How do you save and read local files with FileSystem and share content through the Sharing API?

Short answer

Use expo-file-system to download files to DocumentDirectory or CacheDirectory, then use expo-sharing to share them with other apps.

Explanation

DocumentDirectory is for permanent user-owned files that remain available in backups, while CacheDirectory is for temporary files that the system may delete when storage is low. Sharing.shareAsync opens the native system share sheet to send reports and PDFs through email or WhatsApp.

Code example

import * as FileSystem from 'expo-file-system';
import * as Sharing from 'expo-sharing';

async function downloadAndSharePDF(url: string) {
  const fileUri = FileSystem.documentDirectory + 'invoice.pdf';
  const downloadResult = await FileSystem.downloadAsync(url, fileUri);

  if (await Sharing.isAvailableAsync()) {
    await Sharing.shareAsync(downloadResult.uri);
  }
}

Common mistakes

• Saving large temporary cache files in DocumentDirectory, increasing the app's iCloud and Google Drive backup size.

Follow-up questions

• How do you manage local and remote push notifications and their tokens?

Sources

• Expo docs — FileSystem
• Expo docs — Sharing