asynchronously dispatch an event to Redux, which handles the event and updates store state in the reducer. This state is the passed to the connected components mapStateToProps function, mapped to props, and then passed as props to your component. Passing new props triggers a componentDidUpdate and a rerender of the component.
A few key things here.
Redux does not interact with component state unless you explicitly set state with props passed from Redux.
Redux is asynchronous. That means that when you make a change to state via dispatch, the change is not immediately available in the component, but only available when new props are passed. It's event driven, not data binding. As a result, in your code you woun't see the plan prop in componentDidMount because at the time componentDidMount the call to getSubscriptionPlan hasn't happened.
You should see the prop populated in this.props in componentDidUpdate and in render before the didUpdate.
When working with react, it's best to think of components as basically functions of props with some extra lifecycle methods attached.
I'm using react + redux + redux saga
I'm facing the issue that when I'm rendering the page (GET call)
The calls should be like:
constructor
render()
componentDidMount
render()
But I'm just reaching up to componentDidMount, mapDispatchToProps is dispatching the action, API call is working by which getting the response from the server and the data is updated into the state.
BUT somewhere it gets lost and my component is not even re rendering.
Up to the reducer, I'm getting the data where I'm returning action.items.
itemReducer.js
const itemReducer = (state = initialState, action) => {
switch (action.type) {
case types.GET_ALL_ITEMS_SUCCESS:
console.log("itemReducer-----", action.items); //getting the data over here
return action.items;
default:
return state;
}
};
itemPage.js (component)
class ItemsPage extends React.Component {
componentDidMount() {
this.props.loadItems();
}
render() {
const { items } = this.props; // not even it renders, so not getting data
...
return (<div>...</div>);
}
}
const mapStateToProps = (state) => {
return {
items: state.items,
};
};
const mapDispatchToProps = (dispatch) => {
return {
loadItems: () => dispatch(loadAllItemsAction()),
};
};
export default connect(mapStateToProps, mapDispatchToProps)(ItemsPage);
Please give some suggestions, Thanks in advance :D
There isn't issue in the code that you posted. To make sure I pretty much copy pasted the code you shared, filled in the missing parts and it works just fine:
https://codesandbox.io/s/3tuxv?file=/src/index.js
My guess what might be wrong is that your items are not stored in state.items but under some different path or you might be missing the react-redux Provider, but it is impossible to say for sure without seeing more of your code.
You need to understand that the calls of render/componentDidMount are not so linear as it could be expected. componentDidMount fires when all children were mount. And it doesn't means that render() was finished already.
Read here for more info:
https://github.com/facebook/react/issues/2659
In my react app I have component named profile, and I am fetching data from server and showing it inside that component. I am using redux and redux-thunk along with axios. With help of mapDispatchToProps function, i am calling redux action for fetching that data when component is mounted and saving it to redux state. After that, using mapStateToProps function i am showing that data on the screen via props. That works fine. Now I want to have possibility to edit, for example, first name of that user. To accomplish that i need to save that data to component state when data is fetched from server, and then when text field is changed, component state also needs to be changed. Don't know how to save data to component sate, immediately after it is fetched.
Simplified code:
const mapStateToProps = (state) => {
return {
user: state.user
}
}
const mapDispatchToProps = (dispatch) => {
return {
getUserData: () => dispatch(userActions.getUserData())
}
}
class Profile extends Component {
state:{
user: {}
}
componentDidMount (){
this.props.getUserData()
// when data is saved to redux state i need to save it to component state
}
editTextField = () => {
this.setState({
[e.target.id]: e.target.value
})
};
render(){
const { user } = this.props;
return(
<TextField id="firstName"
value={user.firstName}
onChange={this.editTextField}
/>
)
}
}
You can use componentDidUpdate for that or give a callback function to your action.
I will show both.
First lets see componentDidUpdate,
Here you can compare your previous data and your present data, and if there is some change, you can set your state, for example if you data is an array.
state = {
data: []
}
then inside your componentDidUpdate
componentDidUpdate(prevProps, prevState) {
if(prevProps.data.length !== this.props.data.length) {
// update your state, in your case you just need userData, so you
// can compare something like name or something else, but still
// for better equality check, you can use lodash, it will also check for objects,
this.setState({ data: this.props.data});
}
}
_.isEqual(a, b); // returns false if different
This was one solution, another solution is to pass a call back funtion to your action,
lets say you call this.props.getData()
you can do something like this
this.props.getData((data) => {
this.setState({ data });
})
here you pass your data from redux action to your state.
your redux action would be something like this.
export const getData = (done) => async dispatch => {
const data = await getSomeData(); // or api call
// when you dispatch your action, also call your done
done(data);
}
If you are using React 16.0+, you can use the static method getDerivedStateFromProps. You can read about it react docs.
