use-state

问题 Setup/Scenario I am using twitter api to fetch data and rendering it in twitter card using react-native-socials. The tweet data ( JSON ) is stored and served through my backend and rendered in the app. I am using a Flatlist to render this data. Problem It's working fine for the first 3 loads, I am using pullToRefresh in flatlist to do a network call to get new data. But when I try the 4th time it gets an undefined element. I've replaced the Twitter element ( from react-native-socials lib )

问题 Setup/Scenario I am using twitter api to fetch data and rendering it in twitter card using react-native-socials. The tweet data ( JSON ) is stored and served through my backend and rendered in the app. I am using a Flatlist to render this data. Problem It's working fine for the first 3 loads, I am using pullToRefresh in flatlist to do a network call to get new data. But when I try the 4th time it gets an undefined element. I've replaced the Twitter element ( from react-native-socials lib )

问题 Setup/Scenario I am using twitter api to fetch data and rendering it in twitter card using react-native-socials. The tweet data ( JSON ) is stored and served through my backend and rendered in the app. I am using a Flatlist to render this data. Problem It's working fine for the first 3 loads, I am using pullToRefresh in flatlist to do a network call to get new data. But when I try the 4th time it gets an undefined element. I've replaced the Twitter element ( from react-native-socials lib )

问题 I am trying to fetch data from json file in firebase. I get this error before the app loads sometimes. The App still works. Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function. Kindly help me to fix this. Here is my code : const [dataSource, setData] = useState([]); useEffect(() => { fetch("https://jsonurlcomeshere

问题 const startLive = () => { // connect to websocket only on start button setliveChartState({ ...liveChartState, liveActive: !liveChartState.liveActive, historicLiveActive: true, start: new Date(), }); /*- - - -after updation - - - >*/ const { ws, liveActive } = liveChartState; // if clicked on stop then close websocket if (!liveActive && ws) { ws.close(); clearLiveInterval(); } // if clicked on start and websocket close then connect if ((!ws || ws.readyState === WebSocket.CLOSED)&& liveActive)

问题 I tried to set a state using useState inside useEffect with no problem, code as follows: import React, {useState, useEffect} from 'react'; const Banner = () => { const [title, setTitle] = useState([]); useEffect(() => { async function fetchData() { const api = 'some api url'; let response = await fetch(api); response = await response.json(); setTitle(response.title); } fetchData(); }) } export default Banner; Now I'd like to do the same thing but with useReducer, I tried to modify the above

问题 I have a Provider that provides a state variable and its corresponding setter through two contexts . const BookedBatchContext = createContext({}) const SetBookedBatchContext = createContext(null) const initialState = { id: null } The Provider looks like this: export const BookedBatchProvider = ({ children }: { children: any }) => { const [bookedBatch, setBookedBatch] = useState(localState ||initialState) return ( <SetBookedBatchContext.Provider value={setBookedBatch}> <BookedBatchContext

问题 How can I change a specific value of an array using useState without modifying it's position. For example: if I wouldn't use useState , I can modify the array like this: checkBox[2] = true . I tried setCheckBox[2](true) but it does work. Can anyone help me with this issue. const [checkBox, setCheckBox] = useState( [true, false, false, false, false, false, false, false] ); how can I change the value in index 2 of this array to true without changing the position? 回答1: setCheckBox[2](true) -

问题 I'm going to introduce my question in two steps with slightly different code blocks in both. Step 1: Below we have a React application which renders itself every two seconds and therefore causes the browser to print render to the console. If the user presses any key, the renders will stop which in turn stops the console prints. Please ignore the line commented out for now. import { useState, useEffect, useRef } from 'react'; function App() { const [number, setUpdate] = useState(0); const

问题 import React, { useState} from "react"; import ReactDOM from "react-dom"; function App() { const [count, setCount] = useState(0); function handleAlertClick(){ return (setTimeout(() => { alert("You clicked on: " + count); }, 3000)) } return ( <div> <p>You clicked {count} times</p> <button onClick={() => setCount(count + 1)}>Click me</button> <button onClick={handleAlertClick}>Show alert</button> </div> ); } I just want to know if this works the way that I think it does, or if there is a better