I have the following code:
const PlayArea = () => {
const [foo, setFoo] = useState('foo')
const [bar, setBar] = useState('bar')
return <div>{bar}</div>
}
In my project, whenever I use setFoo, the whole component re-renders, and I'm trying to prevent that. I only want the component to re-rerender when bar changes.
Is there anyway that I can keep the component from changing from using setFoo ?
Is there anyway that I can keep the component from changing from using
setFoo ?
No. By design state variables work such that when you change them that component will rerender.
But If you don't want to rerender your component when you update that variable then why are you using a state variable? Use useRef
Keep in mind that useRef doesn’t notify you when its content changes.
Mutating the .current property doesn’t cause a re-render.
Related
My application contains a view that is a functional react component. I'm trying to add a timestamp at the bottom of the view displaying the date and time when the user navigated to this view. I'm wondering what would be appropriate way to implement this using hooks. I guess one option would be to use const [date] = useState(new Date()) and simply provide no setter for the state since it would never change. However, this makes me wonder if useState is the appropriate hook to begin with. Should I just do const date = new Date() in the component body or would that have some unexpected side effects?
For what you intend to accomplish, the code below would work just fine:
// solution # 1
function MyComponent() {
const [time, setTime] = useState(new Date());
return (
<div>
View created at {time.toLocaleTimeString()}
</div>
)
}
However, it is important to know that it is not following React rules. That is because we are calling new Date() from inside the component, making it impure. React expects the components to be pure functions. This means that it should return the same thing for the same input. But React cannot guarantee that a function component doesn't have side effects, and that is why that first solution would work just fine.
According to this gist, a better approach for this task would be:
// solution # 2
function MyComponent() {
const [time, setTime] = useState<Date>();
useEffect(() => {
setTime(new Date());
}}, [])
return (
<div>
View created at {time && time.toLocaleTimeString()}
</div>
)
}
Roughly speaking, all side effects should live inside useEffect. So, things like calling an external API or calling impure functions (such as Math.random() or Date.now()) should be there. From my understanding, this solution would be more appropriate.
If we are not obeying React guidelines, the library might not work as advertised. Before version 18, React had only synchronous rendering. This means that the moment the render phase is kicked off (either by a initial render or by a state update), nothing could interrupt it from committing those updates to the browser. In that situation, I don't think the first solution I presented would be problematic. But, in React 18, we have the concurrent mode features by which rendering can be interrupted before the diffs are committed to the screen. With that, React can be more intelligent about how it breaks up all the work it needs to do (for example, we can now define high-priority updates).
In order for these new APIs to work properly, React assumes that the components are pure functions, which means that it has no side effects. These APIs are very new and there are still many more additional features coming in. I am not quite sure about how sensitive they are to function impurity, but I believe our second solution (with all side effects living inside the useEffect) is a better bet for this task.
The following seems to work. Still not sure if this is optimal though.
import React from 'react'
export function View(_props) {
const [viewCreated] = React.useState(Date.now())
return (
<div>
View created {String(new Date(viewCreated))}
</div>
)
}
useState(new Date()) is better. Here is complete component
import React, { useState , useEffect } from 'react'
export const DateTime = () => {
var [date,setDate] = useState(new Date());
useEffect(() => {
var timer = setInterval(()=>setDate(new Date()), 1000 )
return function cleanup() {
clearInterval(timer)
}
});
return(
<div>
<p> Time : {date.toLocaleTimeString()}</p>
<p> Date : {date.toLocaleDateString()}</p>
</div>
)
}
export default DateTime
So I've a custom widget which renders a custom component.
conversion.for('editingDowncast').elementToElement({
model: 'modelName',
view: (modelElement, viewWriter) => {
const modelName = modelElement.getAttribute('modelName');
const modelNameView = viewWriter.createContainerElement('span', {
class: 'modelName',
'data-modelName': modelName,
});
const reactWrapper = viewWriter.createUIElement(
'span',
{
class: 'modelName__react-wrapper',
},
function (this, domDocument) {
const domElement = this.toDomElement(domDocument);
rendermodelName(modelName, domElement);
return domElement;
},
);
viewWriter.insert(
viewWriter.createPositionAt(modelNameView, 0),
reactWrapper,
);
return toWidgetEditable(modelNameView, viewWriter);
},
});
Where rendermodelName will give back a React component with a simple input box as
return (
<div>
<input type="text" />
</div>
);
https://ckeditor.com/docs/ckeditor5/latest/builds/guides/integration/frameworks/react.html.
