Pass the current state of parent component to children through props - javascript

I have a very event-driven component. In this case, it is a video tag which will update its state with the current state of the playing video. For the sake of simplicity, imagine it looks something like this:
export default class VideoPlayer extends Component {
state = {
canPlay: false,
duration: 0,
position: 0,
};
onCanPlay = () => this.setState({ canPlay: true });
onTimeUpdate = ({ target: { position, duration } }) => this.setState({ position, duration });
render() {
const { src, children } = this.props;
return (
<div className={styles.container}>
<video
src={src}
onCanPlay={this.onCanPlay}
onTimeUpdate={this.onTimeUpdate}
/>
{children}
</div>
);
}
}
In this case, I want to pass the entire state of the component to the child. One way I can do it, which feels somewhat convuluted, is to pass a function as children which injects the state and returns a component. For example:
{children(this.state)}
Where the passed in component would be like:
{(state) => <Progress {...state} />}
But I feel like there must be a way to pass the state of the parent component implicitly as props. How would this be done with React?

Maybe you can try with:
<div>
{ React.Children.map(this.props.children,
child => React.cloneElement(child, {...this.state})
)}
</div>

Related

How would I delay a slow React child from re-rendering so the parent can repaint the dom immediately?

Suppose you had a React App component with a child component that was slow to mount (in my case a 3rd party document editor). The App has to re-render whenever the document changes, and the two child components (the header (which simply displays title, id), the document editor (slow to initially render when initializing a document)) should be able to re-render and repaint the dom as soon as they finish updating. However, the document editor, because it is a slow to initialize, prevents the header from repainting until it is complete. Below is an illustration, where the FastChild will not be repainted until the SlowChild returns.
export default function App() {
const [count, setCount] = useState(0);
return (
<div className="App">
<FastChild count={count} />
<button onClick={() => setCount(count+1)}>increment</button>
<SlowChild count={count}/>
</div>
);
}
function FastChild({ count }) {
return (
<h1>{count}</h1>
)
}
function SlowChild({ count }) {
return veryLongList.map(()=> (
<div>
{`count ${count}`}
</div>
))
}
Unfortunately, I cannot make changes the document editor (which would be the SlowChild component in this example).
One solution is to keep a copy of the prop in state, and use shouldComponentUpdate to delay the slow component from rendering using setImmediate
class DelayedSlowChild extends React.Component {
constructor(props) {
super(props)
this.state = {
localCount: props.count,
}
}
shouldComponentUpdate = (nextProps, nextState) => {
if (nextProps.count !== this.props.count) {
setImmediate(() => this.setState({ localCount: nextProps.count }))
return false;
} else if (this.state.localCount !== nextState.localCount) {
return true;
}
return false
}
render() {
veryLongList.map(i => (
<div>
{`${i} ${this.props.count}`}
</div>
))
}
}

React child component state is lost after parent component re-renders

I am using a React hook for parent/child component.
Now I have state in my parent component (companyIcon), which I need to update based on some validation in the child component. I pass validationCallback as a callback function to the child component and update my parent state based on the value I get from the child.
Now the issue is after I update the parent state, the state value in my child component gets reset. What I am doing wrong in the below implementation ?
function ParentComp(props) {
const [companyIcon, setCompanyIcon] = useState({ name: "icon", value: '' });
const validationCallback = useCallback((tabId, hasError) => {
if (hasError) {
setCompanyIcon(prevItem => ({ ...prevItem, value: 'error'}));
// AFTER ABOVE LINE IS EXECUTED, my Child component state "myAddress" is lost i.e. it seems to reset back to empty value.
}
}, []);
const MyChildCmp = (props) => {
const [myAddress, setmyAddress] = useState('');
useEffect(() => {
if (myAddressExceptions.length > 0) {
props.validationCallback('MyInfo', true);
} else {
props.validationCallback('MyInfo', false);
}
}, [myAddressExceptions])
const handlemyAddressChange = (event) => {
//setmyAddress(event.target.value);
//setmyAddressExceptions(event.target.value);
console.log(myAddressExceptions);
}
return (
<>
<div className="row" style={{ display: 'flex', flexDirection: 'row', width: '1000px'}}>
<div style={{ width: '20%'}}>
<FormField
label='Company Address'
required
helperText={mergedErrorMessages(myAddressExceptions)}
validationState={
myAddressExceptions[0] ? myAddressExceptions[0].type : ''
}
>
<Input id='myAddress'
value={myAddress}
//onChange={handlemyAddressChange}
onChange={({ target: { value } }) => {
validateInputValue(value);
}}
onBlur={handleBlur}
inputProps={{maxLength: 9}} />
</FormField>
</div>
</div>
</>
);
}
return (
<div className="mainBlock">
Parent : {companyIcon}
{displayMyChild && <MyChildCmp validationCallback={validationCallback}/>}
</div>
)
}
export default withRouter(ParentComp);
Here are some reasons why you can lose state in child (there could be more, but these apply to you most):
{displayMyChild && <MyChildCmp validationCallback={validationCallback}/>}
Here if at one point displayMyChild is truthy, then made falsy, this means the component MyChildCmp will get unmounted, hence all its state will be gone.
But now, even if you didn't have that condition and rendered the MyChildCmp always you would still run into similar problem, this is because you defined MyChildCmp inside another component. When you do that, on each render of the parent component, the function MyChildCmp is recreated, and the reconciliation algorithm of react thinks you rendered a different component type on next render, so it will destroy the component instance. Move definition of that component outside the parent component.

