useIsFocused

• focused 될 때 호출됨.

• focused 상태인지 true/false 반환.

• (focused state가 바뀌므로) focused 될 때마다 스크린을 re-render 시킴.

• 무겁다면 React.memo 또는 React.PureComponent로 re-render를 최소화 시켜야 함.

import * as React from 'react';
import { Text } from 'react-native';
import { useIsFocused } from '@react-navigation/native';

function Profile() {
  // This hook returns `true` if the screen is focused, `false` otherwise
  const isFocused = useIsFocused();

  return <Text>{isFocused ? 'focused' : 'unfocused'}</Text>;
}