I've faced with problem using React and React Material-UI components. What I need:
1) User clicks button in my component - I should add mousemove listener to the page and show ProgressBar.
2) User moves mouse - I count events, and update my ProgressBar.
3) When count of events is 50, I remove mousemove listener and hide ProgressBar.
I tried to do this with React useEffect, useState Hooks, but it does not remove listener. I don't understand, why.
Here is my code:
const [completed, setCompleted] = React.useState(0);
const [keyGenState, setKeyGenState] = React.useState(0);
const updateMousePosition = ev => {
console.log("UMP");
setCompleted(old => old + 1);
/*I tried to check completed value here, but it always is 0 - maybe, React re-renders component on setState..
And I decided to take useEffect hook (see below)*/
};
useEffect(() => {
console.log(completed); /*Just to understand, what happens) */
if (completed === 49) {
return () => {
/*When completed value is 50, this log message appears, but mouse listener still works! */
console.log("Finish!");
document.removeEventListener("mousemove", updateMousePosition);
setKeyGenState(2);
}
}
}, [completed]);
function handleChange(e) {
switch (e.currentTarget.id) {
/*startKeyGen - it is ID of my Button. When user clicks it, I show ProgressBar and add mousemove listener*/
case "startKeyGen" : {
setKeyGenState(1);
document.addEventListener("mousemove", updateMousePosition);
break;}
}
}
/*Other logics. And finally, JSX code for my ProgressBar from Material-UI*/
<LinearProgress hidden={keyGenState !== 1 } variant="determinate" value={completed} style={{marginTop: 10}} />
It looks really strange: why React ignores removeEventListener.
Please, explain, where is my mistake.
UPD: Thanks a lot! I used useCallback hook, in this manner:
const updateMousePosition = React.useCallback(
(ev) => {
//console.log("Calback");
console.log(ev.clientX);
setCompleted(old => old + 1);
},
[],
);
useEffect(() => {
//console.log(completed); /*Just to understand, what happens) */
if (completed === 49) {
return () => {
/*When completed value is 50, this log message appears, but mouse listener still works! */
console.log("Finish!");
document.removeEventListener("mousemove", updateMousePosition);
setKeyGenState(2);
}
}
});
But I still don't understand completely.. So, when I used useCallback with empty dependencies array, this function (updateMousePosition), will be unchanged during all "life" of my component? And in useEffect I remove mouseListener. It is magic for me: why does useEffect ignore removing without useCallback?
Try to use React.useCallback for updateMousePosition. Every change in your component creates new function (reference). So React.useEffect remove last updateMousePosition but doesn't remove added in handleChange.
Related
My intention is to update the 'isEditorFocused' state whenever the focused element changed, and if the div contains the focused element, deliver true into the Editor component.
However, the code does not work as my intention... It updates state only the first two times.
This is my Code. Actually not the exact code, but it is the core part of my question. If there is any typo, please ignore it. I checked it all in my real code file.
export default AddArticle = () => {
const [isEditorFocused, setIsEditorFocused] = React.useState(false);
const editorRef = React.useRef(null);
React.useEffect(() => {
if(editorRef.current !== null) {
if(editorRef.current.contains(document.activeElement)
setIsEditorFocused(true);
else
setIsEditorFocused(false);
}
}, [document.activeElement]}
return (
<div ref={editorRef} tabIndex="0">
<Editor isEditorFocused={isEditorFocused}></Editor>
<FileUploader {some props}/>
</div>
)
}
Not to completely change your code, but couldn't you just use onFocus and onBlur handlers?
For example:
const AddArticle = () => {
const [isEditorFocused, setIsEditorFocused] = React.useState(false);
return (
<div
onFocus={() => {
setIsEditorFocused(true);
}}
onBlur={() => {
setIsEditorFocused(false);
}}
tabIndex="0"
>
<Editor isEditorFocused={isEditorFocused}></Editor>
</div>
);
};
Working codepen
As T J mentions so eloquently, your issue is with document.activeElement
Note regarding React's current support for onFocus vs onFocusIn:
React uses onFocus and onBlur instead of onFocusIn and onFocusOut. All React events are normalized to bubble, so onFocusIn and onFocusOut are not needed/supported by React.
Source: React Github
The main problem is this: [document.activeElement].
The useEffect dependency array only works with React state, and document.activeElement is not React state.