ComponentDidUpdate doesn't work

I'm trying to render dynamically a collection of component using componentDidUpdate.
This is my scenario:
var index = 0;
class myComponent extends Component {
constructor(props) {
super(props);
this.state = {
componentList: [<ComponentToRender key={index} id={index} />]
};
this.addPeriodHandler = this.addPeriodHandler.bind(this);
}
componentDidUpdate = () => {
var container = document.getElementById("container");
this.state.componentList.length !== 0
? ReactDOM.render(this.state.componentList, container)
: ReactDOM.unmountComponentAtNode(container);
};
addHandler = () => {
var array = this.state.componentList;
index++;
array.push(<ComponentToRender key={index} id={index} />);
this.setState = {
componentList: array
};
};
render() {
return (
<div id="Wrapper">
<button id="addPeriod" onClick={this.addHandler}>
Add Component
</button>
<div id="container" />
</div>
);
}
}
The problem is that componentDidUpdate work only one time, but it should work every time that component's state change.
Thank you in advance.
This is not how to use react. With ReactDOM.render() you are creating an entirely new component tree. Usually you only do that once to initially render your app. Everything else will be rendered by the render() functions of your components. If you do it with ReactDOM.render() you are basically throwing away everything react has already rendered every time you update your data and recreate it from scratch when in reality you may only need to add a single node somewhere.
Also what you actually store in the component state should be plain data and not components. Then use this data to render your components in the render() function.
Example for a valid use case:
class MyComponent extends Component{
state = {
periods: []
};
handleAddPeriod = () => {
this.setState(oldState => ({
periods: [
...oldState.periods,
{/*new period data here*/}
],
});
};
render() {
return (
<div id="Wrapper">
<button id="addPeriod" onClick={this.handleAddPeriod}>
Add Component
</button>
<div id="container">
{periods.map((period, index) => (
<ComponentToRender id={index} key={index}>
{/* render period data here */}
</ComponentToRender>
))}
</div>
</div>
);
}
}
}
Also you should not work with global variables like you did with index. If you have data that changes during using your application this is an indicator that is should be component state.
try
addHandler = () =>{
var array = this.state.componentList.slice();
index++;
array.push(<ComponentToRender key={index} id={index}/>);
this.setState=({
componentList: array
});
}
if that works, this is an issue with the state holding an Array reference that isn't changing. When you're calling setState even though you've added to the Array, it still sees the same reference because push doesn't create a new Array. You might be able to get by using the same array if you also implement shouldComponentUpdate and check the array length of the new state in there to see if it's changed.

Why a child component's state keeps clearing?

