class RaisablePaper extends Component {
constructor(props) {
super();
this.state = {
state1: "state1",
openNow: props.boxOpen,
};
}
}
I am trying to send value to this class by doing <RaisablePaper boxOpen={this.state.dOpen}/>. But whenever the dOpen gets changed it does not seem to update the openNow. Help would very much appreciated.
You are setting the state before mounting the component in the constructor, which will not be fired again when the props change. For that you can use React's componentWillReceiveProps, which will be called when new props are sent to the component.
class RaisablePaper extends Component {
constructor(props) {
super();
this.state = {
state1: "state1",
openNow: props.boxOpen
};
}
componentWillReceiveProps(props) {
this.setState({
openNow: props.boxOpen
});
}
}
It would be simpler to use the props directly instead of worrying about syncing it to your state. It's a good idea in general to rely on props as much as possible, and only involve state when absolutely necessary.
But Fabian Schultz is absolutely right -- your constructor only runs once, before the component is mounted, so you'll never receive the subsequent updates if the component is relying on state which is initialized during construction.
I'm just imagining how you're using the boxOpen state to show an example; you can follow the same general idea with whatever your render method is doing.
class RaisablePaper extends Component {
render() {
return (
<div className={this.props.boxOpen ? 'is-open' : ''}>
Here's some content...
</div>
);
}
}
Related
I'm extremely new to react and javascript so I'm sorry if I'm asking this wrong.
This is for a group project which means I most likely don't understand the project 100%
The older sibling has this nice prop that I want to use:
```
export default class OlderSibling extends Component {
state = {
currentCity: city //(that was gathered from a bunch of other steps)
};
render() {
return(
)
}
}
```
The parent file doesn't have this prop, but it does have its own stuff. I do not care for these other props though.
```
class Parent extends Component {
constructor(props) {
super(props)
this.state = {
flower: 'red'
}
}
render() {
return (
<OlderSibling/>
<YoungerSibling/>
)
}
}
```
The younger sibling (the one that wants current city) has a bunch of this.state properties that I do not want to share with others but just want the older sibling's stuff (I guess like what younger siblings normally do).
```
export class YoungerSibling extends Component {
constructor(props) {
super(props);
this.state = {
title: '',
description: []
}
}
render() {
return(
)
}
}
```
Just in case I wasn't clear, younger sibling just wants older sibling's this.state: currentCity that older Sibling worked so hard to gather.
I know I didn't put the code completely, but if you want to critique it anyway, please do! I am still learning and I welcome every bit of feedback!
I looked up ways to do this, but they're all about transferring parent to child which is not what I want. I also read that there was Redux that could handle this?? I don't know if my fellow groupmates are interested in that just yet.
Thank you for your time in reading this!
EDIT:
[ SOLVED ]
I just want to edit and say thank you to #soupette, #Liam, #[Denys Kotsur], and #Tomasz for helping me to understand react a bit more. I realize that this post was very much a spoon feeding request and you all helped away. Thank you!
Also, just in case anybody else ran into this issue, don't forget to call it on Younger Sibling as this.props.currentCity .
As the previous answer suggests lift the state up I also prefer to use it
Here's an example
You can do something like:
class Parent extends Component {
state = {
flower: 'red'
currentCity: '',
};
updateCurrentCity = (currentCity) => this.setState({ currentCity });
render() {
return (
<OlderSibling updateCurrentCity={this.updateCurrentCity} />
<YoungerSibling city={this.state.currentCity} />
);
}
}
then in your OlderSibling you can update the parent's state with a function:
export default class OlderSibling extends Component {
state = {
currentCity: city //(that was gathered from a bunch of other steps)
};
componentDidUpdate(prevProps, prevState) {
if (prevState.currentCity !== this.state.currentCity) {
this.props.updateCurrentCity(this.state.currentCity);
}
}
render() {
return(
);
}
}
You should create Parent component for these two ones and keep state there.
Also, you should pass it into two children (YoungerSibling and OlderSibling) as a prop and add inverse data flow for OlderSibling so when city is changed in the OlderSibling then ParentSibling should know about this.
For example:
Parent.jsx
class Parent extends React.Component {
constructor(props) {
super(props);
this.state = {
currentCity: ''
}
}
currentCityChangeHandler = city => {
this.setState({currentCity: city});
};
render() {
const { currentCity } = this.state;
return(
...
<OlderSibling
currentCity={currentCity}
onCurrentCityChange={this.currentCityChangeHandler}
/>
<YoungerSibling currentCity={currentCity} />
...