But the problem is, whenever I tried to add some content inside the input, the focus is lost from the field and automatically moved to the surrounding editor. What am I missing. Tried creating a focushandler and adding the modelNameView to it.
Should I go with the new createRawElement? My current CK5 is 20.0.0 So I don't want any breaking changes coming now.
EDIT:
I researched a little bit more. seems like createRawElement may not work here. I think this doesn't have a simple solution. I tried with allowContentOf: '$block' which also not letting me focus. But these values are explicitly for normal CK widget, not for a react component.
I had the same issue and solved it by adding this tag to the parent div that wraps my Vue component.
https://ckeditor.com/docs/ckeditor5/latest/framework/guides/deep-dive/ui/widget-internals.html#exclude-dom-events-from-default-handlers
Adding from CKE Docs:
Sometimes it can be useful to prevent processing of events by default handlers, for example using React component inside an UIElement in the widget where, by default, widget itself wants to control everything. To make it possible the only thing to do is to add a data-cke-ignore-events attribute to an element or to its ancestor and then all events triggered by any of children from that element will be ignored in default handlers.
Let’s see it in an short example:
<div data-cke-ignore-events="true">
<button>Click!</button>
</div>
In the above template events dispatched from the button, which is placed inside containing data-cke-ignore-events attribute, will be ignored by default event handlers.
I faced the similar issue.
CKEditor will takes all the events on React component which you hosted on Widget.
The work around is to stop propagation of events to CKEditor which are fired from your DOM element(domElement) where your React component hosted.
Here is the sample code:
https://github.com/ckeditor/ckeditor5-core/compare/proto/input-widget#diff-44ca1561ce575490eac0d660407d5144R239
You should stop all required events. Also you can't paste any content inside the input field of React component. That will also listened by clipboardInput event of CKEditor.
I'm having issue getting the React Fabric UI DetailsList to work with React Hooks. It renders, but the selection part does not. Whenever, you select a row, I expect the count of the selection to be updated. However, i'm not seeing that. It looks like the selection component items never get updated even thou the UI shows it being selected. I'm also seeing the onSelectionChange being triggered when you select a row. Now sure if its because i'm using react hooks or what
I took the provided class example which works:
[Codepen]https://codepen.io/pen/?&editable=true (Example)
Same as the original but stripped down
[Codepen]https://codepen.io/darewreckk/pen/NQRWEd?editors=1111
converted it to a react hook component. I would expect the same thing, but i'm not and can't figure out what's different.
Modified Example with Hooks
[Codepen]https://codepen.io/darewreckk/pen/GVjRNb?editors=1111
Any advice appreciated,
Thanks,
Derek
The selection count is stored on the Selection object that you are creating. You could log it out like so:
const _selection = new Selection({
onSelectionChanged: () => {
console.log('Selected count:' + _selection.count);
}
});
You can set the value of selectionCount and selectionDetails whenever onSelectionChanged is called:
const _selection = new Selection({
onSelectionChanged: () => {
setSelectionCount(_selection.count);
setSelectionDetails(`${_selection.count} items selected`)
}
});
As a side note: If you want selectionDetails to update when selectionCount updates, you can use the useEffect hook:
React.useEffect(() => {
setSelectionDetails(`${selectionCount} items selected`);
}, [selectionCount]);
The above effect will run whenever selectionCount updates, and so in turn update selectionDetails.
in a react UI I have a table component. You can edit one row of the table by clicking a edit button or you can add a new record by clicking a "new-record-button". When clicking the edit button an redux-action is triggered which takes the row and sets a visible property of a modal dialog. When the "new-record-button" is clicked an action is triggered which creates a new empty data item and the same modal dialog is triggered.
