<!--
{
  "availability" : [
    "iOS: 15.0.0 -",
    "iPadOS: 15.0.0 -",
    "macCatalyst: 15.0.0 -",
    "macOS: 12.0.0 -",
    "tvOS: 15.0.0 -",
    "visionOS: 1.0.0 -"
  ],
  "documentType" : "symbol",
  "framework" : "GroupActivities",
  "identifier" : "/documentation/GroupActivities/CustomMessageIdentifiable/messageIdentifier",
  "metadataVersion" : "0.1.0",
  "role" : "Type Property",
  "symbol" : {
    "kind" : "Type Property",
    "modules" : [
      "Group Activities"
    ],
    "preciseIdentifier" : "s:15GroupActivities25CustomMessageIdentifiableP17messageIdentifierSSvpZ"
  },
  "title" : "messageIdentifier"
}
-->

# messageIdentifier

A custom identification string for the current type.

```
static var messageIdentifier: String { get }
```

## Discussion

The string you return from this property must be unique among your app’s
custom message types. When you send a message, [`GroupSessionMessenger`](/documentation/GroupActivities/GroupSessionMessenger) includes
this string in the data it sends to other devices. When it receives a message,
[`GroupSessionMessenger`](/documentation/GroupActivities/GroupSessionMessenger) creates the type that contains the matching string in
this property.

---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)