setstate

问题 I want to disable the setState message warning On the layout 1 : My constructor : constructor(props){ super(props); //Constructeur this.lestachesitemsRef=getDatabase().ref('n0rhl66bifuq3rejl6118k8ppo/lestaches'); this.lestachesitems=[]; this.state={ //Debutdustate lestachesSource: new ListView.DataSource({rowHasChanged: (row1, row2)=>row1 !== row2}), Prenom: '', Nom: '',} } My function : ajouter= () => { if( (this.state.Nom !== '') && (this.state.Prenom !== '')) { this.lestachesitemsRef.push(

问题 I am trying to implement to Show More/Show Less. So far I have was able to bring up a ItemViewer Component where in I display the list of items. For each section there would be Show More / Show Less links. Show More should be visible whenever the number of items is greater than 3 and it should be able to toggle(Show More/ Show Less). When the number of items is less than 3 dont show the link. Also when there is no data display "No data found". I have come up with a sandbox : https:/

问题 I know I should not mutate state directly in React, but how about situation when I use function: onSocialClick = e => { const id = e.target.value; this.setState((prevState, props) => { prevState[id] = !(prevState[id]); return prevState; }); }; Is it a mistake to modify passed object? EDIT: It turns out that most of us were wrong here. React docs state it clearly now: state is a reference to the component state at the time the change is being applied. It should not be directly mutated. Instead

问题 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()

问题 This question already has answers here : How to use a variable for a key in a JavaScript object literal? (13 answers) Reactjs setState() with a dynamic key name? (9 answers) react setState with dynamic key (1 answer) Closed last year . From an input field I am sending the value as an argument to the function that sets state. I have multiple input fields so would like to use their name (which is equal to their state key) to then use the same function and pass in the key and value to the

问题 Problem I am writing an application in React and was unable to avoid a super common pitfall, which is calling setState(...) after componentWillUnmount(...) . I looked very carefully at my code and tried to put some guarding clauses in place, but the problem persisted and I am still observing the warning. Therefore, I've got two questions: How do I figure out from the stack trace , which particular component and event handler or lifecycle hook is responsible for the rule violation? Well, how

问题 What's the major difference bewteen these two functions? handleOnChange(evt) { this.setState(() => ({ tickerName: evt.target.value })); } handleOnChange(evt) { this.setState({ tickerName: evt.target.value }); } And why with the handleOnChange() function that change the state directly this works fine? <input type="text" value={this.state.tickerName} onChange={(evt) => this.handleOnChange(evt)} /> When I use the first function that change the state with a callback I get this error: TypeError:

问题 When a react component state changes, the render method is called. Hence for any state change, an action can be performed in the render methods body. Is there a particular use case for the setState callback then? 回答1: Yes there is, since setState works in an asynchronous way. That means after calling setState the this.state variable is not immediately changed. so if you want to perform an action immediately after setting state on a state variable and then return a result, a callback will be

问题 When a react component state changes, the render method is called. Hence for any state change, an action can be performed in the render methods body. Is there a particular use case for the setState callback then? 回答1: Yes there is, since setState works in an asynchronous way. That means after calling setState the this.state variable is not immediately changed. so if you want to perform an action immediately after setting state on a state variable and then return a result, a callback will be

问题 i'm brand new to Flutter. I'm trying to open a panel pressing a button and than closing it by pressing a button on that panel. I've managed to do it by writing the code in the same page. What i can't do is splitting the code and keep everything working. What I'm actually doing is calling a variable in the State of a widget that is initialized False and then with an if statement i'm calling: or an empty container or the panel i want. When i press the button i call SetState(){} and the variable