In the modal dialog I have several text components with onChange method.
in this onChange-method the data-item is written.
When to user clicks a save-button the edited dataItem is saved to the database.
So my code looks like:
const mapStateToProps = (state) => ({
dataItem: state.datItemToEdit || {},
...
});
...
handleTextChange(event) {
const {
dataItem
} = this.props;
const id = event.target.id;
const text = event.target.value;
switch (id) {
case 'carId': {
dataItem.carId = text;
break;
}
...
}
this.forceUpdate();
}
...
<TextField
...
onChange={event => this.handleTextChange(event)}
/>
I have several question regarding this approach. First I do not understand why in handleTextChange we can write to dataItem. It does work apparently.
dataItem.carId is set in the example code but I thought
const {dataItem} = this.props;
gives us a local read-only variable dataItem just to read from the props...
Next thing I think is a poor design. After reading in a book about react I think we should not write to props but only set a state.
In my example I get the the dataItem from the redux-state. The mapStateToProps maps it to the (read-only) props of the component, right?!. But I want to EDIT it. So I would have to copy it to the state of my component?
But where to do it?
Once in the state of my component I could simply call this.setState for the various text-fields and the component would render and I could abstain from forceUpdate(), right?!
Can someone explain how the redux status plays together with the component status and props for this example?
In redux or react, you shouldn't write to the props directly because you should keep your props as immutable. Redux forces us to use immutable state because state is a source of truth for the application. If the reference to state changes then only your app should render. If you'll mutate your state (objects) then the references don't get changed and your app doesn't know whether some state has been changed or not. React/Redux doesn't give you read-only objects automatically. You can mutate them anytime but as I told you, it can cause problems that Your app won't know when to re-render. If you want to have this read-only property inherently, you should probably use immutable.js
About your second question that you'll have to copy the props to the component's state and where you should do it. You should do it in the constructor of the component and you should use immutibility helper
import React from React;
import update from 'immutibility-helper';
class Modal extends React.Component {
constructor(props){
this.state = {
dataItem: dataItem,
};
}
...other methods
handleTextChange(event) {
const {
dataItem
} = this.props;
const id = event.target.id;
const text = event.target.value;
switch (id) {
case 'carId': {
this.props.updateItem(this.state.dataItem, text); //fire a redux action to update state in redux
this.setState(update(this.state, {
dataItem: {
carId: {$set: text},
}
});
break;
}
...
}
}
}
You wouldn't have to do forceUpdate in such case because the reference to state will change and the component will re-render itself.
Also, you can use forceUpdate in your application but personally I don't find it a great idea because when React/Redux is giving you the flow of state, by using forceUpdate, you're breaking the flow.
The last question is how redux and react state plays together. That is also a matter of choice. If I have a app level state, e.g., in your case you've some app level data, you should put that in your redux state and if you have a component level things, such as opening a modal or opening a third pane. That's the convention I follow but that can really depend on how you want to exploit react and redux state.
Also, in above code, I put the redux state in component state too (because you asked where to put that) but Ideally you should fire a redux action and update in redux state. In this way, you will restrict yourself from state duplication in react and redux.
import React from React;
import {updateItem} from './actions';
class Modal extends React.Component {
...other methods
handleTextChange(event) {
const {
dataItem
} = this.props;
const id = event.target.id;
const text = event.target.value;
switch (id) {
case 'carId': {
this.props.updateItem(this.props.dataItem, text); //fire a redux action to update state in redux
break;
}
...
