hooks+memo

function Parent() {
    const [count, setCount] = useState(1);
    const [val, setValue] = useState(‘‘);

    const getNum = useCallback(() => {
        return Array.from({length: count * 100}, (v, i) => i).reduce((a, b) => a+b)
    }, [count])

    return <View>
        <Child getNum={getNum} />
        <View>
            <TouchableOpacity onPress={() => setCount(count + 1)}><Text>+1</Text></TouchableOpacity>
            <TextInput value={val} onChangeText={event => setValue(event)}/>
        </View>
    </View>;
}

const Child = React.memo(function ({ getNum }: any) {
    console.log(getNum)
    return <Text>总和：{getNum()}</Text>
})