)
}
}
OlderSibling.jsx
class OlderSibling extends React.Component {
...
// Somewhere when new city is coming from
// You should pass it into the callback
newCityComingFunction() {
const city = 'New York';
// Pass the new value of city into common `Parent` component
this.props.onCurrentCityChange(city);
}
...
}
So in this case it will allow you to use this param in both cases and it will be keep updated.
In addition, you should use this.props.currentCity in the OlderSibling instead of using this.state.currentCity in this component because it's value is moved into Parent's component state.
Hope it will helps.
You got two choices.
use external state management library like redux.
lift the state up - which means Parent component will hold currentCity in the state.
There could be 3rd option of using contex API but I'm not sure how to do it here.
who knows how change props in my component use refs in react js ?
<MyComponent
ref={'input1'}
name={'input1'}
label={interestsName}
disabled={ false}
onChange={this.myFunction}/>
after onChange i call function with
myFunction =()=>{console.log(this.rews[input1].props.disable);}
May I change props use refs without use state? Because I have many '15' components such as this component. Thanks.
You cannot change props from child class, for more please refer to link.
For your functionality use you can use state to change value on the change event. And one more thing you should keep the logic of changing component properties should remain inside a component. This will help us to maintain different states for different components.
class MyComponent extends React.Component {
constructor(props) {
this.state = {
disable: props.disabled
};
}
myFunction() {
console.log(this.state);
}
}
You can iterate over the above component and it can be used for 15 times and different states can be managed for every element
You shouldn't use ref in this case, you should use states to change your child props:
class MainComponent extends React.Component {
constructor(props) {
super(props)
this.state = {
disable: false,
};
this.onChange = this.onChange.bind(this);
}
onChange() {
this.setState({ disable: true });
}
<MyComponent
name="input1"
label={interestsName}
disabled={this.state.disable}
onChange={this.onChange}
/>
}
In <MyComponent> use componentWillReceiveProps() to detect new props value.
I'm fairly new to react and struggle to update a custom component using componentDidMount and setState, which seems to be the recommended way of doing it. Below an example (includes an axios API call to get the data):
import React from 'react';
import {MyComponent} from 'my_component';
import axios from 'axios';
export default class Example extends React.Component {
constructor(props) {
super(props);
this.state = {
data: []
};
}
GetData() {
return axios.get('http://localhost:5000/<route>');
}
componentDidMount() {
this.GetData().then(
(resp) => {
this.setState(
{data: resp.data}
)
}
)
}
render() {
return (
<MyComponent data={this.state.data} />
);
}
}
Doing console.log(this.state.data) just below render() shows that this.state.data does indeed get updated (from [] to whatever the API returns). However, the problem appears to be that MyComponent isn't rendered afresh by componentDidMount. From the Facebook react docs:
Setting state in this method will trigger a re-rendering.
This does not seem to be the case here: The constructor of MyComponent only gets called once (where this.props.data = []) and the component does not get rendered again. I'd be great if someone could explain why this is and whether there's a solution or a different way altogether to get the updating done.
UPDATE
I've added the code for MyComponent (minus some irrelevant features, as indicated by ...). console.log(data_array) prints an empty array.
import React from 'react';
class DataWrapper {
constructor(data) {
this._data = data;
}
getSize() {
return this._data.length;
}
...
}
export class MyComponent extends React.Component {
constructor(props) {
super(props);
this._dataWrapper = new DataWrapper(this.props.data);
this.state = {
data_array: this._dataWrapper,
};
}
render() {
var {data_array} = this.state;
console.log(data_array);
return (
...
);
}
}
You are falling victim to this antipattern.
In MyComponent constructor, which only gets called the first time it mounts, passed your empty array through new DataWrapper and now you have some local state which will never be updated no matter what your parent does.
It's always better to have one source of truth, just one state object anywhere (especially for things like ajax responses), and pass those around via props. In fact this way, you can even write MyComponent as a simple function, instead of a class.
class Example extends Component {
state = { data: [] }
GetData() { .. }
componentDidMount() {
this.GetData().then(res =>
this.setState({data: new DataWrapper(res.data)})
)
}
render() { return <MyComponent data={this.state.data} /> }
}
...
function MyComponent (props) {
// props.data will update when your parent calls setState
// you can also call DataWrapper here if you need MyComponent specific wrapper
return (
<div>..</div>
)
}
In other words what azium is saying, is that you need to turn your receiving component into a controlled one. Meaning, it shouldn't have state at all. Use the props directly.
Yes, even turn it into a functional component. This helps you maintain in your mind that functional components generally don't have state (it's possible to put state in them but ... seperation of concerns).
