setstate

How to update state in react synchronously

由 。_饼干妹妹 提交于 2019-12-08 09:18:35
问题 onSave=()=>{ if (this.state.intialValue<=0) { this.setState({errorIntialValue: true}) } else { this.setState({errorIntialValue: false}) } if (this.state.age>=25|| this.state.age<=-1) { this.setState({errorAge: true}) } else{ this.setState({errorAge: false}) } if (this.state.rollNo<0) { this.setState({errorRollno: true}) } else{ this.setState({errorRollno: false}) } if(!(this.state.errorIntialValue|| this.state.errorAge ||errorRollno)){ //have to enter only if no error let newData={

React: set State or set Prop without a Rerender

由 那年仲夏 提交于 2019-12-08 06:41:30
Problem: Currently, I have a LoginForm component that has an "on-success" handler function handleOnSuccess . This the then linked to the parent component with an onTokenUpdate property defined by a "token-update" handler function handleUpdateToken . The problem is that the setState in the handleUpdateToken function is forcing an undesired rerender. Desired Outcome: What I ultimately need is to update the LoginForm component property token with the value obtained on success WITHOUT performing a rerender. Is this even possible? According to React: Update Child Component Without Rerendering

How to set state of the value when using react-rating component in my form?

由 好久不见. 提交于 2019-12-08 05:41:56
问题 I'm using React Rating (https://github.com/dreyescat/react-rating) and I'm not sure how to set state for the values for my 2 ratings. The other fields are fine. I'm able to get the values to show in console. I don't know how to set state in handleRatingChange(). Also, when I fill out the other fields after I have done the ratings, the ratings resets. Here is my code: var Rating = require('react-rating') class Assignment extends Component { constructor(props) { super(props) this.state = { form

How should one use the setState() method in ReactJS?

由 陌路散爱 提交于 2019-12-07 15:15:32
问题 I'm new to ReactJS and I'm trying to understand state and setState() . Using setState() I wanted to change a name, but I am not sure where I should call the setState() method in my code: Inside the constructor OR Inside the render method OR Create a custom method and call it at the end of the constructor before render() is called This is my code: import React from "react"; class StateBasic extends React.Component{ constructor(){ super(); let personProfile = this.state = { name : "Bob", skill

How to use setState() in React to blank/clear the value of an array

由 北城以北 提交于 2019-12-07 04:02:36
问题 I am trying to clear an array, but I'm having trouble. this.setState({warnErrorTypes:[]}) I'm not sure if I am dealing with a race condition, or what the specific issue is, but I can see that the value of my array is consistently wrong in the case that I need to reset its value to []. How does one replace an array that contains [1,2] with [] then subsequently [3] where the following are true: this.state.warnErrorTypes is an Array which starts out with [] Based on condition, 2 is pushed in

Flutter: Does it matter what code is in setState()?

由 删除回忆录丶 提交于 2019-12-06 19:31:49
问题 When we want a StatefulWidget to rebuild we call setState() but does it really matter if the code we type is inside that function or outside of it? Is this: class _ShoppingListState extends State<ShoppingList> { Set<Product> _shoppingCart = new Set<Product>(); void _handleCartChanged(Product product, bool inCart) { setState(() { if (inCart) _shoppingCart.add(product); else _shoppingCart.remove(product); }); } } the same as this: class _ShoppingListState extends State<ShoppingList> { Set

I have one this.state and i need pass in my componentDidMount with setState, how use bind(this) in setState?

由 ε祈祈猫儿з 提交于 2019-12-06 10:01:30
I have that pass Bind in setState, how to do? enter image description here TypeError: Cannot read property 'setState' of undefined I am using the RealTime Firebase and ReactJs constructor() { super() this.app = firebase.initializeApp(firebase_config); this.database = this.app.database().ref().child('users'); this.state = { users: [] } } componentDidMount() { this.database.once("value", function(snapshot) { snapshot.forEach(function(data) { this.setState({users: data.val()}) }) }); } render() { return ( <BrowserRouter> <div className="App"> <Navbar/> <Switch> <Route exact="exact" path='/'

How can I pass event to setState callback function?

由 允我心安 提交于 2019-12-06 02:30:17
问题 Is it possible in React to pass an external event to the callback function of setState? Example someFunc(event) { this.setState( { value: event.target.value }, () => { this.props.onChange(event); // <- cannot pass to here } ); } EDIT: See accepted solution below by Liam for an excellent answer, Here is the specific solution to my problem: Solution someFunc(event) { event.persist() // <- add this line and event should pass without a problem this.setState( { value: event.target.value }, () => {

How should one use the setState() method in ReactJS?

由 ⅰ亾dé卋堺 提交于 2019-12-05 22:03:00
I'm new to ReactJS and I'm trying to understand state and setState() . Using setState() I wanted to change a name, but I am not sure where I should call the setState() method in my code: Inside the constructor OR Inside the render method OR Create a custom method and call it at the end of the constructor before render() is called This is my code: import React from "react"; class StateBasic extends React.Component{ constructor(){ super(); let personProfile = this.state = { name : "Bob", skill : "Art Designer", location : "LA" } console.log(personProfile); } render(){ let changeName = this

Real world usage of setState with an updater callback instead of passing an object in React JS

由 扶醉桌前 提交于 2019-12-05 20:48:40
The React documentation says the following about setState : If you need to set the state based on the previous state, read about the updater argument below , Beside the following sentence, which I don't understand: If mutable objects are being used and conditional rendering logic cannot be implemented in shouldComponentUpdate() , calling setState() only when the new state differs from the previous state will avoid unnecessary re-renders. They say: The first argument is an updater function with the signature (state, props) => stateChange ... state is a reference to the component state at the
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