Using your example:
class Profile extends Component {
// other methods here ...
static getDerivedStateFromProps(props) {
return {
user: props.user
}
}
// other methods here...
}
I currently initialize the relevant store data (galleries and pieces) on the "Layout" componentDidMount. This data is fetched from an API.
const mapDispatchToProps = {
GetRooms,
GetPieces
}
class Layout extends React.Component {
...
componentDidMount () {
this.props.GetRooms()
this.props.GetPieces()
}
...
render () {
return (
...
<Route path="/Gallery/:roomName" component={Gallery} />
...
)
}
}
I have a separate "Gallery" component that is loaded through a react-router Route inside the Layout component. Gallery's mapStateToProps uses a selector function to filter the requested gallery object and appends a property containing an array of related piece objects.
const GetRoomByName = (state, roomName) => {
const room = state.rooms.all.find(room =>
room.Name === roomName
)
if (!room) return
room.Pieces = state.pieces.all.filter(piece =>
piece.RoomId === room.Id
)
return room
}
const mapStateToProps = (state, { match }) => ({
room: GetRoomByName(state, decodeURIComponent(match.params.roomName))
})
class Gallery extends React.Component {
...
render () {
const { room } = this.props
if (room === undefined) return <h3>Loading...</h3>
return (
...
{room.Pieces.map(piece =>
...
)}
...
)
}
}
When I navigate to this page from the home page, the store is already initialized and the selector executes properly.
But if the route that loads the "Gallery" component is refreshed or directly loaded from the address bar, the data isn't present in the store yet, and when it does load the component does not update. I can run a console log and the room object gets rendered, but the Pieces property doesn't trigger a rerender when it is loaded into the store.
Thank you for your assistance
The problem has to do with how the connect function determines if the component should rerender. connect only rerenders the component if one of the properties in mapStateToProps changes, determined using a shallow comparison. Because it uses a shallow comparison, the component will not rerender unless the reference returned by GetRoomByName changes. To fix this, you should return a new object from GetRoomByName rather than modifying the object that exists in the state (which can lead to other had to diagnose issues down the road as well).
const GetRoomByName = (state, roomName) => {
const room = state.rooms.all.find(room =>
room.Name === roomName
);
if (!room) return
const pieces = state.pieces.all.filter(piece =>
piece.RoomId === room.Id
);
return {
...room,
Pieces: pieces
};
}
This isn't so efficient though since it will return a new object every time, causing the component to rerender more frequently than necessary. Depending on your scenario this may not be an issue. If it is, you should look into reselect, which will cache the result of GetRoomByName.
Also, the reason your code works when navigating from the home page is that you are returning a different reference from GetRoomByName because the roomName changes.
I'm using Redux and React to load data from a web service which is working well. I'd like to make small non-webservice-based changes in the UI in response to an action. A simplified example:
class SmartComponent extends React.Component {
handleClick = (e) => {
// how to best handle a simple state change here?
}
render() {
const { displayMessage } = this.props
return (
<DumbComponent message={displayMessage}/>
<button onclick={this.handleClick}>Change Message</button>)
}
}
const mapStateToProps = state => {
// state variables linked in the reducer
}
export default connect(mapStateToProps)(SmartComponent)
let DumbComponent = ({ message }) => {
return ({message})
}
If I modify the state in SmartComponent, for instance, by using this.setState, the props of SmartComponent will not be automatically updated. I believe it's a React anti-pattern to directly modify the props of SmartComponent. Is the best way to update the message in DumbComponent to make an action creator and link it in the reducer? That seems a bit overkill for a simple message change.
Yes, you should link it to the reducer.
However this is not mandatory:
How to do it
One other way to do this would be to store the message in the state of the SmartComponent.
Beware about the fact that Redux is no longer the single source of truth for the message.
class SmartComponent extends React.Component {
constructor(props) {
super(props)
// Initialize state based on props
this.state = {
message: props.message,
}
}
componentWillReceiveProps(nextProps) {
// Handle state update on props (ie. store) update
this.setState({ message: ... })
}
handleClick = (e) => {
this.setState({ message: ... })
}
render() {
const { displayMessage } = this.state
return (
<DumbComponent message={displayMessage}/>
<button onclick={this.handleClick}>Change Message</button>)
}
}
const mapStateToProps = state => {
// state variables linked in the reducer
}
export default connect(mapStateToProps)(SmartComponent)
let DumbComponent = ({ message }) => {
return ({message})
}
Should you do it ?
If the data you display in this component can be completely isolated from the rest of your application, that is to say no dispatched action could modify it, and no other component need it, keeping this data in the store can be unnecessary.
I mostly use this method to perform optimistic updates to the view component without altering the store until new value is saved by the server.