I have multiple layers of React components for getting an embed from a music service API, including a higher-order component that hits the API to populate the embed. My problem is that my lowest-level child component won't change state. I basically want the populated embed (lowest level component) to display an album cover, which disappears after clicking it (revealing an iframe), and whose state remains stable barring any change in props higher up (by the time this component is revealed, there should be no other state changes aside from focus higher up). Here's the code:
Parent:
return (
/*...*/
<Embed
embed={this.props.attributes.embed}
cb={updateEmbed}
/>
/*...*/
First child ( above):
render() {
const {embed, className, cb} = this.props;
const {error, errorType} = this.state;
const WithAPIEmbed = withAPI( Embed );
/*...*/
return <WithAPIEmbed
embed={embed[0]}
className={className}
cb={cb}
/>;
/*...*/
withAPI:
/*...*/
componentWillMount() {
this.setState( {fetching: true} );
}
componentDidMount() {
const {embed} = this.props;
if ( ! embed.loaded ) {
this.fetchData();
} else {
this.setState( {
fetching: false,
error: false,
} );
}
}
fetchData() {
/*... some API stuff, which calls the callback in the top level parent (cb()) setting the embed prop when the promise resolves -- this works just fine ...*/
}
render() {
const {embed, className} = this.props;
const {fetching, error, errorType} = this.state;
if ( fetching ) {
/* Return some spinner/placeholder stuff */
}
if ( error ) {
/* Return some error stuff */
}
return (
<WrappedComponent
{...this.props}
embed={embed}
/>
)
}
And finally the last child I'm interested in:
constructor() {
super( ...arguments );
this.state = {
showCover: true,
};
}
render() {
const {embed, setFocus, className} = this.props;
const {showCover} = this.state;
if ( showCover ) {
return [
<div key="cover-image" className={classnames( className )}>
<figure className='cover-art'>
<img src={embed.coverArt} alt={__( 'Embed cover image' )}/>
<i onClick={() => {
this.setState( {showCover: false,} );
}}>{icon}</i> // <-- Play icon referenced below.
</figure>
</div>,
]
}
return [
<div key="embed" className={className}>
<EmbedSandbox
html={iframeHtml}
type={embed.embedType}
onFocus={() => setFocus()}
/>
</div>,
];
}
My issue is that clicking the play icon should clear the album cover and reveal the iframe embed, but even though the click is registering, the state never changes (or does and then changes back). I believe it's because a higher-level component is mounting/unmounting and reinstantiating this component with its default state. I could move this state up the tree or use something like Flux, but I really feel I shouldn't need to do that, and that there's something fundamental I'm missing here.
The problem is that const WithAPIEmbed = withAPI( Embed ); is inside the render method. This creates a fresh WithAPIEmbed object on each render, which will be remounted, clearing any state below. Lifting it out of the class definition makes it stable and fixes the problem.

Focusing div elements with React

Is it possible to focus div (or any other elements) using the focus() method?
I've set a tabIndex to a div element:
<div ref="dropdown" tabIndex="1"></div>
And I can see it gets focused when I click on it, however, I'm trying to dynamically focus the element like this:
setActive(state) {
ReactDOM.findDOMNode(this.refs.dropdown).focus();
}
Or like this:
this.refs.dropdown.focus();
But the component doesn't get focus when the event is triggered. How can I do this? Is there any other (not input) element I can use for this?
EDIT:
Well, It seems this it actually possible to do: https://jsfiddle.net/69z2wepo/54201/
But it is not working for me, this is my full code:
class ColorPicker extends React.Component {
constructor(props) {
super(props);
this.state = {
active: false,
value: ""
};
}
selectItem(color) {
this.setState({ value: color, active: false });
}
setActive(state) {
this.setState({ active: state });
this.refs.dropdown.focus();
}
render() {
const { colors, styles, inputName } = this.props;
const pickerClasses = classNames('colorpicker-dropdown', { 'active': this.state.active });
const colorFields = colors.map((color, index) => {
const colorClasses = classNames('colorpicker-item', [`colorpicker-item-${color}`]);
return (
<div onClick={() => { this.selectItem(color) }} key={index} className="colorpicker-item-container">
<div className={colorClasses}></div>
</div>
);
});
return (
<div className="colorpicker">
<input type="text" className={styles} name={inputName} ref="component" value={this.state.value} onFocus={() => { this.setActive(true) }} />
<div onBlur={() => this.setActive(false) } onFocus={() => console.log('focus')} tabIndex="1" ref="dropdown" className={pickerClasses}>
{colorFields}
</div>
</div>
);
}
}
React redraws the component every time you set the state, meaning that the component loses focus. In this kind of instances it is convenient to use the componentDidUpdate or componentDidMount methods if you want to focus the element based on a prop, or state element.
Keep in mind that as per React Lifecycle documentation, componentDidMount will only happen after rendering the component for the first time on the screen, and in this call componentDidUpdate will not occur, then for each new setState, forceUpdate call or the component receiving new props the componentDidUpdate call will occur.
componentDidMount() {
this.focusDiv();
},
componentDidUpdate() {
if(this.state.active)
this.focusDiv();
},
focusDiv() {
ReactDOM.findDOMNode(this.refs.theDiv).focus();
}
Here is a JS fiddle you can play around with.
This is the problem:
this.setState({ active: state });
this.refs.component.focus();
Set state is rerendering your component and the call is asynchronous, so you are focusing, it's just immediately rerendering after it focuses and you lose focus. Try using the setState callback
this.setState({ active: state }, () => {
this.refs.component.focus();
});
A little late to answer but the reason why your event handler is not working is probably because you are not binding your functions and so 'this' used inside the function would be undefined when you pass it as eg: "this.selectItem(color)"
In the constructor do:
this.selectItem = this.selectItem.bind(this)
this.setActive = this.setActive.bind(this)
This worked in my case
render: function(){
if(this.props.edit){
setTimeout(()=>{ this.divElement.focus() },0)
}
return <div ref={ divElement => this.divElement = divElement}
contentEditable={props.edit}/>
}

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