react-usememo

问题 I m having one child component which is inside a loop of parent component. when one of the child components is updating the state of parent component, it is re-rendering the all children since it is loop. How can i avoid the re-render for each iteration. function Parent() { const [selectedChild, setSelectedChild] = useState([]); const onChangeHandle = (event, id) => { const checked = event.target.checked; let updatedArray = [...selectedChild]; if(checked){ if(!selectedChild.includes(id)){

问题 I m having one child component which is inside a loop of parent component. when one of the child components is updating the state of parent component, it is re-rendering the all children since it is loop. How can i avoid the re-render for each iteration. function Parent() { const [selectedChild, setSelectedChild] = useState([]); const onChangeHandle = (event, id) => { const checked = event.target.checked; let updatedArray = [...selectedChild]; if(checked){ if(!selectedChild.includes(id)){

问题 Scenario is relatively simple: we have a long-running, on-demand calculation that occurs on a remote server. We want to memoize the result. Even though we are fetching asychronously from a remote resource, this isn't a side effect because we just want the result of this calculation to display to the user and we definitely don't want to do this on every render. Problem: it seems that React.useMemo does not directly support Typescript's async/await and will return a promise: //returns a promise

问题 I have a MarketOverview component that renders a bunch of cryptocurrency trading pair markets. On initialisation, I want it to render the BTC/USD market by default, which I'm doing via useEffect() . The problem is the defaultMarket gets called on every render. Moreover, defaultMarket depends on the tickers prop, so if I wrap it in useMemo() , then the eslint react-hooks plugin automatically populates tickers as a dependency. Without useMemo() : const defaultMarket = tickers.find((ticker) => {

问题 If we see in the doc example: https://reactnavigation.org/docs/auth-flow/ : function SignInScreen() { const [username, setUsername] = React.useState(''); const [password, setPassword] = React.useState(''); const { signIn } = React.useContext(AuthContext); // ???? return ( <View> <TextInput placeholder="Username" value={username} onChangeText={setUsername} /> <TextInput placeholder="Password" value={password} onChangeText={setPassword} secureTextEntry /> <Button title="Sign in" onPress={() =>

问题 I'm trying to implement a react-table using this guide: https://github.com/tannerlinsley/react-table/blob/master/docs/quickstart.md At one point in the guide, it says to create your data using React.useMemo: const columns = React.useMemo( () => [ { Header: 'Column 1', accessor: 'col1', // accessor is the "key" in the data }, { Header: 'Column 2', accessor: 'col2', }, ], [] ) When I do this, I copy and paste this line into my code (replacing the data with my own data): class Blog extends