I am trying to set the state to the current select item in the dropdown. I thought there would be an easier way of doing this than going through the whole, action/reducer chain. But in this case setState will always be empty and componentWillReceiveProps will never be called.
Is there a way to accomplish this?
componentWillReceiveProps(nextProps) {
console.log("collection next props", nextProps);
this.setState({
currentList: nextProps.currentList,
});
}
handleChange (e) {
console.log('handle change called', e.target.value); //Value is received
//this.setState({value: e.target.value});
this.setState({currentList: e.target.value}); //This is never getting the value
this.props.fetchlistOfAssets(e.target.value); //This action executes without problem
};
render() {
/* Read from market and last price */
const postItems = this.props.indexes.map(post => (
<option key={post} value={post}>{post}</option>
));
return (
<div>
<h1>Select index</h1>
<select name="index" onChange={this.handleChange}>{postItems}</select>
</div>
);
}
}
Edit adding connect and mapState
const mapStateToProps = state => ({
indexes: state.posts.indexdays,
currentList: state.posts.currentList
});
export default connect(
mapStateToProps,
{ fetchIndexDays, fetchlistOfAssets }
)(CollectionDropDown);
Related
After the first render, the useReducer hook doesn't react to changes in its initialArg (second positional) argument. It makes it hard to properly sync it with an external value, without having to rely on an extra cycle by dispatching a reset action inside a useEffect hook.
I built a minimal example. It's a simple, formik-like, form provider. Here's what it looks like:
// App.js
const users = {
1: {
firstName: 'Paul',
lastName: 'Atreides',
},
2: {
firstName: 'Duncan',
lastName: 'Idaho',
},
};
const App = () => {
const [id, setId] = useState(1);
return (
<>
<div>Pick User</div>
<button onClick={() => { setId(1); }} type="button">User 1</button>
<button onClick={() => { setId(2); }} type="button">User 2</button>
<FormProvider initialValues={users[id]}>
<Editor />
</FormProvider>
</>
);
};
// FormProvider.js
const reducer = (state, action) => {
switch (action.type) {
case 'UPDATE_FIELD':
return { ...state, [action.field]: action.value };
default:
throw new Error();
}
};
const FormProvider = ({ children, initialValues }) => {
const [values, dispatch] = useReducer(reducer, initialValues);
const handleChange = useCallback((evt) => {
dispatch({
field: evt.target.name,
type: 'UPDATE_FIELD',
value: evt.target.value,
});
}, []);
return (
<FormContext.Provider value={{ handleChange, values }}>
{children}
</FormContext.Provider>
);
};
// Editor.js
const Editor = () => {
const { handleChange, values } = useContext(FormContext);
return (
<>
<div>First name:</div>
<input
name="firstName"
onChange={handleChange}
value={values.firstName}
/>
<div>First name:</div>
<input
name="lastName"
onChange={handleChange}
value={values.lastName}
/>
</>
);
};
If you open the demo and click on the User 2 button, you'll notice that nothing happens. It's not surprising since we know that the useReducer hook gets initialised once using the provided initialArg argument and never reads its value again.
What I expect is the useReducer state to reflect the new initialArg prop, i.e. I want to see "Duncan" in the First name input after clicking on the User 2 button.
From my point of vue, I can see two options:
1. Passing a key prop to the FormProvider component.
// App.js
const App = () => {
// ...
return (
<>
{/* ... */}
<FormProvider key={id} initialValues={users[id]}>
<Editor />
</FormProvider>
</>
);
};
This will indeed fix the problem by destroying and re-creating the FormProvider component (and its children) every time the id changes. But it feels like a hack to me. Plus, it seems inefficient to rebuild that entire part of the tree (which is substantial in the real application) just to get that input values updated. However, this seems to be a common fix for such problems.
2. Dispatch a RESET action whenever initialValues changes
// FormProvider.js
const reducer = (state, action) => {
switch (action.type) {
case 'UPDATE_FIELD':
return { ...state, [action.field]: action.value };
case 'RESET':
return action.values;
default:
throw new Error();
}
};
const FormProvider = ({ children, initialValues }) => {
// ...
const isFirstRenderRef = useRef(true);
useEffect(() => {
if (!isFirstRenderRef.current) {
dispatch({
type: 'RESET',
values: initialValues,
});
}
}, [initialValues]);
useEffect(() => {
isFirstRenderRef.current = false;
}, []);
// ...
};
This will work as well, but, because it's happening inside a useEffect hook, it will require an extra cycle. It means that there'll be a moment where the form will contain stale values. If the user types at that moment, it could cause a race condition.
3. Idea
I read in this article by Mark Erikson that:
Function components may call setSomeState() directly while rendering, as long as it's done conditionally and isn't going to execute every time this component renders. [...] If a function component queues a state update while rendering, React will immediately apply the state update and synchronously re-render that one component before moving onwards.
