Linking and Deep Links

Linking works in both directions. Outward, Linking.openURL(url) hands a URL to the system, which opens a browser for https:, the dialer for tel:, the mail app for mailto: and maps for geo:; openSettings() opens your app's settings page, and on Android sendIntent(action, extras) fires any intent. Inward, a deep link opens your app at a particular screen. It needs a URL scheme, which Expo 6,418 declares from "scheme": "booknest" in app.json, and your code reads the URL with Linking.getInitialURL() on a cold start and the url event while the app runs.

src/interact/LinkingDemo.tsx: incoming URLs and canOpenURL() (excerpt)TSX

const targets = ['https://example.com', 'mailto:orders@example.com', 'tel:+15550100',
  'geo:0,0?q=bookshop', 'booknest://book/2', 'spotify:album:1'];
// ...inside LinkingDemo:
  useEffect(() => {
    Linking.getInitialURL().then((url) => console.log('initial URL:', url));   // cold start
    const sub = Linking.addEventListener('url', ({ url }) => console.log('url event:', url));
    (async () => {
      for (const url of targets) console.log(url.padEnd(28), await Linking.canOpenURL(url));
    })();
    return () => sub.remove();
  }, []);

The app was opened from the launcher, and then sent a link with adb shell am start -a android.intent.action.VIEW -d booknest://book/2 com.anonymous.booknest:

Output of 111

 LOG  initial URL: null
 LOG  https://example.com          true
 LOG  mailto:orders@example.com    false
 LOG  tel:+15550100                false
 LOG  geo:0,0?q=bookshop           false
 LOG  booknest://book/2            true
 LOG  spotify:album:1              false
 LOG  url event: booknest://book/2

mailto: and tel: came back false although Gmail 1 and the dialer are installed, yet the Email the shop button's openURL('mailto:...') opened Gmail. Since Android 11, an app sees other apps only through the <queries> in its manifest, and the Expo template declares only https. Declare the schemes you ask about, or skip canOpenURL() and catch the rejection from openURL().

MENU