You can try using a focusin event listener on your <div>, if it receives the event it means itself or something inside it got focus, since focusin event bubbles as long as nothing inside is explicitly preventing propagation of this event.
try this way.
const AddArticle = () => {
const [isEditorFocused, setIsEditorFocused] = React.useState(false);
const handleBlur = (e) => {
setIsEditorFocused(false)
};
handleFocus = (){
const currentTarget = e.currentTarget;
if (!currentTarget.contains(document.activeElement)) {
setIsEditorFocused(true);
}
}
return (
<div onBlur={handleBlur} onFocus={handleFocus}>
<Editor isEditorFocused={isEditorFocused}></Editor>
</div>
);
};
folks!
Does anyone know the opposite method to cellFocused in ag-grid?
I need to detect when the focused cell loses its focus and run some actions.
Thanks for your responses.
I've found a way to support onBlur event. Since ag-grid doesn't have a built-in method, I created wy own event listener to the focus cell node and remove it after losing the focus state.
So, my code looks like this. Inside the react class I have 3 additional methods:
removeCellBlurListener = () => {
const target = document.activeElement;
if (target) {
target.removeEventListener('blur', this.onCellBlur);
}
};
addCellBlurListener = () => {
const target = document.activeElement;
if (target) {
target.addEventListener('blur', this.onCellBlur);
}
};
onCellBlur = () => {
...do something on blur
};
render () {
return (
<AgGridReact
{...restProps}
onCellFocused={(e) => this.addCellBlurListener()}
onGridReady={this.onGridReady}
/>
);
}
How to delay 300ms and take only last event from mouseLeave event stream Observable in RxJS? I wanted to take latest event only and delay it to 300 milli seconds then fire a method.
class MouseOverComponent extends React.Component {
state = {menuIsOpen: false}
componentDidMount() {
this.mouseLeave$ = Rx.Observable.fromEvent(this.mouseDiv, "mouseleave")
.delay(300)
.throttleTime(300)
.subscribe(() => /* here I want to hide the div */);
}
componentWillUnmount() {
this.mouseLeave$.unsubscribe();
}
menuToggle = e => {
e && e.preventDefault()
let {menuIsOpen} = this.state
menuIsOpen = !menuIsOpen
this.setState({menuIsOpen, forceState: true})
}
render() {
// const menuStateClass = ... resolving className with state
return (
<div ref={(ref) => this.mouseDiv = ref}>
Move the mouse and look at the console...
</div>
);
}
}
but its not working its firing previous events also. Its hiding and showing uncontrollable while i do fast mouse leave.
I want mouseDiv when mouse leaves from the div and wait for 300ms then hide.
Add a first() and repeat() will reset your stream from clean state and it probably can solve your issue.
Rx.Observable.fromEvent(block, "mouseleave")
.delay(300)
.throttleTime(300)
.first()
.repeat()
.subscribe(console.log);
fiddle: http://jsfiddle.net/cy0nbs3x/1384/
I think by "take latest event only" you mean you want to get the last value from fromEvent(this.mouseDiv, "mouseleave") when you call this.mouseLeave$.unsubscribe();.
By calling .unsubscribe() you dispose the chain which is not what you want in this case. Instead you can use takeUntil and takeLast(1) operators like the following to complete the chain that triggers takeLast(1) that passes the last value it received:
componentDidMount() {
this.mouseLeave$ = Rx.Observable.fromEvent(this.mouseDiv, "mouseleave")
.takeUntil(this.unsub$)
.takeLast(1)
.delay(300)
.subscribe(() => /* here I want to hide the div */);
}
componentWillUnmount() {
this.unsub$.next();
}
I have a react component that uses scroll events. When the scroll event is called it basically runs the handler as expected. However I need to be able to call a method once when the scroll events begin to fire. I understand the idea of a debounce method which would fire when the scroll stops, but I need to find a way to fire once when scrolling begins. (For sure NO jQuery can be used).
componentDidMount() {
window.addEventListener('scroll', this.onScroll);
this.setState({
// sets some state which is compared in a shouldComponentUpdate
});
}
componentWillUnmount() {
window.removeEventListener('scroll', this.onScroll);
}
shouldComponentUpdate(nextProps, nextState) {
return shallowCompare(this, nextProps, nextState);
}
The handler seen below runs some code:
onScroll() {
this.scrollTop = document.documentElement.scrollTop;
this.update();
}
But I need a function that runs once:
scrollStart() {
}
I would love to say I have tried something but unfortunately I have no ideas. Any assist would be greatly appreciated.