So it seems that I should be able to call dispatch({ type: RESET, values: initialValues }); directly from the body of the function, under the condition that initialValues did change (I'd use a ref to keep track of its previous value). This should result in the state being updated in just one cycle. However, I couldn't get this to work.
——
What do you think is best between option 1, 2 and (3). Any advice/guidance on how I should address this problem?
I have an array of objects in a useState hook with which i rendered input elements.
The state doesn't get updated when the input element changes.
Here Is My Code.
ProceduralResponseAnswerCreate Component
const ProceduralResponseAnswerCreate = () => {
const [proceduralAnswers, setProceduralAnswers] = useState([{ "value": "One" }, { "value": "two" }])
return <>
<ol>
{proceduralAnswers.map((answer, answer_index) => <input key={answer_index} style={inputStyle} onChange={(event) => updateAnswerValue({ event, setProceduralAnswers, answer_index })} value={answer.value} />)}
</ol>
</>
}
export default ProceduralResponseAnswerCreate
updateAnswerValue function
export const updateAnswerValue = ({ event, setProceduralAnswers, answer_index }) => {
setProceduralAnswers(state => {
var newState = state;
var currentAnswer = newState.filter((state_1, index) => index === answer_index)[0]
currentAnswer.value = event.target.value
return newState
})
}
I think it doesn't work because the next state has the same Reference as the previous state, you only change the value of one element. The useState hook will trigger a rerender, if the reference changes. So your Callback must look like this.
setProceduralAnswers(state => {
let newState = state;
let currentAnswer = newState.filter((state_1, index) => index === answer_index)[0]
currentAnswer.value = event.target.value
return [...newState]
})
try this
export const updateAnswerValue = ({ event, setProceduralAnswers, answer_index }) => {
setProceduralAnswers(state => {
var newState = state;
newState[answer_index].value = event.target.value
return newState
})
}
You are returning the newState instead of the currentAnswer.
First off, if you're only trying to find one item use [].find not filter.
var newState = state; does not give you a fresh copy, change newState, and you'll be changing state too, you need to do var newState = [...state]; (warning: this is a shallow copy only).
It looks like you think currentAnswer shares a reference with newState in some way, which it doesn't. Whenever you run map, find, filter or reduce you're getting a fresh copy of the array so there will not be a link between the 2.
A good bet here is to just map the state
export const updateAnswerValue = ({
event,
setProceduralAnswers,
answer_index
}) => {
setProceduralAnswers((state) => state.map((state_1, index) => {
if (index === answer_index) {
return {
...state_1,
value: event.target.value
}
}
return state_1;
}));
};
What I want to do
When state changes, I would like to fetch data from API and set it to state.
Problem
When I load a page, componentDidUpdate is automatically emitted although anything doesn't change and this is initial render.
I am beginner to React.
I would like to get data from API when I input some data and state changes.
However, when I load a page I got an error that cannot property map of undefined.
Apparently, componentDidUpdate is called for some reasons when the page is first rendered.
In fact, I compared prevState.line to this.state.line, and then I found prevState.line undefined.
I mean, componentDidUpdate is emitted before "" that is an initial value of this.state.line is set to this.state.line.
I just would like to prevent componentDidUpdate from being initially called.
If you know a way to do that, I would like you to tell me that and why it is happening.
Thank you very much.
=========== ============ ============
My code is like this.
class User_Add_PickUp_Form extends Component {
constructor(props) {
super(props);
this.state = {
owner: this.props.loginUser,
lines: '',
stations: '',
textInput: '',
allLines: '',
allStations: '',
};
this.handleChange = this.handleChange.bind(this);
}
spreadAndSetState = (key, value) => {
this.setState({ ...this.state, [key]:value });
};
componentDidMount() {
console.log('Original is ' + this.state.lines)
axios
.get('http://express.heartrails.com/api/json?method=getLines&prefecture=TOKYO')
.then((res) => {
console.log(res.data)
this.setState({ allLines: res.data.response.line })
})
.catch((err) => console.log(err));
}
componentDidUpdate(prevState){
console.log(prevState)
console.log(this.state)
if(prevState.lines != this.state.lines){
axios.get('http://express.heartrails.com/api/json?method=getStations&line=' + this.state.lines)
.then((res)=> {
//
// res.data.response.stations is going to be an array
//
res.data.response.station.map((station) => {
this.spreadAndSetState(this.state.allStations, station.name)
})
})
}
}
handleChange = (e) => {
const name = e.target.name;
const value = e.target.value;
this.spreadAndSetState(name,value)
};
render() {
const { owner, lines, stations, textInput, allLines, allStations } = this.state;
if (allLines === '') {
return <CircularProgress />;
} else {
return (
<div>
<h2>Add Pickup Places</h2>
<select name="lines" onChange={this.handleChange}>
<option value="">Choose a line</option>
{allLines.map((line) => {
return <option value={line}>{line}</option>;
})}
</select>
<select name="lines" onChange={this.handleChange}>
<option value="">Choose a station</option>
{allLines.map((line) => {
return <option value={line}>{line}</option>;
})}
</select>
</div>
);
}
}
}
// EditableNote.js
function EditableNote({ note }) {
const [editableNote, setEditableNote] = useState(note);
const { title, content } = editableNote;
const dispatch = useDispatch();
useEffect(() => {
setEditableNote(note);
}, [note]);
›
useEffect(() => {
dispatch(saveEditableNote(editableNote)); // I think here is problem
}, [dispatch, editableNote]);
const handleBlur = e => {
const name = e.target.id;
const value = e.currentTarget.textContent;
setEditableNote({ ...editableNote, [name]: value });
};
return (
<EditNote spellCheck="true">
<NoteTitle
id="title"
placeholder="Title"
onBlur={handleBlur}
contentEditable
suppressContentEditableWarning={true}>
{title}
</NoteTitle>
<NoteContent
id="content"
placeholder="Note"
onBlur={handleBlur}
contentEditable
suppressContentEditableWarning={true}>
{content}
</NoteContent>
</EditNote>
);
}
export default EditableNote;
I have EditableNote component which is contentEditable. I set its initial state through props from its parent(Note). So if something is changed in note, then editableNote has to changed.
