Data Messages

A Data Message is a Message whose content is raw bytes instead of a dictionary. Like a Message, it's delivered immediately and only works while the Watch is reachable. Check isWatchReachable before sending.

On the JavaScript side the bytes are always a base64 encoded string. That applies to what you send, the Replies you get back, the data you receive and the Replies you send. The Watch app gets the decoded bytes as Data.

• Outbound (iPhone → Watch): sendDataMessage asks for a Reply, and sendDataMessageWithoutReply doesn't.
• Inbound (Watch → iPhone): onDataMessageReceived fires for a Data Message that doesn't ask for a Reply, and onDataMessageWithReply fires for one that does.

A string that isn't valid base64 fails with ERR_INVALID_BASE64 before anything is sent, and its message says what's wrong with it. For text, btoa and atob encode and decode base64.

sendDataMessageCopy Anchor Link

sendDataMessage(data: string): Promise<string>

Sends a Data Message to the Watch and waits for its Reply.

The Watch app must receive it with a reply handler and call it, in session(_:didReceiveMessageData:replyHandler:). If it never replies, the Promise rejects with ERR_MESSAGE_REPLY_TIMED_OUT.

Parameters

Returns Promise<string>, which resolves with the Watch's Reply, base64 encoded.

Throws (the Promise rejects with):

WatchConnectivity can fail with other codes too. See Error codes for the full list.

Example

import RnWatchConnect, { type WatchConnectErrorCode } from "rn-watch-connect";

try {
  const reply = await RnWatchConnect.sendDataMessage(btoa("Hello from iPhone!"));
  console.log("Reply:", atob(reply));
} catch (error) {
  const code = (error as { code?: WatchConnectErrorCode }).code;
  if (code === "ERR_WATCH_NOT_REACHABLE") {
    // Try again when onReachabilityChanged says the Watch is reachable.
  }
}

sendDataMessageWithoutReplyCopy Anchor Link

sendDataMessageWithoutReply(data: string): Promise<void>

Sends a Data Message to the Watch without asking for a Reply. The Watch app receives it in session(_:didReceiveMessageData:).

Parameters

Returns Promise<void>, which resolves once the Data Message is handed to the Session.

Throws (the Promise rejects with):

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

Example

import RnWatchConnect from "rn-watch-connect";

if (RnWatchConnect.isWatchReachable) {
  await RnWatchConnect.sendDataMessageWithoutReply(btoa("tap"));
}

onDataMessageReceivedCopy Anchor Link

onDataMessageReceived: (event: { data: string }) => void

Fires when an Inbound Data Message arrives that doesn't ask for a Reply.

Event

Example

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

export function DataListener() {
  useEventListener(RnWatchConnect, "onDataMessageReceived", ({ data }) => {
    console.log("From the Watch:", atob(data));
  });
  return null;
}

Outside a component, use RnWatchConnect.addListener("onDataMessageReceived", listener), and call remove() on the subscription when you're done.

onDataMessageWithReplyCopy Anchor Link

onDataMessageWithReply: (event: DataMessageWithReplyEvent) => void

Fires when an Inbound Data Message arrives that asks for a Reply. Answer it by calling the event's Reply function, reply.

Event

Each Data Message takes one Reply:

• If several listeners get the same Data Message, the first reply call wins. Later calls reject.
• A Data Message can stop waiting for its Reply, for example when its last listener is removed. Calling reply after that rejects.

reply throws (its Promise rejects with):

Example

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

export function EchoResponder() {
  useEventListener(RnWatchConnect, "onDataMessageWithReply", ({ data, reply }) => {
    reply(btoa(`Got: ${atob(data)}`));
  });
  return null;
}

replyToDataMessageCopy Anchor Link

replyToDataMessage(replyId: string, response: string): Promise<void>

Sends the Reply to an Inbound Data Message, using the replyId from its onDataMessageWithReply event.

Parameters

Returns Promise<void>, which resolves once the Reply is sent.

Throws (the Promise rejects with):

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

Moving to reply

// Before (deprecated)
useEventListener(RnWatchConnect, "onDataMessageWithReply", ({ data, replyId }) => {
  RnWatchConnect.replyToDataMessage(replyId, btoa("ok"));
});

// After
useEventListener(RnWatchConnect, "onDataMessageWithReply", ({ data, reply }) => {
  reply(btoa("ok"));
});