Application Context

The Application Context is a dictionary describing the latest values the other side needs, such as a selected theme or the current score. It's delivered in the background, so the Watch doesn't have to be reachable. Only the most recent one is delivered: each update replaces the previous one.

Because an update replaces the whole dictionary, send everything the Watch needs each time, not just what changed. If every value matters, not only the latest, queue User Info instead.

Each side has its own Application Context:

• Outbound (iPhone → Watch): updateApplicationContext sends one. applicationContext is the last one you sent.
• Inbound (Watch → iPhone): onApplicationContextChanged fires when one arrives. receivedApplicationContext is the last one received.

A dictionary's values must be ones WatchConnectivity can carry: strings, numbers, booleans, arrays and nested objects.

updateApplicationContextCopy Anchor Link

updateApplicationContext<T extends Record<string, any>>(applicationContext: T): Promise<void>

Sends a new Application Context to the Watch, replacing the previous one. The Watch app receives it in session(_:didReceiveApplicationContext:).

Type parameters

Parameters

Returns Promise<void>, which resolves once the Session has taken the update. Delivery happens later, in the background.

Throws (the Promise rejects with):

WatchConnectivity can fail with other codes too, such as ERR_SESSION_NOT_ACTIVATED, ERR_DEVICE_NOT_PAIRED or ERR_WATCH_APP_NOT_INSTALLED. See Error codes for the full list.

Its error message starts with Expo's prefix, "Calling the 'updateApplicationContext' function has failed", so match on code.

Example

import RnWatchConnect from "rn-watch-connect";

type WatchDisplay = { theme: "light" | "dark"; units: "metric" | "imperial" };

await RnWatchConnect.updateApplicationContext<WatchDisplay>({
  theme: "dark",
  units: "metric",
});

applicationContextCopy Anchor Link

readonly applicationContext: Record<string, any>

The last Application Context this iPhone sent with updateApplicationContext. It's {} when there's none, and on platforms other than iOS.

Example

import RnWatchConnect from "rn-watch-connect";

// Change one value and send the rest unchanged.
await RnWatchConnect.updateApplicationContext({
  ...RnWatchConnect.applicationContext,
  theme: "light",
});

receivedApplicationContextCopy Anchor Link

readonly receivedApplicationContext: Record<string, any>

The last Application Context received from the Watch. It's {} when there's none, and on platforms other than iOS. Read it for the starting value, then listen to onApplicationContextChanged for new ones.

onApplicationContextChangedCopy Anchor Link

onApplicationContextChanged: (applicationContext: Record<string, any>) => void

Fires when a new Application Context arrives from the Watch. The listener gets the whole dictionary, which replaces the previous one.

It fires only when one actually arrives, not when you add a listener. For the starting value, read receivedApplicationContext.

Example

import { useEvent } from "expo";
import RnWatchConnect from "rn-watch-connect";

export function WatchTheme() {
  const context = useEvent(
    RnWatchConnect,
    "onApplicationContextChanged",
    RnWatchConnect.receivedApplicationContext,
  );
  return `Theme on the Watch: ${context.theme ?? "default"}`;
}