To keep recent props state, I use useEffect. Everything seems working well.
Here is an issue. If I first change color of note and typing, it is updated as expected. But on contrast, if I first typing and change color, editableNote state is not updated.
// Reducer.js
case actions.GET_NOTE_COLOR:
return {
...state,
bgColor: action.payload
}
case actions.CHANGE_NOTE_COLOR:
return {
...state,
notes: state.notes.map(note => note.id === action.payload ?
{ ...note, bgColor: state.bgColor }
: note
)
};
case actions.SAVE_EDITABLE_NOTE: // payload is old value
return {
...state,
editableNote: action.payload,
}
I check what happened in an action. I found everything works until CHANGE_NOTE_COLOR but when dispatch SAVE_EDITABLE_NOTE, its payload is not updated!
I have no idea.. plz.. help me...TT
You have to use the connect wrapper provided by redux to connect actions and state of redux to your components
https://react-redux.js.org/api/connect
I'm trying to debounce a component in my webapp. Actually it is a filter for the maxPrice and if the user starts to print, the filter starts to work and all the results disappear until there is a reasonable number behind it.
What I tried so far:
import _ from 'lodash'
class MaxPrice extends Component {
onSet = ({ target: { value }}) => {
if (isNaN(Number(value))) return;
this.setState({ value }, () => {
this.props.updateMaxPrice(value.trim());
});
};
render() {
const updateMaxPrice = _.debounce(e => {
this.onSet(e);
}, 1000);
return (
<div>
<ControlLabel>Preis bis</ControlLabel><br />
<FormControl type="text" className={utilStyles.fullWidth} placeholder="egal"
onChange={updateMaxPrice} value={this.props.maxPrice}
/>
</div>
);
}
}
I'm getting the error
MaxPrice.js:11 Uncaught TypeError: Cannot read property 'value' of null
at MaxPrice._this.onSet (MaxPrice.js:11)
at MaxPrice.js:21
at invokeFunc (lodash.js:10350)
at trailingEdge (lodash.js:10397)
at timerExpired (lodash.js:10385)
In my old version I had onChange={this.onSet} and it worked.
Any idea what might be wrong?
As you mentioned in comments, it's required to use event.persist() to use event object in async way:
https://facebook.github.io/react/docs/events.html
If you want to access the event properties in an asynchronous way, you
should call event.persist() on the event, which will remove the
synthetic event from the pool and allow references to the event to be
retained by user code.
It means such code, for example:
onChange={e => {
e.persist();
updateMaxPrice(e);
}}
Here is my final solution. Thanks to lunochkin!
I had to introduce a second redux variable so that the user see's the values he is entering. The second variable is debounced so that the WepApp waits a bit to update.
class MaxPrice extends Component {
updateMaxPriceRedux = _.debounce((value) => { // this can also dispatch a redux action
this.props.updateMaxPrice(value);
}, 500);
onSet = ({ target: { value }}) => {
console.log(value);
if (isNaN(Number(value))) return;
this.props.updateInternalMaxPrice(value.trim());
this.updateMaxPriceRedux(value.trim());
};
render() {
return (
<div>
<ControlLabel>Preis bis</ControlLabel><br />
<FormControl type="text" className={utilStyles.fullWidth} placeholder="egal"
onChange={e => {
e.persist();
this.onSet(e);
}} value={this.props.internalMaxPrice}
/>
</div>
);
}
}
function mapStateToProps(state) {
return {
maxPrice: state.maxPrice,
internalMaxPrice: state.internalMaxPrice
};
}
function mapDispatchToProps(dispatch) {
return bindActionCreators({updateMaxPrice:updateMaxPrice,
updateInternalMaxPrice:updateInternalMaxPrice}, dispatch);
}
export default connect(mapStateToProps, mapDispatchToProps)(MaxPrice);