React パフォーマンス

Loops with Ionic Components

When using loops with Ionic components, we recommend using React's key attribute. This allows React to re-render loop elements in an efficient way by only updating the content inside of the component rather than re-creating the component altogether.

By using key you can provide a stable identity for each loop element so React can track insertions and deletions within the iterator. Below is an example of how to use key:

MyComponent.tsx

import React, { useState } from 'react';
import { IonContent, IonItem, IonLabel, IonPage } from '@ionic/react';

export const MyComponent: React.FC = () => {
  const [items, setItems] = useState([{ id: 0, value: 'Item 0' }, { id: 1, value: 'Item 1' }, ...]);

  return (
    <IonPage>
      <IonContent>
        {items.map(item => {
          return (
            <IonItem key={item.id}>
              <IonLabel>{item.value}</IonLabel>
            </IonItem>
          )
        })}
      </IonContent>
    </IonPage>
  )
}

In this example, we have an array of objects called items. Each object contains a value and an id. Using the key attribute, we pass the item.id for each object. This id is used to provide a stable identity for each loop element.

For more information on how React renders lists using key see: https://react.dev/learn/rendering-lists#keeping-list-items-in-order-with-key