There is no real scrolling state in the browser; the scroll event happens, and then it's over.
You could e.g. create a new timeout each time the user scrolls and set your own scrolling state to false if the user hasn't scrolled until the timeout function is run.
Example
class App extends React.Component {
timeout = null;
state = { isScrolling: false };
componentDidMount() {
window.addEventListener("scroll", this.onScroll);
}
componentWillUnmount() {
window.removeEventListener("scroll", this.onScroll);
}
onScroll = () => {
clearTimeout(this.timeout);
const { isScrolling } = this.state;
if (!isScrolling) {
this.setState({ isScrolling: true });
}
this.timeout = setTimeout(() => {
this.setState({ isScrolling: false });
}, 200);
};
render() {
return (
<div
style={{
width: 200,
height: 1000,
background: this.state.isScrolling ? "green" : "red"
}}
/>
);
}
}
ReactDOM.render(<App />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="root"></div>
Do you want the scrollStart() function to only fire once, the very first time a user scrolls? If do, this could be easily accomplished with a scrollStarted variable. if (scrollStarted == false) { scrollStarted = true; scrollStart(); }.
I can imagine a similar scenario if you want the function to fire when a user starts scrolling from the top (it can fire again if the user returns to the top). Just replace (scrollStarted == false) with scrollTop == 0.
There is no scrollstart event in javascript, however you can register pointer events on the parent element and scroll events on the target element.
Then, for example, in the pointerdown callback reset a variable that gets set when scrolling starts.
If you want you can even dispatch a custom "scrollstart" event on the target when the scroll event is triggered and var scrolling is not set.
For document.body you can listen for pointer ( or touch or mouse ) events on window.
For this you could define a static variable and when the scroll starts, put true in the variable and enter a while that keeps checking if the scrool continues. Using this logic, you may be able to do something.
I could explain what I am trying to do, but this ReactJS example is a walkthrough of exactly what I want. The problem is I can't figure out what the equivelant would be for react native.
Basically, when I press return in the TextInput, I want the text cleared and focus maintained.
Any thoughts?
I've submitted a PR with a blurOnSubmit property.
Set it to false and the TextInput never blurs, onSubmitEditing still fires though.
Hopefully it gets merged. :)
https://github.com/facebook/react-native/pull/2149
I came out with following (working) solution:
var NameInput = React.createClass({
getInitialState() {
return {
textValue: ''
}
},
clearAndRetainFocus: function(evt, elem) {
this.setState({textValue: elem.text});
setTimeout(function() {
this.setState({textValue: this.getInitialState().textValue});
this.refs.Name.focus();
}.bind(this), 0);
},
render() {
return(
<TextInput
ref='Name'
value={this.state.textValue}
onEndEditing={this.clearAndRetainFocus} />
)
}
});
So, basically when we end editing, we will set the textValue state to the value of the TextInput and right after that (in setTimeout), we switch it back to default (empty) and retain focus on the element.
I don't know how to trigger blurOnSubmit but if you do and it works you should do that. Another thing I found that works with a functional react component in a chat application i am making is this:
... import statments
const ChatInput = props => {
const textIn = React.useRef(null) //declare ref
useEffect(()=>textIn.current.focus()) //use effect to focus after it is updated
const textInputChanged = (text) =>{
props.contentChanged(text);
}
const submitChat = () =>{
const txt = props.content.trim()
txt.length >0 ? props.sendChat(txt, props.username) : null;
}
const keyPressEvent = (e) =>{
return e.key == 'Enter'? submitChat() : null;
}
return (
<TextInput
style={styles.textInput}
keyboardType={props.keyboardType}
autoCapitalize={props.autoCapitalize}
autoCorrect={props.autoCorrect}
secureTextEntry={props.secureTextEntry}
value={props.content}
onChangeText={textInputChanged}
onKeyPress={keyPressEvent}
autoFocus={true} //i don't think you need this since we are using useEffect
ref={textIn} //make it so this is the ref
/>
)}
... export default react-redux connect stuff
if you have more inputs you can probably do some sort of ref choosing logic in the useEffect hook
this is the article that helped me figure it out, it's almost the same thing:
https://howtocreateapps.com/how-to-set-focus-on-an-input-element-in-react-using-hooks/