}
}
}
const mapStateToProps = (state) => ({
dataItem: getDataItem(state), //get Data Item gets Data from redux state
});
export default connect(mapStateToProps, {updateItem: updateItem})(Modal);
in Actions:
updateItem = (dataItem, text) => dispatch => {
dispatch({type: 'UPDATE_ITEM', payLoad: {dataItem, text});
};
in Reducer:
export default (state = {}, action) => {
switch(action){
case 'UPDATE_ITEM': {
return {
...state,
dataItem: {
...action.dataItem,
carId: action.text,
}
};
}
}
}
In this way, your state will be pure and you don't have to worry about immutibility.
EDIT:
As constructor will be called only once, you should probably use componentWillReceiveProps so that whenever you render the component, you get the next updated props of the component. You can check whether the carId of dataItem is same or not and then update the state.
componentWillReceiveProps(nextProps){
if(nextProps.dataItem.carId !== this.props.dataItem.carId){
this.setState({dataItem: nextProps.dataItem});
}
}
You should only use redux when you want different, unrelated components in your app to know and share the specific state.
e.g. - When a user logs in to your app, you might want all components to know that user so you'll connect your different containers to the user reducer and then propagate the user to the components.
Sounds like in this case you have a classic use case for using the inner state.
You can use the parent of all TextFields to maintain all rows, edit them by index, etc.
Once you start using redux, it's really easy to make the mistake of transferring the entire state of the components to the reducers, I've been there and stopped doing it a while ago :)
Imagine the following React structure:
SmartComponentA -> DumbComponentB -> SmartComponentC
Also imagine that SmartComponentA and SmartComponentC each get connected to different slices of the state in their mapStateToProps functions.
Lastly, imagine that we put a console.log in the render method of each of these components.
When I actually try this, on the first render, I see that all components log as expected. But then if I change the data for SmartComponentC, I only see a single log message (C's log message), and I don't see SmartComponentA or DumbComponentB logging anything. How is that possible? How is react-redux getting React to update a child without updating its parents?
I would have assumed that the overriding of shouldComponentUpdate inside of the connect method would mean SmartComponentA would not get re-rendered (since its slice of the state didn't change), and therefore would cause a short-circuiting that would prevent SmartComponentC from getting re-rendered. While connect's implementation is not the same as the pure render mixin, both work by changing shouldComponentUpdate, but the pure render docs clearly state that React will "bail out" (as they put it) if a parent doesn't need to re-render:
for C2's subtree and C7, it didn't even have to compute the virtual DOM as we bailed out on shouldComponentUpdate.
source
If my question still isn't clear, here is sort of pseudo-code for the setup, and I'm asking why I can keep typing in C's input and it only log's C's messages to the console and not A's and B's (why is it not short-circuiting)?
//////////////////////////////////////////////
const SmartComponentA = (props) => {
console.log('rendering SmartComponentA');
return <DumbComponentB bData={props.bData} />;
};
const mapStateToProps = (state) => { bData: state.bData };
export default connect(mapStateToProps)(SmartComponentA);
//////////////////////////////////////////////
const DumbComponentB = (props) => {
console.log('rendering DumbComponentB');
return (
<div>
{props.bData}
<SmartComponentC />
</div>
);
}
export default DumbComponentB;
//////////////////////////////////////////////
const SmartComponentC = (props) => {
console.log('rendering SmartComponentC');
return (
<div>
<input value={props.cValue} onChange={props.changeCValue} />
</div>
);
}
const mapStateToProps = (state) => { cValue: state.cValue };
export default connect(mapStateToProps, { changeCValue })(SmartComponentC);
//////////////////////////////////////////////
On the first render I see all log messages, then if I keep typing in the input, I only see C's log message each time I press a key.
Prop changes trigger the React component lifecycle which will typically trigger the lifecycle of each child component unless -- as you observe, the process can be short-circuited by shouldComponentUpdate.
But prop changes aren't they only thing that triggers the component lifecycle -- state changes do too. And that's how connect function works. The Connect component subscribes to the store and on any store change checks to see if it will update the smart component's props (based on mapStateToProps). If so it will set it's own state triggering the lifecycle functions for the Connect component and it's child.