If you need to edit state from that controlled component, provide the functions through props and define the functions in the "master" component. So the master component simply lends control to the children. They want anything they talk to the parent.
I'm not posting code here since the ammendment you need to make is negligible. Where you have this.state in the controlled component, change to this.props.
This may seem as a bit of a redundant question but I'm trying to access the final state of a child in React, after it has updated. I've been looking into the React LifeCycle docs (I think that might be the issue, but not sure), searched high and low, and can't quite figure it out.
I've got a component which needs to access the (final) value of the state of a child, once that child has done some updating (AJAX request which then does a few this.setStates).
So far, I'm able to access the entire state of that child, accessing through a ref (Inside componentDidMount), but when I try to access a specific value of said state, it returns null or undefined.
Here's some example code to explain (I'll try to spare you as much useless code as possible):
class Layout extends Component {
constructor(props) {
super(props);
}
componentDidMount(){
// This gives me the updated State where pageTitle = "Whatever"
console.log(this.refs.child1);
// However this gives me the initial State where pageTitle = null
console.log(this.refs.child1.state.pageTitle);
}
render(){
return (<div>
{React.cloneElement(
this.props.children,
{ref: 'child1'}
)}
</div>);
}
}
And here's the child component for reference (note: i'm using axios for my ajax requests):
export class ChildComponent extends Component {
constructor(props) {
super(props);
this.state = {
resultData: result,
pageTitle: null
}
}
componentDidMount(){
this.serverRequest = axios.get(apiUrl)
.then(function(result){
this.setState({
resultData: result,
pageTitle: result.pageTitle
});
}.bind(this))
}
render(){
return(<div>
{use of different this.state.resultData values works fine here}
</div>)
}
}
Appreciate any help that comes this way
To use a callback, add this code to the parent element:
handleAsyncDone(data) {
// Do whatever it is people do with data
}
And then pass that function to the child component, and in the childcomponent, add
this.props.handleAsyncDone(this.state);
Which will pass the child state back up to the parent.
I'm trying to use a stateful React component with ES6 but when I define a constructor the constructor will only be called once while the component is rendered multiple times (from its parent). Example shown below.
class SubComponent extends React.Component {
constructor(props) {
super(props);
console.log("Creating sub component");
this.state = { count: props.count };
}
render() {
console.log("Rendering sub component", this.state.count);
return (<div>count: {this.state.count}</div>);
}
}
class App extends React.Component {
constructor(props) {
super(props);
console.log("Creating app");
this.state = { count: 0 };
this.tick = this.tick.bind(this);
setInterval(this.tick, 1000);
}
tick() {
this.setState({ count: this.state.count + 1 });
}
render() {
console.log("Rendering app", this.state.count);
return (<SubComponent count={this.state.count} />);
}
}
This will not update the rendered output (it will always be count: 0) but the logs will output:
Creating app
Rendering app 0
Creating sub component
Rendering sub component 0
Rendering app 1
Rendering sub component 0
Rendering app 2
Rendering sub component 0
Rendering app 3
Rendering sub component 0
...
Here's a JSFiddle: http://jsfiddle.net/jor0xu1a/1/
I'm aware that the example SubComponent doesn't need a state but I tried making it as simple as possible to show my problem.
What am I missing?
In SubComponent it is props not state - change it to this.props.count and this will work
I recommend to read Props in getInitialState Is an Anti-Pattern.
Basically, as few components as possible should have state. As the other answers already said, in your case you can just use this.props.count to refer to the current value. There doesn't seem to be any reason why SubComponent should have its own state.
However, if you really want to compute the component's state from the props it receives, it is your responsibility to keep them in sync, with the life cycle method componentWillReceiveProps:
componentWillReceiveProps(nextProps) {
this.setState({count: nextProps.count});
}
You SubComponent should be:
class SubComponent extends React.Component {
constructor(props) {
super(props);
console.log("Creating sub component");
}
render() {
return (<div>count: {this.props.count}</div>);
}
}
My bad, I thought that the constructor (or getInitialState for ES5) is called whenever the component is being re-rendered by the parent (I thought that the parent 're-creates' its children on render) but that's not always the case. I should had read up on it (url) and tried it with ES5 (jsFiddle) before thinking it was something I didn't understand with ES6 and creating a question here.
And yes, the example SubComponent should use this.props but my use case had actual stateful functionality in my real component. I created the example as I thought for some reason that the result weren't the expected outcome when using ES6 (but it was).
Thank you for you feedback!